The ecological research on coral reefs of the Red Sea

The ecological research on coral reefs of the Red Sea

855 THE E C O L O G I C A L R E S E A R C H ON CORAL REEFS OF THE RED SEA Hans Mergner H u h F - U n i v e r s i t a t Bochum, Lchrstuhl fur Speziel...

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855

THE E C O L O G I C A L R E S E A R C H ON CORAL REEFS OF THE RED SEA

Hans Mergner H u h F - U n i v e r s i t a t Bochum, Lchrstuhl fur Spezielle Zoologic, D-4630 Bochum, Federal Republic of Germany

ABSTRACT K l u n z i n g e F (1872) c h a r a c t e r i s e d the z o n a t i o n of the coral reef near AI-Qusayr, Egypt w i t h the help of indicator species. He i d e n t i f i e d a S t y l o p h o r a - z o n e among other zones and e s t a b lished the first b i o p h y s i o g r a p h i c z o n a t l o n of a coral reef which is, in many respects, still v a l i d today. Since then, e c o l o g i c a l r e s e a r c h w o r k on coral reefs has d e v e l o p e d to its present u n d e r s t a n d i n g of one of the most c o m p l i c a t e d and densely populated e c o s y s t e m s on Earth. Much biological and ecological w o r k has been done on the coral reefs along the Red Sea coasts. This is not surprising, b e c a u s e the Red Sea is the coral sea closest to Europe and has attracted the interest of E u r o p e a n i n v e s t i g a t o r s for over 200 years. With few e x c e p t i o n s , this interest has been c o n c e n t r a t e d on a l i m i t e d number of coastal sites: Jeddah, A I - Q u n f u d h a h , A i - L u h a y y a h and A i - M u k h a along the east coast, and Assab, Mesewa, A i - Q u s a y r and A s - S u w a y s along the west coast. A l t h o u g h the early coral reef workers were primarily i n t e r e s t e d in c o l l e c t i n g animals, they also m a d e some informal observations on the h a b i t a t s of the species they collected. However, full e c o l o g i c a l statements were rare - with the e x c e p t i o n of those of K l u n z i n g e r (1872). R e s e a r c h centres have been e s t a b l i s h e d and active programmes continue on the S u d a n e s e coast at D u n g u n a b (since 1907), S a w a k i n and Bur Sudan (since 1963 when the first e c o l o g i c a l investigations on Bur Sudan coral r e e f s o c c u r r e d (Mergner, 1967),and in 1974 and 1976 r e s p e c t i v e l y the b i o l o g i c a l stations at S a w a k i n and Bur Sudan were established), on the E g y p t i a n coast at A I - G h a r d a q a (since 1930 ),on the Sinai coast at Eilat (since 1968) and on the J o r d a n coast at A i - A q a b a h (since 1972). New r e s e a r c h centres continue to open, such as along the east coast at Jeddah. The special interest of the e c o l o g y of Red Sea coral reefs is that it e n c o m p a s s e s a b r o a d r a n g e of problems: the influence of a b i o t i c factors on the community structure, d i s t r i b u t i o n and species d i v e r s i t y of corals and the b i o p h y s i o g r a p h i c zonation of coral reefs, the inters p e c i f i c and i n t e r g e n e r i c c o m p e t i t i o n of corals and other sessile animals and algae w i t h i n the reef, the q u a l i t a t i v e and q u a n t i t a t i v e analysis of the coral a s s e m b l a g e s of d i f f e r e n t r e e f zones and the e c o l o g y of several important reef animal groups (sponges, m o l l u s c s , e c h i n o derms, fishes, etc.). C l o s e l y c o n n e c t e d w i t h these problems is an interest in the behavio%u" of reef animals, and f i n a l l y r e e f e c o l o g i s t s cannot ignore the urgency of the p r o b l e m s 8 s s o c iated with the p o l l u t i o n and c o n s e r v a t i o n of coral reefs in the Red Sea.

H, Mergner

856

.i

Lagoon fringing reef 6km south of A q a b a harbour. Underwater view of fore reef and reef slope. U n d e r w a t e r drawing by Hans M e r g n e r (Mergner & Schuhmacher, 1974).

INTRODUCTION:

THE RED SEA AS A C O R A L SEA

This review deals with b i o l o g i c a l problems of the shallow shelf seas w h i c h are seldom m o r e than 200m deep. It will only discuss the biology and e c o l o g y of the benthos (including littoral fishes) and will not include pelagic life. It will discuss only coral reefs and will not deal with m a n g r o v e areas. Firstly, I will discuss why such impressive coral r e e f s have developed in the Red Sea. I will then review the h i s t o r y of the biological e x p l o r a t i o n of the Sea and the initial attempts at ecological r e s e a r c h a l o n g its coastline. Finally, I will report in more detail on the present situation, present p r o b l e m s and future a~ms of coral reef ecology w i t h i n this Sea.

Among all the h i o t o p e s inhabited by amlmals, the coral reefs have the h i g h e s t p o p u l a t i o n density. Their b i o c o e n o s e s are composed of most classes of animals, and c h a r a c t e r l a e d by an e x t r a o r d i n a r y number and d l v e r s ~ t y of species.. Indeed, representatives of almost all animal phyla and classes can be found a s s o c i a t e d with reefs. Only the A r a c h n l d a , apart from watermites, and the insects, apart from the gerrid H a l o b a t e s (which lives on the surface of the water), are not represented. In this review, e m p h a s i s is given to the importance of coral reefs as e c o s y s t e m s and particularly to the necessity of conducting detailed ecological studies of them. Coral reefs extend almost continuously along nearly all coasts in tropical seas, so reef ecology is generally s y n o n y m o u s with ecology of tropical coastlines and their s h a l l o w waters. But what makes the Red Sea such an exemplary coral sea? To answer this q u e s t i o n some geog r a p h i c a l remarks are necessary. First, both the t o p o g r a p h i c a l and climatic conditions of the Red Sea are quite exceptional. It lies in a long and deep rift-valley, which has only narrow and shallow connections to the oceans at either end by the Suez Canal and Straits of Bab-el-Mandeb, arid these allow only a limited e x c h a n g e of surface water. Furthermore,

Coral

Heels

of the Red Sea

857

this s e m i - i s o l a t e d basin is s i t u a t e d in a desert-belt which is e x t r e m e l y hot and dry, so there is a trivial a m o u n t of p r e c i p i t a t i o n and almost no inflow of freshwater. Its h y d r o graphic conditions are unique, because both the surface water t e m p e r a t u r e s arc u n u s u a l l y high and the deeper w a t e r is isothermal (21.7"C) down into abyssal depths, and the high e v a p o r a t i o n Fate r e s u l t s in very high surface salinities which can exceed 40 10 -3. Furthermore, the b r e a d t h of the c o n t i n e n t a l shelf flanking both sides of the central trench has f a v o u r e d the d e v e l o p m e n t of e x t e n s i v e COral reefs. At present wide areas diversified environment (Klauscwitz,

the e x t e n s i v e s h a l l o w water zones of the shelf provide s u i t a b l e habitats over for the d e v e l o p m e n t of coral reefs and c o n s e q u e n t l y the reef faunas are g r e a t l y with a large n u m b e r of endemic species: such d i v e r s i t y can only arise in an with a long c o n t i n u i t y of pa]aeogeographic h i s t o r y llke that of the Red Sea 1964).

A c c o r d i n g to Krenkel (1925), the Red Sea was formed during the early T e r t i a r y by the o p e n i n g of the rift which is part of the big A r a b i a n - E a s t African r i f t - v a l l e y system. It is possible, however, that the n o r t h e r n part of the so-called "Erythrean Trench" down to A I - Q u s a y r was formed first and f i l l e d from an arm of the Mediterranean, while in the m i d d l e and s o u t h e r n parts there were still f r e s h w a t e r lakes. At the beginning of the upper Miocene, the whole rift d e e p e n e d along its axis and w i d e n e d forming a u n i f o r m inland sea which was s e p a r a t e d from the I n d o - P a c l f i c by the A b y s s i n i a n land-barrier near the present Straits of B a b - e l - M a n d e b , but it had several c o n n e c t i o n s to the north with the Tcthys. The s o u t h e r n t h r e s h o l d sank d u r i n g the upper P l i o c e n e c o n n e c t i n g the ErythraeanTrench w i t h the I n d o - P a c i f i c for the first time. The n o r t h e r n c o n n e c t i o n s w i t h the Tethys were s e v e r e d by e p i r o g e n e t i c drifts during the diluvium, and r e m a i n e d c l o s e d until man linked the M e d i t e r r a n e a n by the c o n s t r u c t i o n of the Suez Canal. D u r i n g the P l e i s t o c e n e there w e r e several eustatic f l u c t u a t i o n s in sea level c a u s e d by the glaciations. During the ice ages the lowering of sea level probably led to t e m p o r a r y isolation, and hence h y p e r s a l i n a t i o n of the Red Sea, because the Straits of B a b - e l - M a n d e b c o n n e c ting the I n d o - P a c i f i c d r i e d up. K l a u s e w i t z (1964) e m p h a s i s e d the c o n s e q u e n c e s of this isolation on the c o m p o s i t i o n of the fish fauna and the e v o l u t i o n of a high degree of endcmism. According to his h y p o t h e s i s , the fish fauna was originally M e d i t e r r a n e a n w h i c h was later m i x e d w i t h and e v e n t u a l l y r e p l a c e d by an Indo-Pacific fish fauna. This newest c o m p o n e n t is s u p p o s e d not to h a v e i m m i g r a t e d before the last p o s t g l a c l a l period. It can be a s s u m e d that a s i m i l a r series of events o c c u r r e d in other marine animal groups. Since the d i l u v i a l period, the r i f t - v a l l e y of the Red Sea, apart from minor m o v e m e n t s , has been stable.

HISTORY

OF T H E B I O L O G I C A L

EXPLORATION

OF THE RED SEA

The g e o g r a p h i c a l peculiarities of the Red Sea, its p a l a e o g e o g r a p h i c a l o r i g i n and its close p r o x i m i t y to Europe has a t t r a c t e d the interest of European i n v e s t i g a t o r s for o v e r 200 years. Because this interest continues to persist, the history of the z o o l o g i c a l e x p l o r a t i o n of this sea is s u m m a r i s e d here. (See Figs. 1 and 2). The first s c i e n t i s t to visit the Red Sea was the Swedish z o o l o g i s t Forssk~l, who from 1761 until 1763 t r a v e l l e d aa part of a D a n i s h m i s s i o n mainly along the east coast near Jcddah, AI-Luhayyah and Ai-Mukha. He d i e d in 1763 at the age of 31 at Y a r i m / Y e m e n from m a l a r i a , but his c o l l e c t i o n of m a t e r i a l s w a s b r o u g h t back to C o p e n h a g e n by the only s u r v i v i n g m e m b e r Niebuhr, who in 1775 p u b l i s h e d m a n y of Forssk~l's d e s c r i p t i o n s i n c l u d i n g the d e s c r i p t i o n of 146 species of fish. D u r i n g the French c a m p a i g n to Egypt led by Napoleon b e t w e e n 1798 "and 1801, Mediterranean and Red Sea fish w e r e collected, and the d e s c r i p t i o n s of this p u b l i s h e d by G e o f f r o y S a l n t - H i l a i r e (1829).

a number of m a t e r i a l were

E h r e n b e r g and H e m p r i c h f r o m B e r l i n w e r e the next zoologists to visit the Red Sea. From 1820 to 1826 they w o r k e d m a i n l y a r o u n d l e d d a h and A I - Q u n f u d h a h on the east coast and M e s e w a on the west coast where B e m p r i c h d i e d in 1825. Ehrenberg r e t u r n e d to Berlin w i t h a rich b i o l o g ical c o l l e c t i o n w h i c h c o n t a i n e d m a n y corals which he d e s c r i b e d in 1834(a): "Beitr~ge zur p h y s i o l o g i s c h e n Kenntni8 der C o r a l l e n t h i e r e im allgemeinen, und b e s o n d e r s des rothen Meeres, nebst e i n e m V e r s u c h zur p h y s i o l o g i s c h e n S y s t e m a t i k dcrselben". His fish collection, w h i c h c o n t a i n e d m o r e than 500 species, i n c l u d i n g 59 new ones, was the subject of a series of twentytwo p u b l i c a t i o n s by Cuvier and V a l e n c i e n n e s (1828-1849).

H. N e r g n e r

858

Fig.l. Red Sea area of the first 1 Forssk~l 2 Ehrenberg

known at the time of C.B. Klunzinger with the locations zoologlcal investigatlons (after Klausewitz, 196~): (1761-63) 6 Kossmann (1874-75) & Hemprlch (1820-26) 7 Boutourllne, Traversl (1881-87)

3 4

R~ppel (1822-31) g l u n z i n g e r (1862-75)

5

Issel,

At about the same time,

Becari

8 9

Bottego (1891) Stetndachner (1895-97)

(1879)

Ruppell t r a v e l l e d through North A f r i c a and in 1826 s t a r t e d c o l l e c t i n g

flehes near At-Tur/Penlnsula of Sinai, at Jeddah and Nesewa. He described 161 flsh species, 75 of them new in 1828. Followlng a second voyage made between 1831 and 1833, when Ruppell vlslted As-Suway8, Jeddah and Mesewa, he published a further list of 351 species from the Red Sea (Ruppel, 1835). The next famous zoological investigator was a German doctor, Klunzinger, who a f t e r learning A r a b i c w o r k e d f r o m 1864 a t A I - Q u s a y r as a medical officer. He s t u d i e d the local coral reefs collecting corals, fishes and v a r i o u s invertebrates such as molluscs and echinoderms until 1869. He p u b l i s h e d h~s most important w o r k on h i s return to Germany "Synopsis der Pische

Coral

l~eefs of the Hed Sea

859

des Rothen Meeres" (Klunzlnger, 1870-71) w h i c h remains u n s u r p a s s e d as the s t a n d a r d w o r k on Red Sea fishes. K l u n z i n g e r r e t u r n e d to A I - Q u s a y r in 1872 for a further three years. During this period he made the first study of b i o p h y s i o g r a p h l c z o n a t l o n of coral reefs, the results of which are still valid in many r e s p e c t s (Klunzinger, 1872). Later he p u b l i s h e d (1877, 1879a,b, 1906, 1913) a series of m o n o g r a p h s on groups of reef animals, the most important of which were the three volumes e n t i t l e d " K o r a l l t h i e r e des Rothen Meeres". These early zoological i n v e s t i g a t o r s were primarily interested in fish c o l l e c t i o n s and their description. Less e m p h a s i s was placed on the coral reefs, their formation a n d faunal stocks, the exceptions were the first d e s c r i p t i o n of coral reefs by Ehrenberg (18]~b) in "Uber die Natur und B i l d u n g der C o r a l l e n b M n k e des vothen Meeres", and the first e c o l o g i c a l statement and discussion of b i o p h y s i o g r a p h i c z o n a t i o n by K l u n z i n g e r (1872) in " Z o o l o g i s c h e Excursion auf ein K o r a l l e n r i f f des Rothen Meeres bei Koss6r". 40*

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20 Formica - E~pedition ( I ) 21 Warifa . E~(pedlfion { A ~ G) 22 Is/ael-Soufh Red S e a - £ x F fls~) 23 M e t e o r . Expedition ( G) 2, 3, ¢, 6, 24 ABEL (Au.) S. I o . . 25 5EHEER ( G ) Mesewa 26 KLAUSEWITZ ( G ) 15. 27 IMAGNU~ ( G ) 28 E I B L - E I B E S F E L D T (A~, G) 2g 51LLNER ( O ] 3o /4ERGNER ( G ) Am. - American 31 f i l S H E L S O N , P O R ((sr.) AU. -- A~tr;~n 3Z ORhfOND, CAMPBELL ( B ) B = Br/f, sh E = Egyptian 33 fiRICKE (G) F . I:¢en~h 34 L OYA and Co-Workers ( lsr.) G = ~man 35 VINE ( B ) I~ Israelian 36 SCHUHMA(HER { G ) l - lfali,~n 37 JHASTALLER ( G ) 5 - Suedish 38 $VOBODA (G)

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Map o f

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Red

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reefs.

H. M e r g n e r

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After the opening of the Suez Canal in 1869, research interest increased. Kossman (1875, 1866), collected fishes (15 new species) and invertebrates in the Mesewa area and the Dahlak Archipelago. Both fish and invertebrates were also collected by Italian captains from along the Erythrean coast n e a r Mesewa and Asab e.g. the collections of Issel and Becari in 1870 (see Issell and Canefri 1876-1877), Boutourline and Traversi i n 1884-1887, of Bottego in 1891 (see Del Prato, 1891), and finally by Ors~ni (see Pellegrin, 1912). Steindachner (1898) led two expeditions to the Red Sea in 1895/96 and 189~ and between 1890 and 1900 the first extensive hydrographic investigations were made by the Italian vessel 'SCILLA' in the southern Red Sea; 154 fish species were collected in the area of Mesewa and the Dahlak Archipelago. From 1904, Crossland worked on the fauna of the Sudanese coast. He administered the S u d a n Pearl Fishery until 1922, and in 1910 he established the Marine Biological Station at A1-Ghardaqa where be remained as director until 1938. His first fish collection from As-Suways and Sawakin including 91 species was revised by Bamber (19]5), his second from AI-Ghardaqa by Dunker (1940). Biological research throughout the Red Sea area has been carried out from blgger expeditions. Of those before World War II, the hydrographic expedition of the 'AMIRAGLIO MAGNAGHI' 1923/24 (Sanzo 1926, 1930), the 'AL-SAYAD' Expedition to the Gulfs of As-Suways and AI-Aqabah 1928/29 (Dollfus 1938, 1967) and, of course, the "John Murray Expedition" on the Egyptian Research Vessel 'MABAHISS' in 1933/34. After the World War II, larger expeditions have included: the 'MANIHINE' Expedition 1950/51 (Marshall 1952), to the Gulf of AI-Aqabah with the Sinai coast and Titan and to Bur Sudan, the 'CALYPSO' Expedition 1951/52 (Cousteau, Nesteroff and Tazieff 1952, 1953) to the Farasan Archipelago and the Isle of Abulat, and the 'FORMICA' Expedition 1952/53 (Baschieri-Salvadorl 1954, 1955) to the Dahlak Archipelago followed by the 'XARIFA' Expedition 1957/58 (H. Hess) to Jubal, AI-Ghardaqa, Mukawwar, Shab Ambar and the Farasan Archlpelago with ecological studies at the Isle of Sarso. In addition Co the "International Indian Ocean Expedition'" were the "Israel South Red Sea Expedition" in 1962 (Steinitz 1965) to the Dahlak Archipelago (Isle of Entedebir) which included oceanographic and marine biological studies and assembled a collection of 280 fish species, and 1964/65 the 'METEOR' Expedition (Dietrich, K~ause, Seibold and Vollbrecht, 1966) which traversed the whole Red Sea but paid special attention to the southern part and the ecology of the Isle of Sarso in the Farasan Archipelago. There has been a steady increase in number of individual investigators making collections and biological observations of specific animal groups. Thus, between 1918 and 1967 at AIGhardaqa, Gohar (19~0 a,b) studied mo~uscs, fishes and other groups like scyphozoans and

crustaceans

and, i n p a r t i c u l a r ,

the biology,

ecology,

d e v e l o p m e n t and taxonomy o f a l c y o n a r i a n s .

Clark and Rowe (1971) investigated shallow water Indo-Pacific echinoderms including those of the Red Sea. Echinoderms have also been studied in the Gulf of AI-Aqabah by Clark (1952) and by Tortonese (1977, 1979) along the east coast of the Red Sea and AI-Aqahah. Fishelson (1974) worked on the ecology of the northern Red Sea crinoids. Ben Tuvia and Stelnitz (1952 and Steinltz and Ben Tuvia (1972) studied the fish populations of the Gulfs of As-Suways and AIiAqabah; Klausewitz (1959, 1967) and Sillner (1965) studied those of Sarso and the Gulf of AI-Aqabah; Scheer (1962, 1964, 1967) and Scheer and Pillai (1983) began investigating the coral communities at Bur Sudan and Abd al-Kuri and Sarso in 1962; Schmldt (1971) bega~ to work on hydroids at Eilat in 1971; Gerlaeh (1967a,b) began to study the i n t e r s t i t i a l fauna of the littoral zone especially the nematodes at Sarso in 1964, and Hottinger (i~80), Reiss, Halicz and Perelis (1974) and Zohary, Reiss and Hottinger (1980) investigated the foraminiferan populations of the Gulf of AI-Aqabah. Numerous etho-ecological studies h a v e b e e n c o n d u c t e d on t h e b e h a v i o u r o f fishes; A b e l ( 1 9 6 0 ) in 1957 at A1-Ghardaqa; Klausewitz since 1959 at A1-Ghardaqa, Sarso and Eilat; Magnus between 1962-1964 at AI-Ghardaqa and AI-Qusayr; Eihl-Eibesfeldt (1955, 1962, 1971) at Bur SUdan and the Sanganeb-Atoll; and Fricke since 1969 at Eilat. Others have been concerned with the behaviour of invertebrates, Magnus (1960, 1963a,b, 1967) and Magnus and Haacker (1968) at A1-Ghardaqa; and Schuhmacher (1973a,b,c, 1974, 1979) at Eilat and A1-Aqabah. Ormond (1974) and Ormond and Campbell (1974) worked on the Acanthaster aggregations in the middle Red Sea, and Vine (1974) has brought a better understanding of the influences of certain territorial fishes on c o r a l reef ecology. Finally, fundamental ecological research on c o r a l reefs a s an e c o s y s t e m with a wel]-baianc~d equilibrium of multiple and often complicated interactions between its components which is simultaneously influenced by a variety of abiotic factors, has advanced considerably by {:~e:

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Reefs

of the Red Sea

861

use of a variety of methods. At first, purely d e s c r i p t i v e studies of Red Sea coral r e e f s (e.g. Ebrenberg, 1934b; Crossland, 1907, 1938), were s o m e t i m e s accompanied by p r e l i m i n a r y e c o l o g i c a l o b s e r v a t i o n s like those of Klunzinger (1872). P h y s i o g r a p h i c reef zones w e r e identified, either within limited areas (Remane and Schulz, 1964; Safriel and Lipkin, 1964; Safriel G i l b o a and F e l s e n b n r g , 1 9 8 0 ; and Pot and herner-~eg~ev,1966), or of whole reef s y s t e m s ( S c h a f e r , 1967; Mergner, 1967, 1971; and Klausewitz, 1967). More q u a n t i t a t i v e b i o p h y s i o g r a p h i c zonations were made by l,oya and S l o b o d k i n (I071) and Loya (1972), Mergner and S c h u h m a c h e r (1974) and Vine and Vine (1980). Tile latest a t t e m p t s to u n d e r s t a n d the reef community as a climax c o m m u n i t y have been m a d e by r e p e a t e d q u a n t i t a t i v e analyses of experimental quadrats like that used by M e r g n e r and S v o b o d a (1977), M e r g n e r (1979), M e r g n e r and M a s t a l l e r (1980) and Mergner and Schuhmacher (1981). In addition, analyses of single groups of mobile and sessile animals w i t h i n e x p e r i m e n t a l quadrats on the reefs such as have been made by M a s t a l l e r (1978, 1979) s t u d y i n g m o l l u s c s and e c h i n o d e r m s and by F. Nobbe (personal c o m m u n i c a t i o n ) on sponges will extend our u n d e r s t a n d i n g of reef ecology. ""

T H E PROGRESS The

First

OF E C O L O G I C A L

RESEARCH

ON RED SEA CORAL

REEFS

Descriptions

Since the b e g i n n i n g of n a v i g a t i o n , coral reefs have primarily been r e g a r d e d as d a n g e r s to free passage t h r o u g h t r o p i c a l seas, while only a few people have c o n c e r n e d t h e m s e l v e s w i t h reef f o r m a t i o n and e n v i r o n m e n t a l conditions. But the earliest v o y a g e r s were f a s c i n a t e d by the corals themselves, b o t h b e c a u s e of their forms but also the myth that they could be t r a n s formed from a soft c o n d i t i o n into stone by h u m a n touch. The name "Coralium" was u s e d by T h e o p h r a s t as early as 260 BC, and then by O v i d and Plinius. However, it was not until Forssk~l (1775) that a n y t h i n g was known about Red Sea coral reefs. Ehrenberg, who was f a m i l i a r w i t h the e a r l i e r reports (e.g. C h a m i s s o and Eysenhardt, 1821 and Quoy and Gaimard, 1825), v i s i t e d nearly the whole Red Sea area and w r o t e (1834b) the first s u b s t a n t i a l descriptions of .the reefs as well as d e s c r i p t i o n s of II0 coral species (1834a). Despite the l i m i t a t i o n s caused by the inadequate chemical and physical m e t h o d o l o g y available to him and the lack of d r i l l i n g or u n d e r w a t e r o b s e r v a t i o n t e c h n i q u e s , m a n y of E h r e n b e r g ' s r e s u l t s still stand today. Thus, he n o t e d that coral reefs only occur w i t h i n s h a l l o w water areas or as fringes to v o l canic islands, a l t h o u g h he c o u l d not visit the S a n g a n e h reef near Bur Sudan w h i c h a r i s e s at all sides from several h u n d r e d m e t e r s depth as an atoll-llke formation, nor did he see any ring- or f u n n e l - l i k e reefs. He c o n s i d e r e d all Red Sea reefs to be either f r i n g i n g reefs, t a b l e - l i k e p l a t f o r m r e e f s or o c c a s i o n a l l y rows of smaller patch reefs lying far off and p a r a l l e l i n g the coast-line. He failed to observe e l e v a t e d reef p l a t f o r m s such as algal r i d g e s or surf walls c o n s i s t i n g of dead coral m a t e r i a l . E h r e n b e r g c o n s i d e r e d the l i v i n g coral layer only as the cover to dead rock, not more than 2m thick, and failed to r e c o g n l s e any t r a n s i t i o n b e t w e e n the living layer and the d e a d u n d e r lying c o r a l l l n e rock. He b e l i e v e d that the reef plates were a r e l a t i v e l y thin cover of f o r m e r isles e r o d e d away by w a v e action. In contrast, he linked the o c c u r r e n c e of the living coral formations w i t h that of the e l e v a t e d l i m e s t o n e plateaus w h i c h are found on m a n y c o a s t a l plains fringing the Red Sea. He n o t e d that over sandy or m u d d y b o t t o m s the only living corals were the fungiids. V e r t i c a l rock faces b r e a k i n g the sea did not have any coral cover b e c a u s e of the strong w a t e r t u r b u l e n c e of the h i g h surf waves. In c o n t r a s t at steep reef slopes w h e r e swash can o v e r f l o w and then flow back as a rip current, a living coral zone occurs along the reef edge. The m o s t impressive coral f o r m a t i o n s w i t h the biggest and most v o l u m i n o u s coral beads w e r e f o u n d by E h r e n b e r g a l o n g the r e e f edge. In c l o s e d basins where the w a t e r was calmer, he f o u n d s m a l l e r a s s e m b l a g e s w i t h fewer species and s m a l l e r coral colonies. He c o n c l u d e d that m o s t coral species prefer and g r o w l a r g e r in the turbulence of the surf zone. E h r e n b e r g r e c o g n i s e d the d i f f e r e n c e s b e t w e e n soft of the c o n v e r s i o n of soft coral to h a r d o c c u r r e d human being. He also p o i n t e d out that the soft

and stony corals, and d i s m i s s e d the m y t h either above water or at the touch of a surface layer of s c l e r a c t i n i a n corals is

862

H. M e r g n e r

the living animal which is covering its skeleton. atlons made 150 years ago on the development of estimated.

The great influence of Ehrenberg' s observthe modern reef ecology cannot he over-

Klunzlnger's (1870-i, 1872, 1877, 1879a,b) i n f l u e n c e was just as important and is still o f the greatest interest. His work abounded in exact biological observations, contained a great abundance of algal and animal names and above all, described the first biophysiographic zonation of a coral reef (1872). On reef zonation, Klunzinger stated: "It is not arbitrary to subdivide the reef from outside to inside into zones mostly representing different depths and horizons. Of course, there are no abrupt transitions in nature, nor here elther, where the inhabitants of the different zones encroach upon each other. But the investigator discovers these zones over and over again, each zone having its particular character, its own indicator species. New forms appear in a second zone which could not be found previously in the first, and other forms which previously occurred become more rare or disappear totally." Klunzinger (1972) recognlsed the following structural and biophysiographical zones which, in many respects are still useful today: the sea-shore with its tldal-zone characterised by O c ~ o d e saratan and Coenobita scaevola; the outer shore-zone with N erita and Gelasimus tetragonon; the inner shore-zone or eelgrass-zone with Halodule, Halophlla, Strombus ~;~bberulu,s,,ai,b,us, Clibanarius si~Datus and others; the Stylophora-zone wlth E"teromO~Pha, corallinsceans and the dominant mobile settlers Clanqu,lu,s pharaonls, gnglna mandlCamla, Alpheus edwar~li, E c h i n o m ~ t r a m a r i n a s ~, r r ~ . S ¢ O a ~ti~!a and O p h ! o c o s a e F i ~ ; and t h e w e i l ' zone e h a e a e t e r t s e d by an i n c r e a s i n g n ~ b e r Of dee~ w e i l s i n h a b i t e d by b i g g e r c o l o n i e s o f lophora ptattlla~a, T r t d a c n a and D ! a ~ a l s m ~ u m . K l u n z t n g e r c a t e g o r l s e d t h e r e e f edge w i t h lts c a v e r n system and s u r f - z o n e aS the c o r a l - z o n e i n h a b i t e d by a v a r i e t y o f AcropQea and P o c i l l o p o r a s p e c i e s t o g e t h e r w i t h N a g t l u e , Vermetus and o t h e r s , and f i n a l l y the reef slope w i t h I t s r i c h communities o f c o r a l s and f i s h e s . Some names o f zones l i k e t h a t o f t h e S t ~ 1 0 phor a -zone a r e s t i l l i n use t o d a y . K l u n z t n g e r was n o t o n l y t h e f i r s t t o Comprehensfvely r e p o r t on the f l o r a and f a u n a o f c o r a l r e e f s , b u t a l s o d e m o n s t r a t e d t h e b i o l o g i c a l and e c o l ogical interactions between the d i f f e r e n t b t o c o e n o s e s and c l a s s i f i e d them i n t o a system o f zones. He also studied the effects of the biannual extremely low equinoctial tides on the reef settlers, and the damage inflicted by coincidental extreme temperatures. During these periods

when e x t e n s i v e a r e a s o f t h e r e e f f l a t w e r e e x p o s e d , c o r a l c o l o n i e s s u f f e r e d e x t e n s i v e damage which increased either when h i g h i n s o l a t i o n c a u s e d a i r t e m p e r a t u r e s t o r i s e a b o v e 30"C, o r n i g h t t e m p e r a t u m e s f e l l b e l o w 12"C and c o l d n o r t h w t n d s b l e w . C r o s s l a n d (1911, 1913, 1935, 1938 and t 9 3 9 ) was t h e n e x t i n v e s t i g a t o r to greatly increase o u r knowledge o f t h e f o r m a t i o n and s t r u c t u m e o f Red Sea r e e f s . He p r o v i d e d b i o l o g i c a l and e c o l o g i c a l i n f o r m a t i o n on p o l y c h a e t e s and f i s h e s as w e l l as t h e c o r a l s t h e n m e l v e s , b u t h i s most i m p o r t a n t r e p o r t i n c l u d e d t h e r e e f d e s c r ! p t l o n s o f t h e Dunqunab and A1-Ghardaqa a re a s whic h supplemented the r e p o r t o f Ehrenberg (1834b) i n many ways. C r o e s l a n d (1907) s t a t e d t h a t the Sudanese c o a s t o f t h e Red Sea, a p a r t f ro m I t s m a j o r e l e v ations (i.e. > 3OOm), " h a s r e c e n t l y u n d e r g o n e s e v e r a l s m a l l e l e v a t i o n s ; t h e movements h a v e been u n i f o r m i n t h e i r a c t i o n and n o t r e c e n t l y r e v e r s e d " . He c o n s i d e r e d t h e p r e s e n t f o r m o f t h e r e e f s "due as much t o the e r o d i n g a c t i o n o f t h e sea upon t h i s e l e v a t e d r o c k as t o the growth of corals". The f o ~ m a t l o n o f f r i n g i n g r e e f s t o o k p l a c e by c u t t i n g down t h e l a n d to sea-level behind the rim of growing corals, and t h a t o f b a r r i e r reefs occurred either by d i r e c t g r o w t h o f c o r a l s upon s u b m a r i n e h l l l r a n g e s , o r by m s r l n e e r o s i o n o f p r o m o n t o r i e s , islands, and uplifted coral reefs. Battler formation by direct coral growth upon submamine hill ranges resulted In the northern ends being uplifted and forming ranges of coral.capped hills, the central parts remaining as peninsulas and islands, and the southern parts becoming the barrier reefs. C r o s s l a n d (1938) a l s o gave t h e f i r s t g e n e r a l d e s c r i p t i o n o f t h e r e e f s around t h e M a rin e B i o logical S t a t i o n a t A ] - G h a r d a q a which e s s e n t i a l l y run in broken l i n e s f ro m n o r t h - n o r t h - w e s t t o south-south-east, paralleling the g e n e r a l d i r e c t i o n o f the Red Sea c o a s t . He supplemented hls publication (1935) on new coral species, before considering the interesting problems of coral decay by boring organisms (including algae, sponges, polychaetes and mussels) by desslcation of the top and by wave action, which lead to the formation of the ring-shaped colonies of massively growing coral species; now described as "microfltol]s".

Coral

Reefs

of the Red Sea

863

C r o s s l a n d gave a d e t a i l e d d e s c r i p t i o n of the outer reefs of Abu Qalawa, Abu el F a n a d i r and A b u Sadaf; parts of the first two are living, but the third is totally dead. P r o b a b l y some p o r t i o n s of these reefs w e r e o n c e islands which have been eroded down to s e a - l e v e l and o v e r g r o w n w i t h a few feet of coral. The surface and edges of the reef flat of Abu Sadaf show n e a r l y no coral g r o w t h b e c a u s e they are e f f e c t e d by s u s p e n d e d sands and detritus, e x t r e m e l y low tides which c o i n c i d e w i t h e i t h e r cold w i n t e r night t e m p e r a t u r e s of only 14"C or hot summer n o o n t e m p e r a t u r e s of above 30"C. Coral growth is v i g o r o u s only where b r e a k e r s steadily w a s h the reefs at their outer edges or at their n o r t h e r n ends which are swept by currents, such as at Abu Q a l a w a and Abu el Fanadir. Except at its n o r t h e r n end, the reef of Abu Sadaf is d e c a y i n g and seems to be d e a d since the last change in the sea-level. C r o s s l a n d c o m p a r e d the flat b o t t o m s of Abu Shaar and M a b a h i s s Lagoons with the features of an atoll lagoon. He d i s c u s s e d the two possibilities: that either the shoals r e s u l t e d from the r e c e s s i o n of coral a s s e m b l a g e s which had o r i g i n a l l y e x t e n d e d to and formed the steep cliff, or they e x i s t e d before the coral g r o w t h and the coral was still e x p a n d i n g and had not r e a c h e d its m a x i m u m g r o w t h limits. The four small harbour reefs were d e s c r i b e d by C r o s s land as the inner reefs. T h e s e are l o c a t e d between the B i o l o g i c a l S t a t i o n and Shah el Abyad, the s o - c a l l e d White Reefs w h i c h are a series of e x t e n s i v e sandy s h a l l o w s s c a t t e r e d w i t h corals~ alcyonarians and sponges, f r o m w h e r e the prevailing n o r t h - w e s t winds bring in m u d d y water. T h e s e h a r b o u r reefs w e r e c o n s i d e r e d to be a time series with the North H a r b o u r Reef being embryonic, the central two as a d o l e s c e n t (South H a r b o u r Reef) and adult (Crescent Reef), a n d the m o s t southerly, the S o u t h e a s t Reef, as senile. C r o s s l a n d based these d i f f e r e n t i a t i o n s on c h a r a c t e r i s t i c s of the r e e f coral c o m m u n i t i e s such as the r e l a t i v e p r o p o r t i o n s of living to dead, a n d of s c l e r a c t i n i a n s to a l c y o n a r i a n s . The shore r e e f was in a late stage of decay, and c o n s i s t e d of an e r o d e d s a n d s t o n e or r e e f p l a t e f r o m w h i c h p r o t r u d e d a few places of p l e n t i f u l coral g r o w t h along its rim. Crossland described some simple m o n o s p e c i f i c communities c o n s i s t i n g of n u m e r o u s colonies of G a l a x e a f a s c i c u l a r i s or of L o b o p h ~ l l i a cor~mbosa. He d i s c u s s e d the e c o l o g i c a l r e l a t i o n s h i p b e t w e e n corals and a l c y o n a r i a n s , w h i c h p r o v i d e s an e x c e l l e n t index of reef growth; since w h e n a l c y o n arians are d o m i n a n t reef g r o w t h is nil, if not negative.

Structural

and bioph~siographic

zonation

a) G e n e r a l Remarks a n d M e t h o d o l o g y : The g e o l o g y and g e o g r a p h y of Red Sea reefs have b e e n d i s c u s s e d by Ruppell (1829) in the G u l f of Ai-Aqabah, W a l t h e r (1888) along the Sinai coast, M a c F a y d e n (1930) at A s h r a f i a n d Jubal I s l a n d s in the n o r t h e r n Red Sea a n d Farasan and K a m a r a n I s l a n d s in the s o u t h e a s t e r n , G u i l c h e r and B e r t h o i s (1955) at F a r a s a n Islands, Nesteroff (1955) also at F a r a s a n Islands, Friedman (1966) along the Sinai coast, Einsele, G e n s e r and W e r n e r (1967) in the s o u t h e r n exit of the Red Sea, Nit (1971) at the D a b l a k A r c h i p e l a g o , Guilcher (1979) at the S i n a i coast, and Gabrie and M o n t a g g i o n i (1982) at the Jordan coast of the G u l f of A1-Aqabah. Von R a n s o n n e t - V i l l e z (1863) p u b l i s h e d the first u n d e r w a t e r p i c t u r e s of reefs p a i n t e d w h i l e s u b m e r g e d in a diving hell. None of these r e p o r t s are of direct i n t e r e s t to the reef e c o l o g i s t . T h e s u m m a t i o n of a b i o t i c and b i o t i c f a c t o r s i n f l u e n c i n g an e c o s y s t e m d e t e r m i n e the s t r u c t u r e of its b i o c o e n o s e s . N o r m a l l y these persist in a w e l l - b a l a n c e d e q u i l i b r i u m of the s y n e c o logical relations b e t w e e n their i n d i v i d u a l m e m b e r s and groups. Enviromental factors w h i c h are m u t u a l l y a n t a g o n i s t i c d e t e r m i n e d e p e n d i n g on w h i c h is l o c a l l y m o r e important, the f o r m a t i o n of zones b o t h in a h o r i z o n t a l or v e r t i c a l series. In coral reefs, the horizontal z o n a t i o n is m a i n l y the r e s u l t of v a r i a t i o n s in the i n f l u e n c e of surf and its swash, w h e r e a s the v e r t i c a l z o n a t i o n is i n f l u e n c e d by t u r b u l e n c e and r i p c u r r e n t s c o m b i n e d w i t h the light gradient. T h e r e f o r e , z o n a t i o n is an i m p o r t a n t e x p r e s s i o n of the c o m b i n e d a b i o t i c a n d biotic influences, of the s y n e c o l o g i c a l i n t e r a c t i o n s b e t w e e n their b i o c o e n o s e s and of their actual composition, condition and diversity. However, each single zone can be c h a r a c t e r i s e d by c e r t a i n i n d i c a t o r s p e c i e s w h i c h are e i t h e r very c o n s p i c u o u s or n u m e r i c a l l y dominant. Hence, the i m p o r t a n c e of z o n a t i o n to coral reef e c o l o g y was r e c o g n i s e d at a r e l a t i v e l y early stage, with either structural or b i o p h y s i o g r a p h i c z o n a t i o n or both being e m p h a s i s e d a c c o r d i n g to the p a r t i c u l a r aims and i n t e r e s t s of each investigator. A d i s c u s s i o n of the q u a l i t a t i v e and q u a n t i t a t i v e m e t h o d s and r e s u l t s on r e e f z o n a t i o n in the Red Sea f o l l o w s (see also S t o d d a r t and Johannes, 1978).

H. M e r g n e r

864

Scheer (1960, 1967) p u b l i s h e d the first report on m e t h o d s useful for reef r e s e a r c h when he d e s c r i b e d both a transect and a p h y t o s o c l o l o g i c method. Loya and Slobodkin (1971) u s e d a plotless t r a n s e c t - 1 1 n e method, and N e r g n e r and S c h u h m a c h e r (1974) studied the A I - A q a b a h reefs by a n a l y s i n g two b r o a d t r a n s e c t strips. Then N e r g n e r and his co-workers (1977-1981) used q u a n t i t a t i v e a n a l y s e s of 5x5m q u a d r a t s in s t u d y i n g the coral reefs of A1-Aqabah and Bur Sudan (see below). L o n g - t e r m i n v e s t i g a t i o n s have also been done using manned Underwater research stations (Cousteau, 1964; -and Fricke 1977); at g r e a t e r depths investigations need research submarines such as Fricke's 'GEO' (1983).

b) S t r u c t u r a l zonation: The structural zonation of Red Sea coral reefs has been studied by using s p e c i f i c animal groups as indicators. Abel (1960) not only described the behaviour of the fish f a u n a near A l - G h a r d a q a but also the structure and zonation of the coral reefs of the h a r b o u r series. .... ,~

~ter

o~

Fig.3.

T h r e e - d i m e n s i o n a l diagram i l l u s t r a t i n g a typical coastal fringing r e e f of the m i d d l e Red Sea, s h o w i n g the r e e f structuare and zonation a n d the m o s t important e n v i r o n m e n t a l conditions u s i n g hydroid growth as i n d i c a t o r (after Nergner, 1967).

M e r g n e r (1967) s t u d i e d the e c o l o g y of reef h y d r o i d s on both sides of the Red Sea. Extensive p r e l i m i n a r y i n v e s t i g a t i o n s w e r e made on the s t r u c t u r e and settlement of the r e e f s by analysing the

structural

zonatton

of

six

coral

reefs,

three

on

the

west

slde

and

three

on

the

east

side. T h e s e reefs w e r e c a t e g o r i s e d a c c o r d i n g to their location with respect to the open sea and their age, either as narrow r e e f fringes or as typical coastal fringing reefs, or as p l a t e a u - l i k e b r o a d e n e d r e e f s with l a g o o n s behind their rim. The typical fringing reef of this series (Fig.3) had a broad reef flat w h i c h sloped gently down from the shore. Near the top of the shore was a nearly barren m u d d y a b r a i d e d zone which dried out periodically; this barren zone gave way to a uniform seaweed zone which in turn was succeeded by a m u l t i f o r m well zone with n u m e r o u s small pools. Only where there was plenty of water movement near the reef edge, was "living reef" formed. The band of living reef was steadily growing outward so that not only did the "dead reef" behind c o n t i n u a l l y broaden but also ~he talus sII~e

Coral

Reefs

of the Red Sea

865

of debris b e n e a t h the r e e f cliff became c o n s t a n t l y higher. The intensity of w a t e r e x c h a n g e is the c r i t i c a l e n v i r o n m e n t a l factor because it affects the supply of o x y g e n and nutrients, the balance of t e m p e r a t u r e and salinity, as well as the sedimentary r e g i m e and carbon d i o x i d e concentrations. The most v i g o r o u s coral growth is found at the reef edge and on the u p p e r slope, where a variety of densely p o p u l a t e d m i n i a t u r e blotopes exist, each with d i f f e r e n t ecological c o n d i t i o n s and inhabited l)y d i f f e r e n t a s s e m b l a g e s of species. Schifer (1967) studied the b i o f a c i e s s t r u c t u r e of reefs at Sarso, and Klausewitz (1967) e x a m ined the p h y s i o g r a p h i c a l z o n a t i o n of the reefs along the coasts of Sarso and Sindi Sarso w i t h the a n a l y s i s of three profiles which included twu steep Coast sections, one with and one w i t h o u t e r o d e d e u ] i t t o r a l p l a t f o r m and a sand beach. The fish fauna and the most c o n s p i c uous invertebrates and algae were identified and their d i s t r i b u t i o n and z o n a t i o n studied. Klausewitz (1967) found both isles to be raised subfossil reefs with the recent reefs being based on the old eroded platforms. The littoral areas of the isles were of late T e r t i a r y or early P l e i s t o c e n e c o r a l l i n e origin and showed a number of ancient sea levels r e s u l t i n g either from tectonic or e u s t a t i c changes in the sea level. He mapped part of the coastal a r e a s h o w i n g the s t r u c t u r a l z o n a t i o n of the sandbay of Sarso, the first s e m i - s c h e m a t i c m a p p i n g of structural z o n a t i o n c o m b i n i n g lists of the fauna of each zone. % of full d a y l , g h t current

st,ongl,ght

zone

r s ui, nf n ezone

long,eel c u r r e n t I~teral w ~ t e r d i s p l a c e m e n t ,revJll~n9 horizontal oscillation in c o m p l i c a t e d figures

, ~

: ~

,

~

'

reef.

~lrf

rip ( u r r e n l $ o~O,tal movement preys;ling vertical OSCill.~tion

,-

:

¢OrAIL zone

( o t a l d e t r i t u s , s J n d and mud; Knolls: COral t u c k flat w i f h Knolls littorel

.....,.o

fore r . e t r I upper

.f~ • i ~

coral rubble sorer

i I w#ter I turbulence j I

. - ' ._; . ~ - : - ~' . ~ . : . ' -' : . ' . ' . '~- ' - ' : ~

',; '..~~~11/I//111/,,~ ~ / / / / / / / / ~ ~///////////////////~ Fev~,-~JNs z GAIatxeaa zone

outer

~

"

~

,

zo.e

su,f

o~d~adc~ral¢ock

surf

elect ~a~e,, d e c r e a s , n g t o w a r d s $ea - s h o r e mor~ or le~s o v e r l a p p e d by lon~lreef

spray

zone

hya run.

wea~ ~ r,p current~

spray

~

I mast/), c.~lm waCer

- • : :- ° ~ . :

.

.- ~ ~,~ .....................

Tubipora musica zone

IHostly living¢~at~

~i~nh fho~e,

zone

t

0 ~ ' ~

a b r# ided dead coral rock ¢~etritu$ w~tll~n the holes

coral

outwar¢~ IN%-f buttress: c e e ~ p l a t f o r m i r e e f MOpe :et~e zone ',

~lreef : ....

~

~

,,,

~

.:

~:

,~. . . . . . . . . . . . . . . . . . . . .

StWophorA pJs tillatA

or

~

zone.

de~d g.oit c.~.a.l. heads. P/Atygyra- m,croatoll lagoon

~

~

iiii

c~Annel

~

shore

.t .o. n. .e. s s~And*

ZOne

sir.

sublittoral

I ...... ...'1 Pig.4.

....... . .

Io,

,.o.

;~s:,_

aOo,s¢,O-4O;.

-I-1 ....... ,-,&

T

,-,.~

,

.,

P r o f i l e t h r o u g h the f r i n g i n g reef of Eilat, showing the c h a n g e s o c c u r r i n g a c r o s s the shore in the d i s t r i b u t i o n s of light intensity, h y d r o g r a p h i c zones, w a t e r m o v e m e n t s , b i o p h y s i o g r a p h i c zones, substrate type, s t r u c t u r a l zones, l i t t o r a l zones, and w i d t h and d e p t h of the d i f f e r e n t zones in metres. Black arrows indicate the surf and its swash. Black b r o k e n arrows indicate rip currents; r o u n d e d arrows, v e r t i c a l o s c i l l a t i o n s , and white arrows, l o n g r e e f currents. htl, h i g h tide level; mtl, m i d d l e tide level; ill, low tide level. (after M e r g n e r , 1971).

c) Qualitative biophysiographic zonatio,*: M e r g n e r (1971) d e v e l o p e d this m a p p i n g a p p r o a c h w i t h his e x t e n s i v e semi-schematic d e s c r i p t i o n of a transect through the n o r t h e r n f r i n g i n g r e e f of Bilat w h i c h i n c l u d e d d a t a on the a b i o t i c c o n d i t i o n s in each of the b i o p h y s i o g r a p h i c zones (Pig.4), i n c l u d i n g light intensity, w a t e r movements, and substrate. He i n d i c a t e d the d i s t r i b u t i o n s of the ten m o s t i m p o r t a n t coral species and the names of the i n d i c a t o r species, a n d the w i d t h and d e p t h r a n g e of the d i f f e r e n t zones. The pattern and d i r e c t i o n of the d o m i n ant w a t e r m o v e m e n t s , such as surf, swash, rip currents, longreef current, waves and swell

866

H. M e r g n e r

were indicated. Thus, the factors of each reef zone.

19TI)

have g i v e n

the

first

scheme m a k e s it possible to d e t e m m l n e The q u a l i t a t i v e analyses of K l a u s e w l t z

accurate

impression of the structure

the abiotic and biotic (1967) and M e ~ g n e r (1967,

and b i o p h y s l o g r a p h i c

zonation

of a typical Red Sea coastal ~eef, but only f r i n g i n g reefs and their formations were studied and other reef types such as barrier reefs are yet to be analysed. Vine and Vine (1980) i n v e s t i g a t e d some of these other reef types by analysing 30 profiles along the Coast of the Sudan between Dunqunab and Sawakln. S e c t i o n s of each reef were drawn to scale, and the locations of the important m e m b e r s of the s e s s i l e fauna and flora indicated; special a t t e n t i o n was paid to the stony c o r a l s , g o r g o n a r l a n s and sponges. In addition, a checklist was provided of 20~ fish species t o g e t h e r with r e l e v a n t biological and ecological data on their v e r t i c a l and horizontal d i s t r i b u t i o n at each site. Thus, Vine and Vine (1980) have greatly e n h a n c e d our knowledge of the S u d a n e s e coral r e e f s and have d e m o n s t r a t e d their v a r i a b i l i t y and r i c h n e s s as blotopes.

d) Littoral zonation: The intertidal zonation of ~ed Sea shores has been described by Magnus (1960, 1963a,b, 1967) and Magnus and Haacker (1968) on the shores near A i - G h a r d a q a and ~lQusayr in connection w i t h their i n v e s t i g a t i o n s on the e c o l o g y and ethology o£ a variety of littoral species. The s u p r a l i t t o r a l zone he defined as c o n s i s t i n g of an elevated Pleistocene reef which separated land from sea by a cliff and a sand zone, the eulittoral, as the broad wave-cut terrace with its isolated blocks of former cliffs and a tide-pool zone; the final zone was the ~ecent reef. Remane and Schulz (196g) d e s c r i b e d the fauna of the shores of A i - G h a m d a q a with special attentlon being paid to the m l c r o f a u n a . They found that the f l o t s a m in the sup~allttora! was

i n h a b i t e d by v e r y few s p e c i e s , b u t a l l t h e o t h e ~ z o n e s w e r e i n h a b i t e d by a r i c h f a u n a . Thus high tide-pools of the cliffs and t h e c o a s t a l g r o u n d w a t e r o f t h e s a n d y a r e a b e l o w t h e cliffs, the clumps of sand-collecting a l g a e n o t a b l y t h o s e of t h e r e d a l g a D i ~ e n i a S~mpiex within the eulittoral, and t h e s a n d gl~ound o f t h e s u b l i t t o ~ a l bottoms all contained rich

the

and varied faunas. T h e i r results are c o m p a r a b l e w i t h those stitial subsoll fauna of the sand beach of Sarso Island.

of G e r l a c h

(1967)

on the

inter-

Safrlel and Lipkin (1964) studied the intertidal z o n a t i o n of the rocky shore of Eilat. USing transects they i d e n t i f i e d 7 zones each inhabited by c h a r a c t e r i s t i c organisms, notably algae, g a s t r o p o d s and barnacles. The z o n e s w e r e termed as a s e l d o m aul~ae~ged "terrestrial zone", a "littorlnld zone" d o m i n a t e d by T a g , S ! U S 8ubnodOm:~a and L i ~ o r ! n a n o v ~ z e ~ d i ~ e , a "chthama i l d , o n e " with a .mall C h a ~ , I p h O ' p - - ~ i ~ ' , ' " ~ e t r a ~ l l t a .o.." with ...........

r u ~ o t i n c t a , and t h e c h i t o n A c ~ t ~ l e v ~ ' a haU~i, a " S ~ t a zone" wil mentOBa, and below t h e s e f i v e z o n e s w h i c h a r e r e g u l a r l y e x p o s e d a t low t i d e was a " R h o d o p h y t a S e r P U l O r b i s zone d o m i n a t e d by S e ~ p ~ ! p r b i s ~ m o p e p t u s and o n l y e x p o s e d d u r i n g low s p ~ i n g tides and a "~eef-forms" zone. Safrlel, Gilboa and P e l s e n b u r g (1980) examined the distribution of intertidal m u s s e l s on the rocky shores of Sinai and the Suez Canal. Deeper-llving benthic organisms were studied by Pot and L e r n e r - S e g g e v (1966). Pishelson (1970, 1971, 1973a,b, 1974) studied the reefs of the Gulf of A1-Aqabah and e x t e n d e d the b i o p h y s i o g r a p h l c z o n a t l o n of the shore area out into the lagoon and on to the reef platform. He examined the different biotas O C C U r r i n g a l o n g the Sinai coast and on the Dahlak Archipelago (sandy and muddy bays, vertical c l i f f s of the fossll coral reefs, and m a n g r o v e fox,nations). He found the f o l l o w i n g communities: in soft bottoms, an "Ocypoda saratan D o t i l l a s u l q a t a c o m m u n i t y " i n h a b i t i n g the sandy s u p r a t l d a l and shallow i n f r s t i d a l zone; a " H i p p a p l c t a - Nactrs o l o r i n a community" p a r a l l e l t o the preceding community but on steeper

shores

with coarser

sand

and g r a v e l ;

a "Pt~hodera

flays

- ~Ld!an~hgs kosei~ensis

community"

on the c a l c a r e o u s - m u d d y sediment of the lagoon; a ,H~lophl1& ~tIpulacea , Asy~mnetron(luca~num?) community" i n h a b i t i n g g e n t l e slopes e x t e n d i n g from d e p t h s o f 2-5m to about 4Om where there were muddy bottoms c o n t a i n i n g a high percentage of o r g a n i c detritus; and, an "Op_e_rcu!iina galmardi - T u r r i t e l l a terebra co~aunity" on gravel and broken shell substrates which were m i x e d with silt and mud from 30-40m down to 200-26Om. F i s h e l s o n discovered a " Tectarius ~tus - T e t r a c l l t a s q u a m o s a r u f o t i n c t a community" from the high supratidal area inhabiting littoral rocks; and a "Gena vamia E c h ~ n o m e t r a m a t h a e l c o m m u n i t y " below the infratidal, on dead coral rock on m u d d y sediment. He gave some e c o l o g i c a l information on the mangrove areas of the Dahlak A r c h i p e l a g o and the southern Sinai Peninsula. Fishelson's work also c o n c e r n e d problems of pollution and low tide damage to coral reefs and thei~ communities (1970, 1973a,b) and on the stability of marine e c o s y s t e m s (1977) which will be discussed below.

Coral Reefs of the Red Sea

867

Two m e t h o d s have proved to be particularly successful for q u a n t i t a t i v e l y e v a l u a t i n g the zonation of Red Sea reefs, the t r a n s e c t - l i n e m e t h o d and the t r a n s e c t - s t r i p method. The first involves the use of a t r a n s e c t - l i n e with c r o s s - l i n e s at f i x e d distances. All coral c o l o n i e s o c c u r r i n g along the cross-lines are measured. T h i s m e t h o d allows the rapid a n a l y s i s of extensive reef areas and makes evaluation of each species easy r e l a t i v e to the other species and simplifies the problem of the d i f f e r e n t i a t i o n b e t w e e n corals from horizontal and those from vertical zones (l,oya, 1978). The second m e t h o d involves the correct scaling and m a p p i n g of each coral colony within a broad transect-strip. Its use in extensive reef areas is very demanding in time and effort and can create d i f f i c u l t i e s in the d i f f e r e n t i a t i o n b e t w e e n horizontal and vertical zones; m a t h e m a t i c a l a n a l y s i s of the data is equally time consuming. However, this latter method is more easily u n d e r s t o o d and easier to reproduce s u b s e q u e n t l y . It results in a clear visual r e p r e s e n t a t i o n of the s e t t l e m e n t s t r u c t u r e s and b i o p h y s i o g r a p h i c zonation. It is, therefore, the p r e f e r a b l e m e t h o d to be used as a basis for subsequent research. Both methods have their uses as will be i l l u s t r a t e d by typical e x a m p l e s from the Gulf of Ai-Aqabah.

e) Q u a n t i t a t i v e b i o p h y s i o g r a p h i c zonation: Loya and S l o b o d k i n (1971) published their desc r i p t i o n of the coral reefs of Eilat, w h i c h Loya (1972) f o l l o w e d up with a q u a n t i t a t i v e study of the community structure and diversity of h e r m a t y p i c corals. Loya and Slobodkin (1971) studied three transects all t o g e t h e r involving 84 cross-lines, each lOm long. They found 97 s c l e r a c t i n i a n species b e l o n g i n g to 40 g e n e r a and 13 families, among them the dominant species of seven zones e x t e n d i n g from the shore down to depths of about 30m including the lagoon, the rear reef and the r e e f flat, a " S t ~ l o p h o r a p i s t i l l a t a zone"; for the upper reef slope, a " M i l l e p o r a d i c h o t o m a zone"; for the u p p e r fore reef, an "Echinopora gemmacea zone"; for the patch reef r e g i o n (the m i d d l e fore reef), a m i x e d "Acropora hemprichi - A. v a r i a b i l i s zone"; and for the lower fore reef, a "Porites l u t e s zone". Each species was c l a s s i f i e d a c c o r d i n g to its r e l a t i v e a b u n d a n c e in the d i f f e r e n t zones. The average number of species r e c o r d e d per c r o s s - l i n e i n c r e a s e d with depth, from 11-15 species in the reef crest r e g i o n to 26-29 species in the "Porites lutes zone". This latter zone and the "Millepora d i c h o t o m a zone" were the r i c h e s t in numbers of c o l o n i e s and s u r f a c e - c o v e r a g e by living corals with 85% and 75% s u r f a c e - c o v e r a g e r e s p e c t i v e l y ; the A c r o p o r a h e m p r i c h i - variabilis zones w i t h 20.3% c o v e r a g e were the poorest. Loya and S l o b o d k i n d e m o n s t r a t e d that the line-transect m e t h o d a v o i d e d most p r o b l e m s of b o t t o m t o p o g r a p h y and s i m p l i fied field recording procedures. It also proved h i g h l y e f f i c i e n t in i n f o r m a t i o n r e c o r d e d per time spent underwater. Loya (1972) expanded these results by a n a l y s i n g the community structure and the species diversity of the hermatypic corals i n t h e same r e e f s . He u s e d a v a r i e t y of several diversity indices, the species count, the S i m p s o n index and the S h a n n o n - W e a v e r index, and c o m p a r e d them throughout the study areas. D i v e r s i t y (H) i n c r e a s e d from an a v e r a g e of 2.0 at the reef crest to 3.0 in the "Porltes lutes zone". Even h i g h e r d i v e r s i t y values were found by M e r g n e r (1979) in the reef lagoon of the A i - A q a b a h reefs, and by M e r g n e r and S c h u h m a c h e r (1981) in the middle fore reef. Loya (1972) a s s u m e d that e x t r e m e ablotic c o n d i t i o n s on the r e e f flat l i m i t e d the diversity and a b u n d a n c e of the coral colonies, and r e s u l t e d in the s m a l l e r size of the colonies and their lower c o v e r a g e c o m p a r e d to the deeper reef. The d e c r e a s e of light intensity with respect to depth was not seen as i n h i b i t i n g the a b u n d a n c e of the coral species, but as a significant factor in c a l c i u m c a r b o n a t e d e p o s i t i o n by the s c l e r a c t l n i a n s . The lower species diversity and coverage of level reef areas compared to steep ones is caused by the greater accumulation of sediments. Finally, L o y a made p r e d i c t i o n s concerning sedimentation effects on different c o r a l - g r o w t h forms, and the r e l a t i v e success of d i f f e r e n t c o r a l species in invading different r e e f zones. In areas of h e a v i l y s e d i m e n t a t i o n b r a n c h e d c o r a l species will have a selective advantage over massively growing species unless the later possess cleani n g mechanisms. S t y l o p h o r a p i s t i l l a t a was s u g g e s t e d to be an o p p o r t u n i s t i c species, w h i c h is able to invade t e m p o r a r i l y vacant niches. M e r g n e r and S c h u h m a c h e r (1974) u s e d two t r a n s e c t - s t r i p s , each 2 0 0 m long and 20m wide, extending from the shore to the fore reef in about 3Om depth in s t u d y i n g the coral r e e f s of AIA q a b a h (Fig.5). The r e l a t i o n s h i p s of s t r u c t u r a l s m d b i o ~ s l o E r ~ c r e e f z o n e o t o abiotic environmental factors were c o n s i d e r e d and the d i f f e r e n t reef a r e a s d e s c r i b e d (Fig.6). The important reef structures, reef zones and coral colonies were d r a w n to scale and mapped. W a t e r depth, substrate, temperature, i l l u m i n a t i o n and w a t e r m o v e m e n t w e r e recorded. In all, about 200 common and dominant species were collected, and their distributions p l o t t e d t o g e t h e r with

868

H. Mergner

Flg.5.

Schematic diagram of t~e showing the location of and Schuhmacher (1974); (centre), and the second shown are the positions in the mlddle fore reef

r e e f a r e a 6km s o u t h o f A q a b a h a r b o u r (left) the two transect-strips studied by Mergner the first crossing the coastal fringing reef the lagoon fringing reef (eight). Also of the test squares studied, among them U-7 a n d L - I In t h e l a g o o n ( a f t e r Nergner, 1981).

other data. Variations in the indicator species which characterised the biophysiographlc zones depended on patterns of water movement. This basic factor also cofltrolled other ecological paraweters such as food, oxygen supply, and the temperature and salinity gradients between fore reef and shore. The differe~ces in the shapes of the two study reefs were explained on the basis of a "reef development cycle" - a hypothesis applicable to fringing reefs where sea level is relatively constant. It i8 based on the fact that only a small surf-influenced area of "living reef" is needed to compensate for reef destruction. The exact mapping of the structura] zones, the btophysiographic zones and the coral assembiages could easily be used as the basis for a mathematical analysis of community structure and zonation; such analyses are planned by Nergner and his colleagues. Head (1980) used a siml1at mapping approach tn his work on the ecology of corals in the Sudanese Red Sea.

CoPal

-.-~,

Reefs o f

~,: = . . ~ : . - ~ . ~ ~ : : - ~ : ~ < ~ : . ~ : ~ i . . ! < ~ i ~ : . : : ~ . i : i ; : ~ i : . s ~ ~ ) ~ .-~-:::::-~.:~i~i?~i~:>~ ~::~i ~ : - : i ! ! ~ : : : : : i : : ' ! ~ . ~ . ~

the

,

869

Sea

.....

~

'

Red

"

~,~.~._~-~

. . ,

!

•"

......

~ , ,"-:- :-.' . . ................. "~0:. ~ :- . . . . . ~ .<:.~.:~::.:-i:~::: ::~:? ::. ............ " .- .~ :~. -c, ~, , i ~.:...~. , ~ . . + . .. .. . . . . . . .: : : : .: :: : . :.................. :..-.:~ . . •. ............... ~ - ' . ~ .:..~...,.., . . . . .• . . .

'

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.

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~

.

.

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.

.

.

.

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.

.

E~2dead~ (reef flat) shore c~aler zone c~anne)

spray shore surf

calm

longshore

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current



+

~.: ~

,



:

swash



', _

and

1+

~

+ +

* ,," ~ ' W

{ore

l e , oded

reef

Iongreef

+ ~. +::o .,;;',+.`+~. n

e

"

-. ~+

o

strudures:

- - p l a.re, tform

tide lines:

--level

water movement :

high fide

~

- - - - l hast, ine

crater'-~ ,ik.p.,

low fide

mean tide --level

wind and sur face sud waves 4bill c uerent

deep and 4'W%;p current

..... level

Fig.6.

O

"

~ l = ~ ° ~ n°genic

plants:

® , o coral . . t rod<

micro atolJ

0

middle

fo[e

current

~ ~

'

a)ternatlng long reef c u r r e n t

:-e:.--T

..,,'. ~-:.+...

~

i

~

~

reef

loose Co,a] £Ommunif~

!

:

i

:

+

:

~

~C~.:<::.:'.

~ea: . . . . .reef . . . . .p l.a.t .f o.r.m. . . . . . . . .reef . edge reef

weak orbilal oscillation

otyf~b~ li~MUIvl

zone ........boundary

~

A

O a~-

..............................

coral

reef area )

~ J 2 l ~ :

shore z o . e reef lagoon ( eroded a,ea of the r e e f f l a t ) coarse ~ a c h shore sand rock channel eetgrass zone a l g a l zone soft coral zone microatoll zone shore spray surf calm longshore current and Swash

I:~beach

to{met

Oute, p,nnacfe

r~p currents

~> ~ :., ~

,.%.

'e

,

; ®;

reef surf

upper

•-) . . . . . • . . ~-'.~.~ . . . . . . •

.:

.

m,ddle pinna]de

'°:| ' ~

., ~ .• ~ . : o . - . . r ; . "~ : o . ~ ' . - . . ) - . . - . ~ e

.

-

shore zone coarse ~ a c h sand rock

~.-'~!~,'o-'::'+

.-I.?:'~~., ~ . ~:..-

' "~'':

and slope

wit. canal system

back flow through the canal system

swa sh

~eef surf"

~

s,....... ,s: l l ~ . ~ , ~ . . m e soft corals :

~ ~

others :

~/~ille~ora

[itophyton

Io.greef tip current currents

Sargas-

- - podium ~,~ oea zone ~

(I dieMa. S;nularia (~1 ~.~ophyttlm

fore reef

~

Halodule

maSSively 9rowln9 corals

~ Xenia, Heteroxenia

Tetra dita

r~di(hofom~ ~ s q u a m o s a

Comparison between the structural, hydrographic and blophysiographic zonatlon along the two transect-strips through the fringing reef 6km south of Aqaba harbour (after Mergner and Schuhmacher, 1974).

Quantitative analysis of population dynamics a) General remarks and methodology: All the studies cited so far with the exception of the behavioural studies have used a qualitative descriptive approach and have taken no account of the temporal changes in the communities. However, a better understanding of the interactions between the different biocoenoses and their constituent members, and of the complicated structure of coral reefs can only be achieved by studying the dynamics of the reef community. Quantitative analyses of the seasonal and permanent changes in the algal and faunal communities ape needed to supplement previous one-time studies. This can be done best by long-term studies of selected quadrats in critical reef zones. Scheer (1960, 1976b, 1978) and Mergner and Scheer (1974) first applied phytosoclologlcal methods to reef studies at Addu Atoll, Maldlves. They used 5xSm quadrats to derive data on abundance, dominance, coverage degree and sociability of the coral species. Mergner (1979, 1980) and his co-workers were the first to use similar methods in the Red Sea. Two experimental areas were selected, one, called L-l, in the reef lagoon south of AI-Aqabah, the s e c o n d U-7, in the fore reef of the same reef. A long-term quantitative analysis of the seasonal changes of the macrobenthos community was carried out at L-I (Mastaller, 1979; Mergner, 1979, 1981; Mergner and Mastaller, 1980; Mergner and Svohoda, 1977; and Nobbe, personal communication). A slmila~P analysis of the changes of the coral community at U-7 has been carried out (Mergner, 1980, 1981; Mergner and Schuhmacher, 1981). b) Seasonal changes: In the lagoon, the L-1 experimental monotonous and yet more than 2000 algal colonies and 2200

This and

astonishingly 10

faunal

rich stock

phyla.

The

consisted

quantitative

area (Fig.?) o f o n l y 25m appeared individuals of macrofauna occurred.

of 237 species belonging data

provided

information

to 192 genera on

the

from 4 algal

seasonal

changes

870

H. M e r g n e r

in abundance, d o m i n a n c e , and species c o m p o s i t i o n , and w i t h the m a p s provided specifically on c h a n g e s o c c u r r i n g in the s e t t l e m e n t s t r u c t u r e of the biocoenoses.

Fig.7.

information

Map o f t h e t e s t area L-1 in thereef l a g o o n 6km s o u t h o f A q a b a Sarbour illustrating the patterns of settlement of the macrobenthic flora and fauna and their seasonal fluctuations (after Mergner, 1981).

A seasonal cycle occurred both in the algae and in some cnidamians. At the end of October nearly all the algae had disappeared. At the b e g i n n i n g of January, a new algal stock had appeau-ed w h i c h went through a s t r i k i n g specles s u c c e s s i o n . In February, there w e r e 2037 colonies b e l o n g i n g to 22 specie8, with a total c o v e r a g e of 26%. These m a c r o b e n t h i c algae d i s a p p e a r e d g r a d u a l l y a g a i n between early s p r i n g and late summer, as a result of the e f f e c t s of g~azers, e p i p h y t e s and natural decay processes. In October, 83 s c l e r a c t i n i a n colonles and 161 soft coral c o l o n i e s occupied about 6% of the area. By March, 34 colonies, i.e. about 0.5~ coverage, d i s a p p e a r e d because of grazing by sea urchins. Then r e c o l o n l s a t i o n o c c u r r e d by 104 colonies, i n c l u d i n g 65 S t ~ l o p h o r a p i s t i l l a t a and 32 Xenia colonies, with a total coverage of 0.6%. So in March there were ~5~ c o l o n i e s with 6.6% areal coverage. But a n a l y s i s showed that only 10% of ~ e y ~ S t y l o ~ h ( ~ colonies w h i c h settled on algae-free substrate survived over a y e a r (Mergner 1979, ]981). The

seasonal

to those

of

changes

the

in

phytal.

the

abundance

The

reef

of

lagoon

the

mobile

provided

macrofauna

suitable

showed c l e a r relationships and hiding place~!; f'or'

substrates

Coral Reefs of the Red Sea

871

a rich and s p e c i a l i s e d m o l l u s c a n fauna; in a sample of 1147 individuals, 113 species from 77 genera were i d e n t i f i e d and t h r o u g h o u t the year the mollusc community had a mean species diversity index (H) of 3.5. There was a steady decrease in the total population from February (I00~) to June (79.2~) to N o v e m b e r (61.2%). This c o i n c i d e d with the decline of the phytal community through early summer to its total d i s a p p e a r a n c e in the late autumn, indicating a r e l a t i o n s h i p between the decline in abundance and diversity of the m o l l u s c s and the seasonal decline of the phytal. During this period, the h e r b i v o r o u s and detritophagous species decteased by 40~, but the c a r n i v o r o u s species only by 20%. T h e r e was a migration of i0 h e r b i v o r ous species into the "Halodule uninervis seagrass zone", and another by 5 species into the "micro-atoll zone". T h e r e were similar changes in the echinoderm community in which the adult population arose b e t w e e n O c t o b e r and February from 79 to 196 and the juveniles from 0 to 62. In February, 77~ of adult sea urchins and 85% of the juveniles were h e r b i v o r o u s species. The probable causal r e l a t i o n s h i p between the m i g r a t i o n of the echinoids and algal growth during w i n t e r was indicated by the conspicuous algae-free areas which surrounded the hiding places of D i a d e m s setosum. The q u a n t i t a t i v e a n a l y s e s of the sity of the m a c r o b e n t h l c groups parameters lay w i t h i n the normal old g e o m o r p h o l o g i c a l age of the increases of sessile m a c r o b e n t h i c

seasonal changes at L-l, in abundance, dominance and diverb e t w e e n autumn 1975 and autumn 1977, indicated that these range of f l u c t u a t i o n in this climax lagoon community. The lagoon f r i n g i n g reef and linking of seasonal decreases and groups like algae and cnidarians, support this conclusion.

Fishelson (1977) e x t e n d e d the ideas of M a c h r t h u r and W i l s o n (1967, Patrick (1967), and Slobodkln and Sanders (1969), about stability and instability of marine ecosystems to coral reefs. He d i f f e r e n t i a t e d b e t w e e n two phases in the d e v e l o p m e n t of the system: a) S u c c e s s i o n w h e n c o l o n i s a t l o n and c o m p e t i t i o n g r a d u a l l y proceed to a stable climax community in w h i c h the p r o b a b i l i t y of s u c c e s s f u l c o l o n i s a t i o n by a new species is m u c h lower than for c o l o n i s a t l o n by i n d i v i d u a l s of one of the species already occurring in the community. b) Speciation by invasion of as niches of an or less c o n s t a n t

is the s e c o n d stage when species e n r i c h m e n t by evolution occurs (as well as rare species); u s u a l l y extreme s p e c i a l i s t s utilise suitable m i c r o h a b l t a t s e x i s t i n g climax system. In this case, the specific c o m p o s i t i o n remains more and the c h a n g e s in species' seasonal a b u n d a n c e are predictable.

M a n - m a d e p e r t u r b a t i o n s (and e x t r e m e climatic events) d e s t a b i l i s e the climax system causing them to revert to a p r e - c l i m a x stage w h i c h may be d o m i n a t e d by opportunistic species and is more likely to be c o n t r o l l e d by a b i o t i c - p h y s i c a l parameters rather than by biological factors. In short, they d i s r u p t the p r e d i c t a b i l i t y of the ecosystem development. There are indications that s u c h p e r t u r b a t i o n s are b e g i n n i n g to influence the reef communities in the Gulf of Ai-Aqabah. B e n a y a h u and Loya (1977b) and M a s t a l l e r (1979) postulate that the c o n s p i c u o u s increase of h e r b i v o r o u s sea u r c h l n p o p u l a t i o n s in the northern Gulf could indicate radical p e r t u r b a t i o n s of the e c o s y s t e m b a l a n c e are occurring. The increase in abundance of D i a d e m s setosum, E c h i n o t h r i x d i a d e m s and T r i p n e u s t e s g r a t i l l a may disrupt the e q u i l i b r i u m of species c o m p o s i t i o n and s e t t l i n g density of the diverse benthic communities of the upper sublittoral. The p r o d u c t i v i t y of d i f f e r e n t soft and stony corals was m e a s u r e d at the L-I test site (Mergner and S v o b o d a 1977; S v o b o d a 1978) by in situ m o n i t o r i n g of oxygen production and respiration. During 24h in sltu m e a s u r e m e n t s , all species h a r b o u r i n g zooxanthellae showed a c o n s p i c u o u s surplus in 02 p r o d u c t i o n , down to a 40m depth. The m a x i m u m 02 c o n s u m p t i o n and p r o d u c t i v i t y per unit dry w e i g h t of coral tissue were found b e l o w 5m, p h o t o i n h l b l t i o n r e s u l t e d in a decrease of 25 to 50~ at im depth. 02 c o n s u m p t i o n during photosynthesis was 20 to 30g h i g h e r than during the night. T h e r e is a slight d e c r e a s e in 02 production after r e a c h i n g m o r n i n g light s a t u r a t i o n values; this m i g h t be caused by the storage of metabolic products. Xenllds show a gradual increase in o x y g e n output, caused by a diurnal rhythm of colony contraction.

c) Permanent chan~es: Small scale, gradual permanent changes in the coral assemblage were followed by M e r g n e r (1980, 1981) and M e r g n e r and S c h u h m a c h e r (1981) on the fore reef in an experimental area U-7, w h i c h was another 25m 2 quadrat. A cnidarian biocoenosis c o n s i s t i n g of 2046 colonies of 104 species was followed (Table i). There were 78 s c l e r a c t i n i a n species with 1274 colonies (50.95 cover) w h i c h included 34 of the 70 genera known from the Red Sea, and 19 a l c y o n a r i a n species (II genera) with 749 colonies (48.6~ cover). The unusually high

872

H. M e r g n e r

species dive~slty (H=3.67) and a b u n d a n c e in this reef region situated at the most northerly boundary of the global reef belt are a t t r i b u t e d to the r e l a t i v e l y conBtant c o n d i t i o n s o£ illumination, temperature and w a t e r movement in the m i d d l e fore reef. 0£ the species found the~e, about 505 were frequent at ]-Sm depth, 80~ in 5-15m and 40~ in 15-~Om.

T A B L E l.

C o l o n i s a t i o n by Cnidaria in the test area U-7 fore reef of the fringing reef south of Aqaba.

Non - C n i d a r i a Ca (ofalhnaceae Po~ Por,t'era Cnidaria Hydrozoa 1 Millepota exaesa A n t h o z o a - Octocoraltia Tubiporidae Z Ttbipora musics Alcyoniidae

Podfloporidae 23 5etiat~oora ~aliendforn 24 Se,iatopora sp. 25 $/ylopho~ pislillafa Acroporidae Z6 Ac[opo[a c/avi~era 27 Attopota euryMoma 28 Actopora fo/s~afi 29 Acropora hemptichi

CladielLapachycl~do5 4 Lobophytum 5p. 5 Paretyfhropodium futvum 5arcophy/on ehrenbergi 7 Sinulatia lep/oclados 8 5inulafia sp. Nephfheida 9 Dendfonephfhya sp lO Nephfhea ,~lbida 11 Lilhophylon arboreum 12 Paralemnalia fhyrsoides Xeniidae 13 HeleroxenM [u~cescens 14 XenJa macrospitutafa 15" Xenia mernbranacea 16 Xeni.t obscufonala

30 Acfopora humili5 ~1 Acropota 5candens 32 Acropora sfuarposa 33 Acropora variabilis 34 Actopora sp. 35 As#eopo~ myriophfha/ma 36 Monfipora dense 37 Montipora effuse 38 Aaonlipora eil~fensi5 39 Montiporw meandrina 40 Monlipora monas#ermfa 41 ~ontipma sfilose 42 Montipma venosa 43 Monlipora sp. Agariciida e 44 6ardineromens penderos~ 45 Lepfosa¢i$ jp.

46 Pachyseris speciosa 47 Pavone dense 48 p#vona clecussafa 4g P,~vona var;ans

17 Xenia spat. 18 Xenia umbellate

Siderasffeidae

A n t h o z o a - Hexacorallia

So Coscinarea monile

Faviidae 61 Caulastrea tumida 62 Cyphastreachalcidicum G3 Cyphaslre~ mitrophlhatma 64 Cyphasfre~ se[ailis 65 Cyph,l~frea sp. 66 Ed~inopora gemmacea 67 [chinopor~gdrmmaceafreticeio~a 68 Echinoporalemellosa 69 Favia amicerum 70 Favia fare5 71 Favia laxa 72 [avis p#llida 73 Favia sfelligera '/'4 Fav/a sp. 75 Favlfes abdifa 76 Favifes peresi 77 FavJfes sp. 78 GOniastre~ edwardsi '79 Goniasfrea pecflnafa 80 Gonimsffea [efiformis 81 Goniaslrea sp. 82 /tydnophora exesa 85 Lepfaslrea bo/fae 84 Lepfa#rea purpurea 85 Lepta=free fransversa 86 Monfas#tea forskaelana 87 Plah/gyta lameflin,7 Oculinidae 88 Galaxea fescl'cularis

/Herulinidae 89 Meruhna ampfia~a

Fungiidae

Actiniidae G.h. Gyros/ores hehanfhus Gq. Gy~ostoma quadricolor R.k. R~dianthu5 ko$e~ren~is Thamn~sferiidae lg Psammocora superficiali~ Pocilloporidae 20 Pocillopora damicornis 21 Poc#lopo[a danes 22 ~etiafopora angulafa

Sl Cydoseri$ doederleim 52 CvcloserJ~ Sp.

5~ Fungia fungitss ~ FungUs grmnulo~a Pod~ides 5~ A!veopora dRed~lea ~ Goniop~-a planulafa 57 Goniopo~a sW ~8 Porife~ (5ynarea) convexa 59 Potifes lures 60 porlfes sp.

Substrata :

~

(oral rock

~

Mussidae 90 Acanlhaslrea echinala 91 Zobophyl/ia corymbosa 92 Zobophyllia co=tale 93 Lobophyl/ia hempr~chi Pecfiniidae 94 Echlnophy/lie aspera 95 Mycedium tubifex Dendrophyiliidae 9~ Tutbina~ia me~enferina Zoanfhidae 97 patylho~ ~ubercuiosa sand

C o l o n i z a t i o n b y C n i d a r i a in the t e s t area U-7 ,Core reef" Of the fringin 9 r e e f soufh of Aqaba

Coral

Reefs

of the Red Sea

873

,~r

~¢or,~l

rock

Fig.8.

~

$and

~

~liv~ coral colonies

m

V

4

cora/ colonies dead after 2o monfhs

~ I

coral colonies I overgrown by algae

Map of the test a r e a U-7 in the fore reef 6km south of Aqaba h a r b o u r showing the spatial s t r u c t u r e of the coral community and the changes w h i c h o c c u r r e d b e t w e e n F e b r u a r y 1976 and S e p t e m b e r 1977. A list of the coral s p e c i e s is g i v e n in T a b l e 1 (after Mergner & Schuhmacher, 1981).

sm

874

H. Mergner

In this r e g i o n cnidarian a s s e m b l a g e s were a f f e c t e d by grazing sea urchins (especially by D l a d e m a setosum) and parrot fishes, by o v e r g r o w t h of xenlids and by sedimentation. Grazing, c o m p e t i t i o n for space and s e d i m e n t a t i o n create a m o s a i c pattern of v a r i a t i o n in species abundance and v a r i e t y w i t h i n the coral community. Partial m o r t a l i t y can result in the breakup of a big colony into many smaller units which may be counted as distinct colonies, thus influenclng the o b s e r v e d diversity index, but in no other reef a r e a of 5x5m have such extreme hlgh values for abundance and diversity of corals been observed. M e r g n e r and S c h u h m a c h e r (1981) r e p o r t e d the changes that occurred w i t h i n this climax community d u r i n g only 20 m o n t h s (Fig.8), involved settlement by innumerable very small colonies, and the d e a t h of 27 a l c y O n a r l a n (0.69% coverage) and 53 s c l e r a c t i n i a n c o l o n i e s (1.54% coverage). Each species was affected differently, and all these changes occurred within a climax community. However, these o b s e r v a t i o n s do n o t c o n t r a d i c t t h e i d e a s o f F t s h e l s o n (1977) c o n c e r n -

ing the development o f e c o s y s t e m s . Community s t r u c t u r e i s dynamic d e s p i t e t h e e c o l o g i c a l equilibrium and the e v o l u t i o n a r y s t a b l e e n v i r o n m e n t . Ftnatly, compared w i t h L o y a ' s (1972) data from Ellat on the o p p o s i t e side of the Gulf, these a b u n d a n c e and d i v e r s i t y data differ remarkably; the species and colony number of the middle fore r e e f south of A i - A q a b a h was c o n s i d e r a b l y higher than those of the c o m p a r a b l e zone of the Ellat reef. The species diversity (H) in the middle fore reef of Ellat was 2.67 c o m p a r e d with the values for A i - A q a b a h of 3.67 based on the colony number and 3.42 based on that of settlement area. These d i f f e r e n c e s may either r e s u l t from the g r e a t e r precision of one of the methods, or the a r b i t r a r y selection of the study area within the m i d d l e fore reef. Nastaller

(1979)

also

used q u a d r a t e o f d i f f e r e n t

sizes

to

study

t h e c o m p o s i t i o n and e c o l o g y

of mollusc and echinoderm populations on t h e c o r a l r e e f s of A1-Aqabah. Collections revealed the presence of 531 m o l l u s c a n species (Including 248 new records for the G u l f and 96 for the Red Sea) and 83 e c h i n o d e r m species (including 28 new records for t h e Gulf and 3 for the Red Sea). The e n v i r o n m e n t a l conditions of the m l c r o h a b l t a t s w h i c h these species inhabited were determined. Altogether, ii reef zones were investigated. Autoecologlcal experiments and a n a l y s e s of some of the animal p o p u l a t i o n s showed their p r e f e r e n c e s and s t r a t e g i e s , and s y n e c o l o g i c a l c o m p a r i s o n s of certain b i o c o e n o s e s and thelr m l c r o h a b l t a t s r e s u l t e d In a better u n d e r s t a n d i n g of the r e l a t i o n s h i p between substrate type and s e t t l e m e n t structure. Finally, s t o m a c h c o n t e n t s of the important m o l l u s c s and e c h i n o d e r m s w e r e a n a l y s e d and the feeding a c t i v i t i e s of four of the s e a - u r c h i n species were observed. The most active species, T r l P n e u B C e s E r a t i l l a c a u s e d the heaviest d i s t u r b a n c e to the coral r e e f ecosystem. Similarly, Nobbe ( p e r s o n a l c o m m u n i c a t i o n ) has l n v e s t t j ~ a t e d t h e e c o l o g y and s p e c i e s c o m p o s i t i o n o f t h e

sponges occtuerlng on t h e r e e f

u s i n g both q u a d r a t s and t r a n s e c t s .

Competition i n S , e t j t ! e , c o m m u n t ~ ! e s The role of c o m p e t i t i o n for space and light b e t w e e n sessile a n i m a l s on Red Sea coral reefs will now be discussed. Studies s p e c ! f l c a l l y d e v o t e d to this p r o b l e m are few, but it is discussed i n some of the more general ecologlcal papers based, for example, on reef zonatlon, Flshelson (1970) in his s t u d i e s of n o n - s c l e r a c t l n l a n a n t h o z o a n s of the s h a l l o w w a t e r reefs of Ellat and Sinai, p r o v i d e d some i n f o r m a t i o n on the s u b s t r a t e - d e p e n d e , t d i s t r i b u t i o n s and the habitats o f 22 s p e c i e s o f sea anemones and 20 s p e c i e s o f a l c y o n a r i a n s , and d e s c r i b e d how e x t e n d e d a r e a s o c c u r c o v e r e d by x e n l l d s such as X e n l a . . ~ l ~ t a and H e t e r o x a a i a f u s c e s c e n s , and by S ~ g p h y t o n eba'enbcrgi and o t h e r s , o v e r g r o w i n g dead C o r a l r o c k , o r f ~ u e w o r k s o f dead c o r a l bushes l i k e those o f S e r t a t o p o r a . He c o n c l u d e d t h a t e x t e n s i v e s u b , a c e c o v e r a g e by a l c y o n a r t a n s and sea anemones can p r e v e n t t h e r e s e t t l e m e n t and d e ve lo p m e n t o f young h e r m a t y p ! c coral colonies. The role of soft corals as c o m p e t i t o r s to h e r m a t y p i c corals in b i o c o e n o s e s of the Ai-Aqabah reefs was also d i s c u s s e d by S c h u h m a c h e r (1975), M e r g n e r (1981) and Mergner and S c h u h m a c h e r (1981). C o m p e t i t i o n for light is the decisive factor in the c o l o n i s a t l o n of pilings in the m e r c h a n t h a r b o u r of Eilat by sessile animals and algae (Schuhmacher, 1973a). Four settlement zones were d i s t i n g u i s h e d : a bright zone (where irradiance was 13-3~ of the surface intensity) in w h i c h T F i d a c n @ maxima, T. s q u a m o s a and P a d l n a p a v 0 n i c a were indicator species; a diml i g h t zone ( w i t h 3-1% s u r f a c e i r r a d i a n c e ) , w i t h S l p h o n o c h a l l n a s ! p h o n e l l a and DegdronephthYa; a very d i m - l i g h t zone (with 1-0.4% surface irradlance) with A c a b a r t a b l s e r l a l l s and C l a t h r a r l a rubrlnodis; and a dark zone (with 0 . 4 - 0 . 1 % surface irradiance) w i t h violet L i t h o t h a m n i o n and L l t h o p h ~ l l u m . The animal zonation r e l a t i v e to the horizontal light gradient was s]mi]ar to that o c c u r r i n g v e r t i c a l l y on the reefs. Illumination is the d o m i n a n t environmenta~ f~ctor. which affects the d i s t r i b u t i o n s of the majority of species inhabiting the reefs

Coral

Reefs

of

the

Red S e a

875

Interspecific competition i s a l s o an i m p o r t a n t factor influencing settlement, even during the initial phases of reef development. It is rarely possible to follow the initial stages of coral reef formation, but Schuhmacher (1974, 1977) observed tile succession in settlement of reef species on c o n c r e t e blocks emplaced as breakwaters at the barbour at Eilat. Initially there was a r a p i d and homoger~us colonisation by f o u l i n g organisms. The initial eolonisers were grazed down by s e a - u r c h i n s and r e p l a c e d by m o l l u s c s , calcareous red algae and foraminiferans which were unaffected by t h e g r a z i n g animals. Pioneer frame-building seleractinians and hydrocorals then settled particularly on t h e r e m a i n s o f r o c k - a t t a c h e d shells, and secondary frame-builders developed in their shelter. Encrusting calcareous algae, foraminiferans and bryozoans then began c o n s o l i d a t i n g the c o r a l l i n e framework. The m a t r i x of l i v i n g c o r a l s was then i n h a b i t e d not only by decapods and m o l l u s c s , but a l s o by boring organisms like Lithophaga. The activities of the borers facilitated invasion by Cliona spp. Thus bioerosion begins at a very early stage in reef development.

Loya (1976c) studied settlement, mortality and recruitment of a population of Stylophora pistillata on artificial objects emplaced in front of the Marine Laboratory at Eilat over a period of 33 months, during which mortality rates within the population varied between 70 and 95%. Mergner (1979) found similar mortality rates occurring in the reef lagoon Li area near A1-Aqabah and found that only 10% of the young colonies survived up to one year. According to Loya, the youngest colonies suffered the heaviest mortality, mostly caused either by strong southerly storms, or by predation by parrot fishes, wrasses, trigger fishes, Quoyula monodonta, Lithophaga lessepsiana, Cliona and Diadema setosum. Stylophora is a pioneer coral which heavily colonises unexploited habitats. An average number of 60 new colonies per m 2 settled on substrates during the peak of the reproductive period. However, in the stable climax community of the lagoon area L-I on the AI-Aqabah reefs, the settlement rate by young colonies was much less because of competition from the rapid growth of algae which settled simultaneously (Mergner, 1979). In the area of the Eilat reefs, studied by Loya (19?6a,b,c) St~lophora pistillata was the major coral contributor to the reef framework. It is an "r strategist" (r refers to the maximal intrinsic rate of natural increase, rm, (MacArthur and Wilson, 1967 ). Loya (1976a) adapted the summary by Pianka (1970) of the characteristics of such a strategist to St~lophora success in colonising unpredictable reef habitats, rapid development, great population turnover, early reproduction, high intrinsic rate of natural increase, small body size, short life span, density-independent mortality, wide dispersal gradient and poor competitive abilit~ -

Loya (1976a) considered the reef flat at Eilat to provide a relatively unpredictable environment because of periodical occurrence of extremely low tides. Stylophora diverts a substantial proportion of its available resources into reproduction during 8 months from December to July. Small colonies with a diameter of only 4-5cm and an age of only 2-3 years already contain ripe eggs and can release more than i00 planulae each evening. An important feature of St~lophora pistillata is its pioneering ability to colonise new environments and unexploited habitats (Loya, 1976c), for example, a newly installed seawater supply pipe at the Marine Laboratory at Eilat was rapidly colonised. Its initial growth rate and the rate of its regeneration of broken branches are among the fastest known for the scleractlnian species of the Gulf of A1-Aqabah. It occurs over the full depth range of the reef, but when subjected to competition for space, Stylophora is the first excluded by deep reef specialists. Thus although S. plstillata is such an effective pioneer, it ranks among the lowest in the aggressive hierarchy. Rinkevitch and Loya (1983a,b) found that in intraspecifie competitive interactions between the two colour morphs of Stylophora pistillata, purple colonies competitively excluded the yellow morphs, even in the absence of any physical contact, but larger colonies were competitively superior over smaller ones. The outcome of those interactions is the synergistic effect of different aggressive responses, such a s nematocyst discharge, overgrowth and retreat growth which results in gaps of 30~m forming around the edges of branches. Apparently no physical contact is required for branches of a colony to identify their common identity. Stylophora-colonies were grafted with alien branches labelled with 14C, which demonstrated the translocation of photosynthetic metabolites from the grafts into the host tissue which then uses them for its own metabolic requirements. The highest concentrations of the translocated material accumulated in the tips of the host branches, far away from the contact zones. Aspects of competition in other reef-dwellers were studied by Magnus (1960) and Niggemann (1968 who worked on populations of Ocypode and Coenobita respectively; by Mergner (1967, 1977) and Mergner and Wedler (1977) working on hydroids; by Mastaller (1978) on molluscan

876

H. M e r g n e r

a s s e m b l a g e s o f P o r t Sudan; by S h e p p a r d ( 1 9 8 2 ) on c o r a l p o p u l a t i o n s ; by V i n e ( 1 9 8 4 ) on t h e e f f e c t s o f a l g a l g r a z i n g and a g g r e s s i v e b e h a v t o u r o f S t e g a s t e s n , ! s r i c a n s and A c a n t h u r u s s o h a l ; and by o t h e r s .

Influence of Pollution and Low Tides Most natural and anthropogenlc substances influence the reefs and their biocoenoses in the northern Gulf of AI-Aqabah. In many other parts of the Red Sea disturbance by man and severe damage by natural catastrophes have been increasingly reported. D i s t u r b a n c ~ b y man include pollutlon by o11 spills, fertlllsers, industrial waste water and sewage, heated effluents of desalination plants, exploslves for fisheries, buildlng activity along the sea-shore and collection of rare specimens for sale to tourists. Natural catastrophes include strong stormsi infrequent torrential raln storms but in particular extremely low equinoctial tides if they coincide with cold north winds or hours of fierce sunlight. Nergner (1981) has summarlsed all the data on the effects of these catastrophes, comparing studies in the Gulf of AlAqabah on the Sinai side (Flshelson 1973a,b; Loya 1975, 1976d; Loya and Rinkevlch 1979, 1980) and on the Jordan side (Walker and Ormond, 1982) with his own data. Pollution in the Red Sea is discussed by other contributions to this symposium by Bebehani and Fowler and his colleagues, so here only the ecologlcal consequences of such perturbations, and the recovery of the reefs will be discussed. Flshelson (1973a) studied the effects of pollution on the reef flat at Eilat, by using the transect technique. From 1966-1972 he observed that the number of living coral colonies decreased along 190m of transect from 541 to only 195. This decrease in numbers of coral was accompanied by an increase in algal growth over the coral. Branchlng mlcropolypal coral species like Acropora, P o c ! l l o p o r a , Serlatopora and Stylophora were especially sensitive to algal cover: only i0 out of 192 colonles survived within the 6 year period. Flshelson conslde~ed this high mortality to be caused by frequent oil spills together with eutrophication caused by phosphate dust stimulating the growth of algae.

Simultaneously in 1970, an exceptionally low tlde occurred which resulted in the death or damage of many coral colonies at the reef flat of Eilat. Fishelson (1973b) marked these colonies and monitored each month over the following two and a half years to follow thelr regeneration and the algal growth on the exposed skeletal surfaces. Once agaln it was the bushy micropolypal species which proved to be much more sensitive to desiccation than the braln-shaped macropolypal species, such as F a ~ a , Gop~&sSF~s and ~ . Regeneration began from su~vtving tissue but developed differently In the m $ c r o p o l y p a l and mac~opolypai forms. Principally, t h e n e o b l a s t b e c o m e s e n r i c h e d w i t h z o o x a n t h e l l a e and a d v a n c e s , d e p o s i t i n g a new c a l c i u m c a r b o n a t e l a y e r o v e r t h e o l d s k e l e t o n . Unpredictable e x t r e m e - l o w tides may limit the abundance of corals on the reef flat and so reduce competition and preserve the h i g h species diversity. However, if they occur too frequently, they will seriously endanger the reef community, especially if combined synergistiCally with human and other natural perturbations (Pearson, 1981). Single, even quite serious disturbances can be tolerated so long ss there Is sufficient time before the next major catastrophe for the ecological equilibrium to he re-established (Fishelson, 1977). Loya (1975) came to similar conclusions when he compared the effects of chronic oil pollution on the reef flat at the nature reserve at Ellat with that on a control reef 5km south. He found that the repeated oil spills damaged the corals in several ways. In addition t o the damage caused by the toxic compounds, the oil fllm can seriously limit oxygen exchange, and photosynthesis by its shading effect. The alteration of the physical properties of the reef surface by the oll inhibits the settlement of larvae and therefore the recolonisation of the reef. In addition, laboratory experiments on the toxic effects of crude-oil on scleractinian species (Loya and Rinkevlch, I979, 1980) have shown in Stylophora p ~ ! l l a t a that not only is damage inflicted on the reproduction system but also the settling of its larvae is prevented. Loya (1976d) in studying the consequences of the catastrophic low tide of 1970, compared the recovery of the scleractinlans on the chronically polluted reef flat at Eilat with a pollutlon-free control reef 3Okm south (Table 2).

Coral

Table

2.

Reefs

of the Red Sea

877

S u m m a r y of the r e l a t i v e changes in the total number of coral species and c o l o n i e s r e c o r d e d at the chronically polluted nature r e s e r v e (21 transects) and the control reef (12 transects) d u r i n g ].969-1973 (from |Joys (]976d}, Table ~i P- 285)

I].I%[IPe reserve Total

number

of s p e c i e s

in 1969

!~2

~3

Total

number

of species

in 1973

23

39

0

]o

Number

of new species

Number

of e x t i n c t

Percentage

i.

centre]

recorded

species

increase

19

4 18.2

1973

-45.2

Total

number

of c o l o n i e s

in 1969

842

416

Total

number

of c o l o n i e s

in 1970 after

128

80

85

81

-80

40

Percentage

mortality

Percentage

increase

till

in ]973

in 1973

after till

low tide

low tide

1970

1973

Percentage

of r e g e n e r a t i o n

Percentage

of r e c o l o n i s a t i o n

in 1973 in 1973

reef

77

13.6

23

86.3

Extent

of r e c o l o n l s a t l o n I

1.8

42 . l

Extent

of r e g e n e r a t l o n 2

6.4

6.6

i.e.

the a v e r a g e

number

of c o l o n i e s

per transect

resulting

2. i.e.

the a v e r a g e

number

of c o l o n i e s

per t r a n s e c t

originating

from larval

settlement.

from survivors.

The coral c o m m u n i t y s t r u c t u r e and s p e c i e s d i v e r s i t y of both reefs were used to compare the m o r t a l i t y rates f o l l o w i n g the e x t r e m e l y low tide and the extent of the subsequent r e c o v e r y o v e r the next 3 years. Both reefs s u f f e r e d m a s s m o r t a l i t i e s of the corals (85~ at the nature reserve at Eilat a n d 81% at the c o n t r o l reef), but a significant d i f f e r e n c e was o b s e r v e d in their r e c o v e r y : coral r e c o l o n l s a t i o n at the control reef was fast and over 20-fold g r e a t e r than at the p o l l u t e d r e e f where colony number, species number, coverage and d i v e r s i t y w e r e still d r a s t i c a l l y d e c r e a s e d 3 years later. The most common species on the control reef in 1969 s h o w e d the h i g h e s t rates of r e c r u i t m e n t in 1973, which might indicate the o p p o r t u n istic b e h a v i o u r of these species. H o w e v e r , in 1973 the diversity on the control r e e f was h i g h e r than in 1969, and L o y a (1976d) i n t e r p r e t e d this as confirming that after a p e r t u r b a t i o n d i v e r s i t y t e m p o r a r i l y i n c r e a s e s until space b e c o m e s limiting, when interspecific c o m p e t i t i v e i n t e r a c t i o n s cause d i v e r s i t y to d e c l i n e again. L o y a c o n c l u d e d that whereas a h u m a n - p e r t u r b e d e n v i r o n m e n t m a y not r e t u r n to its former structure, reef areas d e n u d e d by natural d i s t u r b a n c e s are m o r e l i k e l y to r e v e r t to their p r e v i o u s structure. Finally, periodic d i s t u r b a n c e s by n a t u r a l p h e n o m e n a such as e x t r e m e l y low tides prevent the r e e f flat b e c o m i n g d o m i n a t e d by a l i m i t e d n u m b e r of d o m i n a n t species, and so provide an important d i v e r s i f y i n g force. L o y a (1976b) m a d e f i e l d o b s e r v a t i o n s on s k e l e t a l r e g e n e r a t i o n in a population of the stony coral S t y l o p h o r a p l s t i l l a t a at Eilat. He m a r k e d 70 colonies before b r e a k i n g some of their b r a n c h e s , a n d then a n a l y s e d their r e g e n e r a t i o n . The previous growth rate d a t a from a p p r o x i m ately 200 u n d a m a g e d c o l o n i e s were u s e d as controls. Initially, r e g e n e r a t i o n began by living tissue O V e r the a r e a of the break w h i c h p r e v e n t e d the settlement of fouling organisms. Alt h o u g h the g r o w t h r a t e of s m a l l e r c o l o n i e s w a s higher, the bigger colonies had a g r e a t e r c a p a c i t y to r e s i s t the i n v a s i o n by f i l a m e n t o u s algae and other settlers which could o t h e r w i s e prove fatal to the colonies. In all, 19 of the e x p e r i m e n t a l l y d a m a g e d colonies died. There are few data from the Jordan side of the Gulf. Mergner (1981) reported on two o i l spills in fall 1975 and spring 1976, and W a l k e r and Ormond (1982) studied the effects of phosphate pollution. B o t h oil slicks o b s e r v e d by Mergner (1981) polluted the eulittoral zone of the f r i n g i n g reef s o u t h of the U n i v e r s i t y Bight. Immediately after the p o l l u t i o n no settlers s u r v i v e d there, but 4 m o n t h s later the T e t r a c l i t a squamosa and E n t e r o m o r p h a zones showed

878

H. M e r g n e r

recovery and r e c o l o n i s a t l o n by T e t r a c l l t a was occurring. Only in the sandy substrates the u p p e r eulittoral w e r e p a t c h e s of oily r e s i d u e s still i n h i b i t i n g recovery, notably the anomursn H i p p a p i c t a w h i c h n o r m a l l y inhabits the d e e p e r layers of the sand.

of of

Damage to the coral c o m m u n i t i e s caused by e x t r e m e - l o w tides and effects of e u t r o p h i c a t i o n have also been r e p o r t e d from the E g y p t i a n coast of the Red Sea near Al-Qusayr. In ~977, M e r g n e r (1981) r e p e a t e d K l u n z i n g e r ' s (1872) o b s e r v a t i o n s at the reef flat and fringing reef south of AI-Qusayr and found clear e v i d e n c e of e u t r o p h i c a t i o n leadlng to extensive algal growth. The reef flat was totaIly o v e r g r o w n by algae, one kilometre d o w n - w i n d of a phosphate factory from which an extensive plume of p h o s p h a t e - d u s t was being blown by the prevailing northerly winds.

FUTURE R E Q U I R E M E N T S FOB E C O L O G I C A L RESEARCH ON RED SEA C O R A L REEFS The future existence of the r e e f s needs serious c o n s i d e r a t i o n . In an e n c l o s e d and narrow coral sea llke the Red Sea, the e f f e c t s of both noxious h u m a n influences and natural catastrophes are more tangible than in open oceans, hence these reefs may serve as important sites fop assessing origin and effects of c a t a s t r o p h i c changes w h i c h e l s e w h e r e may only be recognlsed after months or years. Already, the a p p a r e n t l y u n r e s t r a i n e d algal growth and conspicuous increase of h e r b i v o r o u s e c h i n o i d p o p u l a t i o n s in coral reefs of the Gulf of AI-Aqabah and other regions of the Red Sea indicate serious d i s t u r b a n c e s to their previously stable equilibrium. The c o n t i n u i n g increase in pollution r e q u i r e s careful m o n i t o r i n g to detect as early as possible the first i n d i c a t i o n s of d e t e r i o r a t i o n . For example, an immediate start must he made on f o l l o w i n g the e n v i r o n m e n t a l impact of d e s a l i n a t i o n plants, r e f i n e r i e s , loading facilities, coastal industrial plant, m a r i n e t r a n s p o r t a t i o n of oli and phosphate, fisheries, and the increasing pressure from tourism. Baseline studies are u r g e n t l y needed of pristine reefs, so that when adverse changes are d e t e c t e d or s u s p e c t e d p r o p e r l y d e s i g n e d r e s e a r c h programmes can be immediately i n i t i a t e d to assess the extent of the impact. Reef c o m m u n i t i e s are capable of extensive r e g e n e r a t i o n and r e c o l o n l s a t i o n after damage if not s i m u l t a n e o u s l y exposed to further perturbatlons. W i t h o u t careful r e s o u r c e m a n a g e m e n t b a s e d on sound ecological investigations, the climax c o m m u n i t i e s of the Red S e a ape t h r e a t e n e d by severe and possibly irr e v e r s i b l e changes s i m i l a r to those met w h i c h have o c c u r r e d in the M e d i t e r r a n e a n and other localities. Strict protection and c o n s e r v a t i o n of t h e Red Sea coral reefs a r e of o v e r r i d i n g importance. T h i s c a n o n l y be a c h i e v e d if there is f u l l s c i e n t i f i c cooperation between all nations borderi n g t h e Red S e a i n o r d e r to coordinate reef conservation, rationally manage fisheries and tourism, and to take e f f e c t i v e legal and e n v i r o n m e n t a l a c t i o n to counter severe pollution. The success of such m e a s u r e s can only be assured if they are s u p p o r t e d by extensive and thorough ecological research. Ecological studies on Red Sea r e e f s should c o n c e n t r a t e on the following: i. More d e t a i l e d k n o w l e d g e is n e e d e d on the p o p u l a t i o n d y n a m i c s of the different reef b l o c o e n o s e s and b i o p h y S i o g r a p h l c zones. Q u a n t i t a t i v e a n a l y s e s of seasonal and longterm changes are n e e d e d as a basis for the m o n i t o r i n g of the i n f l u e n c e s of m a n ' m a d e perturbations and natural c a t a s t r o p h e s , and is best done by r e p e a t e d a n a l y s i s of fixed quadrats. 2. S y n e c o l o g i c a l studies are needed for the u n d e r s t a n d i n g of i n t e r s p e c i f i c competition for space, light and food b e t w e e n members of the r e e f community, and the adaptive features shown by individuals and species to the reef habitat. 3. A u t e c o l o g i c a l studies of s i n g l e animal species and groups; some of these such as sponges, molluscs, e c h i n o d e r m s and fishes, have r e c e i v e d some attention, but almost nothing is known about other taxa like flatworms, ribbon worms, crayfish, polychaet4s, slpunculids, h e m l e h o r d a t e s and asoidlans. 4. The cryptic fauna of the Red Sea coral reefs is poorly known ecologlcally. This fauna inhabits holes and crevices in the coral rock, under broken rock and the inside of rubble screes, where it forms a series of m i n i a t u r e biocoenoses. I n v e s t i g a t i o n s of the cryptic f a u n a need to overcome the problems of inadequate taxonomy and major difficulti~ in m e a s u r i n g their living c o n d i t i o n s in the field or by laboratory experiments.

Coral Heels of the R e d Sea

879

ACKNOWLEDGEMENTS Grateful acknowledgements are due to Deutsche Forschungsgemelnschaft for financial help, to all colleagues workin K with me on ~ed Sea coral reefs, and to the co-workers Of my institute for help in preparing this manuscript and its illustrations, and to Dr. M.V. Angel for carefully correcting and editing it.

REFERENCES Abel, E.F. ( 1 9 6 0 ) . Zur K e n n t n i s des V e r h a l t e n s und der Okologie yon F i s c h e n an K o r a l l e n r i f f e n b e i Ghardaqa (Rotes Meet). Z e i t s c h r i f t f u r Morphologie und Okologie der Tiere~ 49, q30503. Bamber, R.C. ( 1 9 1 5 ) . R e p o r t s on t h e marine b i o l o g y o f Sudanese Red Sea. XXII - The F i s h e s . J o u r n a l o f t h e Linnean S o c i e t y , London, 31, ( 2 1 0 ) , 477-485. Baschieri-Salvadori, F. (1954). Spedizione subacquea Italiana nel Mar Rosso. Ricerche Zoologiche VII - Chetodontldae. Rivista di Biologla Coloniale, Rome, lq, 87-110. Benayahu, Y. and Y. Loya (1977a). Space partitioning by stony corals, soft corals and benthic algae on the coral reefs of the northern Gulf of Eilat (Red Sea). Helgol~nder wissenschaftllche Meeresuntersuchungen, 30, (I-4), 362-382. Benayahu, Y. and Y. Loya (1977b). Seasonal occurrence of benthic algae communities and grazing regulation by sea urchins at the coral reefs of Eilat, Red Sea. Proceedings of the Third International Coral Reef Symposium I Miami, 383-389. Ben Tuvla, A. (1963). Fisheries investigation of the Israel south Red Sea Expedition. Fishermen's Bulletln, Haifa, 32, 3-26. Ben Tuvia, A. and H. Steinitz (1952). Report on a collection of fishes from Elyath, Gulf of Aqaba, Red Sea. Bulletin of Sea Fisheries Research Station, Halfa, (2), 1-12. Chamisso, A.v. and K.W. Eysenhardt (1821). De animallbus quibusdam e classe vermlum Linneana, in circumnavlgatione terrae, auspicante Comlte N. Romanzoff, duce Ottone de Kotzebue, annis 1815-1818 peracta, observatis. Nova Acta Physico-Medica Academia Caesarea Leopoldino Carolinae Germanicum Natural Curiosorum~ I0, 343-374, pls. 24-33. Clark, A.M. (1952). The 'MANIHINE' Expedition of the Gulf of Aqaba 1948-1949. VII. Echinodermata. Bulletin of the British Museum (Natural History)~ Zoology, I, 203-214. Clark, A.M. and F.W.E. Rowe (1971). Monograph of Shallow-Water Indo-West Pacific Echinoderms. Trustees of the British Museum (Natural History), London. 238 pp. 31 pl. Cousteau, ff.Y. (1964). At home in the Sea. National Geographic Magazine, Washington, 465507.

Cousteau, ff.Y., W. Nesteroff and M. Tazieff (1953). Coupes transversules de la Met Rouge. XIXth International Geological Congress t Algeria, 1952, Fasc. I ~ topographie sous-marlne et sedimentation actuelle, 75-77. Crossland, C. (1907). Reports on the marine biology of the Sudanese Bed Sea. IV. The recent history of the coral reefs of the mld-west ~hores of the Red Sea. Journal of the Linnean Society, London, 31, 14-30. Crossland, C. (1911). Reports on the marine biology of the Sudanese Red Sea. XVIII. A physical description of IChor Dongonab, Red Sea. Journal of the Linnean Society, London I 31, 265-286, pls. 28-3q. Crossland, C. (1913). Desert and water gardens of the Bed Sea. Cambridge, 158 pp., 40 pls. Crossland, C. (1935). Coral Faunas of the Red Sea and Tahiti. Proceedings of the Zoological Society, London, 105, 499-504. Crossland, C. (1938). The Coral Reefs at Ghardaqa, Red Sea. Proceedings of the Zoological Society, London, 108, 513-523. Crossland, C. (1939). Some coral formations. Reports o n the preliminary expedition for the exploration of the Red Sea in the R.R.S. 'MABAHITH' (December 1934 - February 1935), Chapter III. Publications of the Marine Biological Station, Ghardaqa, Red Seat i, 21-35. Cuvier, G. and A. Valenciennes (1828-1849). Histoire naturelle des Poissons. Paris, 22 volumes. Dietrich, G., G. K~ause, E. Seibold, and K. Vollbrecht (1966). Relsebericht der Indischen Ozean Expedition mit dem Forschungsschiff 'METEOR' 1964-1965. 'METEOR' Forschungsergebnisse, Reihe A, No.l, 1-52. Dollfus, R.P. (1938). Stomatopoda (If). Catalogue synonymique des esp~ces Juskua present r6colt6es dans la Met Rouge, y compris la pal'tle sud du Canal de Suez et le Golf d'Aden. Mission Robert Ph. Dollfus en Egypte. M~moires de l'Institut d'Egypte, 37, 185-236. Dollfus, R.P. (1967). Au sujet du Laeops du Golfe de Suez. Bulletin du Museum d'Histoire naturelle, Paris, 39, (5), 843-845. Dunker, D. (1940). Uber einige Syngnathidae aus dem Roten Meet. Publications of the Marine Biological Station, Ghardaqa, Red Sea, 3, 83-88.

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