Community structure and diversity of reef-building

Coral reefs

99

Community structure and diversity of reef-building corals at Sharm EI-Sheikh, Red Sea, Egypt by Sayed A. K. Abo-Hegab, Wafai Z. A. Mikhail and Mohammed S. A. Ammar

Abstract: The distribution of reef build ing coral s was studied at Ras Umm Seid, Sharm EIShe ikh. Massive corals were found to be more abundant than other growth fonns . A total of 53 species was recorded. These species have been divided into 5 categories which are: 1- species widely distributed from the reef flat to the lower part of the reef slope. 2- species restricted to the reef flat and the reefs lope up to 10 m depth. 3- species restricted to the rcefs lope only up to 5 or 10 m depth. 4- species restricted to the reef slope only from 1-30 m depth . 5- species restricted to the deeper areas of the reef slope only. The colony size of reef-building species is always lower on the back reef than on the reef slope. The dive rsity indices as well as the number of species are high at the reef slope and decrease with increasing depth. The lowest values were recorded at the 25 -30 m depth zone. Kurzfassung: Die Verte il ung riftbil dender Korall en wurde am Ras Umm Se id in Sharm ElSheikh am Roten Meer untersucht. Es zeigte sich , daB massive Korall en h~ufi ger waren als andere Wuchsformen. lnsgesamt wurden 53 Arten festgestellt, die in drei Gruppen unterteilt werden k5nnen: 1- weitverbreitete Arten, deren Vorkommen sich von Flachriffbis in die unteren Bereich des Riffsaums erstreckt. 2- Arten, de ren Vorkommen vom Flachriff bis in 10 m Tiefe reicht. 3- Arten, die nur zwischen 5 und 10 m Tiefe am Riffsaum vorkommen. 4- Arten, die zwischen 1-30 m am Riffsaum vorkommen, und 5- Arten . die nur im Tiefenberei ch des Riffsaums vorkommen. Die KoloniegrOfie der Korallen ist auf der ROckseite des Riffs ste15 geringer als am Riffsaum. Der Artenindex und die Anzahl der Arten sind am Riffsaum groB, nehmen aber mit zuneh mender Tiefe abo Die geri ngsten Werte werden in einer Tiefe von 25- 30 m erreicht. Key words: coral reefs, Red Sea, ordination, species diversity, marine ecology.

Introduction The zonation of the commu nities on the outer slope of coral reefs is defined as a result of the decrease of hydrodynamic actions and light as a function of water depth (BOUCHON 1981). Geomorphological zonation has been restricted by the lack of a cross-reef energy grad ient during reef formation (KAN et a!. 1995) The different zones and regimes are named according to their most conspicuous faunal or topographical characteri stics (GOREAU & GOREAU 1959). LOVA & SLOBODKIN ( 1971) in thei r study of zonation pattern s at Ei1at, Red Sea, found th at the reef flat region was occupied mainl y by Stylophora and Favia, and the reef crest was occupied predominantly by Echinopora, Acropora and Stylophora in a decreasing order of abundance, and patch reefs were found from 13- 19 m deep. They also found that coral diversity and abundance decreased and stopped between 20-25 m deep. BOUCHON (1980) in his study of the zonati on patterns in the l ordanian Red Sea coast found Zoology in the Middle East 17, 1999: 99-108.

ISS N 0939-7140 © Max Kasparek Verlag . Heidelberg

100

Zoology in the Middle East 17, 1999

that branching corals dominated the 0-20 m zone, massive corals dominated the 20-25 m zone while the encrusting corals dominated the deepest zone of the reef (up to 60 m depth). BOUCHON & LABOREL ( 1990) found that depth and turbidity (linked to a high rate of sedimentation) appeared to be the ecological factors probably controllin g coral distribution and zonation in Grand Cul-de-Sac Marine of Guadeloupe Island . They also found an Acropora cervicornis in the lagoon, a species association on the sea grass beds, a shallow coral community on the barrier reef. a deep comm un ity on the barrier and a community on the deep muddy bottoms of the lagoons. In his study of stony coral distribution in the Gulf

of Cariaco,

ANTONIUS

(1980) found five zones each with one species dominant and some

overlap between them. The purpose of this study is to describe the community structure and diversity as well as the vertical distribution of reef-building corals in terms of zonation and abundance at Ras Umm Seid, Sharm EI-Sheikh, in the Egyptian Red Sea.

Material and methods Ras Umm Seid at Sharm EI-S heikh was chosen for this study (27°50'N, 34° 10' E). A tape of20 m length was la id along the depth contours parallel to the shore (LOVA 1972), at fixed intervals of I m on each of the reef flat and the slope up to II m depth, then every 2 or 3 meters until 25 m depth, then one transect at 30 m depth. Number of individuals (colonies) of each species underlying the transect was calcu lated and divided by the total number of colonies to get the relative abundance. Colony size was measured as the mean of the maximum diameters of all coral colonies of a given species under each transect. An individual is defined as any colony growing independently of its neighbours i.e. whenever an empty space was recorded between two adjacent co lonies (EOMUNDS et al. 1990). When there was any doubt concern ing iden tification of any species, a small piece was collected for later identification. Data of relative abundance and colony diameters were treated by multivariate statistical methods: correspondence analysis CA (GREENACRE 1984) and ascending hierarchic classification AHC (Roux 1985) The computer calcu lations were carried out at the Department of Natura l Resources, Institute of African Research & Studies, University of Cairo, using DATA VISION 1.2 programme (Roux 1987), developed for APPLE lie BASIC. Shannon-Weiner and Simpson indices of diversity were calculated as described by LUDWIG & REYNOLDS ( 1988).

Tab. 1. Numbe r of species (S), and Shannon (H) and Simpson (0) indices of diversity at different depth zones of Ras Umm Seid, Sharm EI-Sheikh.

depth back reef 1-5 m (rIOm 11-15 m 17- 22 m 25-30 m

S 7 13 9 8 8 6

H

1.64 2.43 1.91 1.~ 3

1.85 0.94

D 0.79 0.88 0.82 0.80 0.86 0.55

Coral reefs

101

28%

w

19 14

1

3

w

46

------~~-- 4 ~~~_+--~~~---------------3~fl

10 8

E 31

2 Fig. I . Graphical representation of the results of the application of CA and AHC to the data of relative abundance of corals at Sharm EI-She ikh. Letters A-F =depth zones: A = back reef, B = 1- 5 m, C = 6-10 m, D = I I- I S m, E = 17- 22 m and F = 25- 30 m. Numbers 1- 61 are coral taxa: I, Pocillopora verrucosa; 2, Poci/Jopora damicornis; 3, Montipora spongiosa; 4, Acropora haimei; 5, A.forskali; 6, A. hemperichi; 7, A. humilis; 8, Occu/ina djffusa; 9, Stylophora pislil/ala; 10, Lobophyllia corymbosa; II , L. hemperichi; 12, Ser;alopora heslrix; 13, Platygyra daeda/ia; 14, P. crossland;; 15, Porites compressa; 16, P. (Synaraea) iwayamaensis; 17, P. (s.) undulata; 18, Acanthaslrea echinala; 19, Favia paUida; 20, F. jaus; 21, F. sielligera: 22, F. amicorum; 23 , Favi/esjlexusa; 24, F.s pel's;: 25. Leptoria phrygia; 26, Oulophyllia crispa; 27, Montipora verrucosa; 28, Siderastrea siderea; 29, Goniastrea peelinata; 30, Gaiaxeajascicu/aris; 31, Tub;pora musica; 32, Isophyllaslrea rigida; 33, Gon;opora planulata; 34, Turbinaria mesentrina; 35 , Hydnophora microeonos; 36, Gyrosmilia inlerrupla; 37, Echinopora gemmacea; 38, E. lamellosa; 39, Leptoseris cocullala; 40, Monlipora venosa; 4 1, Pavona decussata; 42 , Heliopora coerolea; 43, Oxypora lacera; 44, Mycdium eiephantotus; 45, Echinophyllia aspera; 46, Millepora dichotoma; 47 , M. comp/anata; 48, Ctenaelis echinata; 49, Fungia concinna; 50, F. danae ; 51 , F. sculari; 52 , Cycloseris distorla; 53 , C. costu/ata; 54, Seriatopora caliendrum; 55 , Anacropora spinosa; 56, Montipora edwardsi; 57, Acropora capillaris; 58, A. pharaonis; 59, A. valenciennes;; 60, A. hyacinthus; 61 , A. nasuta. Points 32, 43 ,44, 45 arc with 3 1, points 12, 17, 27 with 7. point 28 with I I. points 41 , 42, 48 with 15. point 16 with 6, points 21 , 24, 26, 29, 35,40 with 10, point 19 with 20 and point 22 with I.


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Results Shannon (based on relative abundance and relative cove r), Simpson (based on relative abundance) indices of diversity as well as numbers of species are show n in Tab. I. The 1- 5 m depth zone is the most diverse zone of all depth zones. The diversity indices as well as the number of species decrease with in creasing depth . The lowest values were recorded at th e 25-30 m depth zo ne. Fig. I shows results of the application of CA and AHC methods to the data of rel ative abundance. 33% of the total variance is associated with the first (horizontal ) axis and 28% with the second (vertical) one. It is clear th at the first axis se parates the back reef zone and 1- 5 m zone at the left hand side from the other four depth zo nes at the right hand side of the ordination graph. These four depth zones are separated by the vertical axis into two groups: one g roup includes three zones (6-10 m, I I- IS m and 17- 22 m) whil e th e other group includes the 25- 30m zone alone. The back reef zone is more or less characterized by o ne branching species, Pocillopora verrucosa and five massive species, namely Favia amicorum, P/atygyra daeda/ea, Favia pal/ida, F. favus and Faviles j1exusa. T he back reef zone and 1- 5 m depth zone are more or less si milar to each other and characterized by six branchin g corals: Monlipora spongiosa, Acropora haimei, Pocillopora damfcornis, Lobophyl/ia corymbosa, Occulina diffusa and Acropora forskali; fi ve massive co rals: P/atygyra cross/andi, Favia slel/igera, Favites persi, Ou/ophyl/ia crispa and Coniastrea pec/inala; two encrusting corals: Hydnophora micronos and Monlipora venosa; and two hydrocoral spec ies Millepora dicholoma and M. comp/anala. Three depths are similar to each other (6- 10 m, II - IS m and 17- 22 m) and more or less characteri zed by five branching corals: Stylophora pis/illata, Acropora hemperichi, Lobophyl/ia hemperichi, Acropora humilis and Seriatopora heslrix; ten massive corals Tubipora musica, Isophyl/astrea rigida. Poriles ( = Synaraea) ;wayamaensis. Galaxea fascicularis. Lep/oria phrygia. Aeanthastrea echinala. Sideraslrea siderea, Porites compressa, P. undulala and Montipora verrucosa; eight encrusting corals Leploseris cocul/ala. Turbinaria mesentrina. Oxypora lacera, Mycedium elephanrorus. Echinophyllia aspera. Pavona decm'safa, Heliopora coerolea and Echinopora gemmacea and o ne so litary species Crenacris echinala. The deepest zone (25-30 m depth) is more o r less characterized by one massive Goniopora planulala and two encrusting coral species Gyrosmilia interrupra and Echinopora /amel/osa. It is clear the back reef is more or less characterized by higher abu ndance of massive forms while the reef slope is more or less characterized by a decrease of branching corals and increase of massive and encrusting corals with increasing depth . Species of the first group are considered to be highly adapted to the wave exposed areas of the reef flat while species of the second gro up are considered to be tolerant to the waveexposed areas of the reef flat but can tolerate low illumination at hi gher depths. Species of the th ird group are thought not to tolerate the wave-exposed areas of the reef flat but can be adapted both to hi gh illumination at shallower areas of the reef slope and to low illuminati on at deeper areas while species of the fourth group are co nsidered to be highly adapted to low illumination. Fig. 2 shows results of the application of CA and AHC methods to the data of colony diameters. 29% of th e total variance is associated with the first (hori zontal) axis and 25% with the second (vertical) one. Six groups are separated along the second ax is:

103

Coral reefs

25~

7

-

6 2

70

7~

:KJL B 7 3

,,

,,

37

UJ

7.0 378

78

10

5 C 25

1

a §

38

""

. 10

,,

,,

29%

" "- "-

"-

"

73

,

,

I

I I

36

I

""

I

"-

" '-

I

"

I '-

'-

",

I

2 Fig. 2. Graphical representation of the results of the application of CA and AHC to the data of colony diameter of corals at Sharm EI-Sheikh. Symbols of each depth zone and coral species are the same as in Fig. I. Points 42, 48 are with 41 , points 32, 43 , 44, 45 with 31 , point 39 with 38, point 20 with 19, points 21 , 24, 26, 29,35 , 40,47 with 10, points 22, 14 with S, point 23 with 8, point 16 with 6, point 34 with 2, point 46 with 5 and points 12, 17, 27 with 7.

J- The depth zone 11-15 m on the uppermost side of the ordination graph which is more or less characterized by Pavona deeussata, Heliopora eoerolea and Ctenaetis eehinata. 11- The second group is more or less characterized by Lobophyllia hemperichi, Porites eompressa, Acanthastrea echinata and Siderea siderea. These species are more or less characteristic for the depth zones 11 - 15 m and 17- 22 m.

Zoology in the Middle East 17 , 1999

104

111- The depth zone 17- 22 m which is more or less characterized by Tubipora musica, and /sophyllaslrea rigida, Oxypora lacera. Mycedium elephanlolus and Echinophyllia aspera. IV- The depth zones: back reef, 1-5 m and 6-10 m. They are more or less characterised by Acropora humilis, Seria/opara heslrix, Porites undulata, Montipora verrucosa, Acropora forskali, Mil/opara dichotoma, Poeil/opara dimicornis, Turbinaria mesentrina, Acropora hemperichi, Porites iwayamaensis, Echinopora gemmacea, Gcc/ina diffusa, Favites flexusa , Stylophora pistillata, Echinopora /amel/osQ, Leploseris caGulla/a, Favia amicorum, Pfatygyra crosslandi, Poci/lopora verrucosa, Man/ipara spongiosa, Lobophyl/ia corymbosa, Favia stelligera, Favites pel'si, Oulophyllia crispa, Goniastrea pectinata, Hydnophora microconos, Montipora venosa, and MUiepora complanata. V- The fifth group is more or less characterized by the two species: Platygyra daedalea and Gyrosmilia interrupta. The first species is more or less characteristic of the back reef while the second species is more or less characteristic of the two depth zones 1- 5 m and 25- 30 m . VI- The depth zone 25- 30 m which is more or less characterized by Goniopora planula/a. Group IV is more or less characterized by the species which have the lowest colony

diameter at the back reef and the highest colony diameter at 1-5 m which decrease sharply at 6-10 m then decrease gently wherever found at other depth zones until reaching the lowest value at 25- 30 m depth. In groups 1, II & lll, although they represent higher depth zones (11-15 m, 17- 22 m), the species are not more or less characterized by colony diameters which are not so low, and many of them have larger values since they are adapted to low illumination . Groups V &VI are more or less characterized by the species having high colony diameter at 25- 30 m depth where they are considered to be highly adapted to low illumination.

Discussion The present study found that the average number of species recorded in different zones of Ras Umm Seid is highest at 1-5 m zone, and then it decreases with depth. This model of distribution resembles that of STODDART (1969) where a significant decrease in the number of coral species with depth was reported, but differs from that of LoyA (1972) at Elat, Gulf of Aqaba, where a successive increase in the number of species with depth was recorded, except the 12- 19 m zone which exceptionally recorded a lower number of species per transect. The recorded values of Shannon species diversity at Ras Umm Seid are maximum at 1- 5 m zone, then they decrease with depth. BAK (1976) found that the sedimentation which falls from the reef-flat over the slope has a distinguishable effect on coral cover and diversity with depth (both decrease) whilst there is an increase in sediment levels. There is a general decline of diversity with depth but LOYA (1972) showed that there is an initial rise of diversity to a plateau followed by a fall. BOUCHON & LABOREL (1990) stated that depth and turbidity (linked to high rate of sedimentation) are the ecological factors controlling coral distribution and diversity. Sediments reduce the overall amount of substratum available for corals (HODGSON 1990, BABCOCK & DAVIES 1991). The increased abundance of massive forms over other growth forms at both the back reef and the slope at Ras Umm Seid. having clearer water, as shown by CA and AHC, agrees with the result of SHEPPARD (1982) who states that, of the living coral colonies in turbid

Coral reefs

105

water, 55% are ramose whereas 10% are ramose in clearer reefs. Another reason for increasing massive corals rather than branching corals in most depth zones may be because branching corals are more susceptible to breakage caused by trampling than are massive corals (WOODLAND & HOOPER 1977, KAY & LIDDLE 1989). The decrease of branching corals with depth may be because branching corals are poorly adapted to low illumination (JAUBERT 1977). Some evidence exists that, branching corals replace head corals as depth decreases over time (ROGERS 1993). Branched colonies usually decrease with depth and are replaced by encrusting and flattened colonies which have a greater ability to entrap light (BOUCHON 1981, FRICKE & SCHUMACHER 1982). LANG (1970) found that certain species extend their mesentrial filaments and digest any living coral tissue from a colony of another species which they can touch. Deep water species recorded like Oxypora lacera, Mycedium elephantotus and Echinophyllia aspera which do not migrate to shallow water may be considered to develop high specialization to their local environment and have narrower physiological tolerances in comparison to some other species like Pocillopora damicornis, Stylophora pistil/ata, Porites (= Synaraea) iwayamaensis and Echinopora lamel/osa which are recorded both in shallow and deep areas. The recorded species can be divided into 5 categories: • species widely distributed on the reef from the reef flat to the lower part of the reef slope, such as Pocil/opora damicornis, Stylophora pistil/ala, Porites iwayamaensis and Echinopora lamel/osa. • species restricted to the reef flat and the reef slope up to 10 m only, such as Acropora haimei, A. hemperichi, Occulina diffusa and Favites flexusa. They may be considered to be tolerant to the wave~exposed areas of the reef flat but cannot tolerate low illumination at higher depths. • species restricted to the reef slope only up to 5 or 10 m depth, such as Acropora humilis, Lobophyllia corymbosa, Seriatopora hestrix, Porites (= Synaraea) undulata, Favia stelligera and Favites persi. They may be considered not to tolerate the wave exposed areas of the reef flat or low illumination at higher depth s. • species restricted to the reef slope only from 1- 30 m depth, such as Leptoseris cocul/ata (Foliacious coral). It is thought that they do not to tolerate the wave exposed areas of the reef flat but can be adapted both to high illumination at shallower areas of the reef slope and to low illumination at deeper areas. • species restricted to the deeper areas of reef slope only, such as Goniopora planula/a, Oxypora lacera, Mycedium elephanto/us and Echinophyllia aspera which are considered to be highly adapted to low illumination. The present study indicates that the colony size of reef-building species is always lower on the back reef than on the reef slope. A possible explanation for the smaller colony size on the reef flat may be that the reef flat is a relatively unstable, and unpredictable zone compared with the deep reef (LOYA 1972). SLOBODKIN & SANDERS (1 969) defined the severe environment to be the environment which may become completely abi otic with relatively slight environmental change. The present study also demonstrates that the colony size of any given species has its maximum value at 1- 5 m depth (zone of highest illumination) and decreases dramatically at 6- 10 m zone, and then decreases gently with depth at varying degrees for different species. This result ties very well with the results of GOREAU & GOREAU (1959, 1960) who demonstrated, by using calcium-45 and carbon-14 as radioactive tracers and conducting experiments in situ, that calcification in a series of


106

representative corals is, on the average, ten times greater in light than in darkness and the rate of uptake of calcium was even reduced by 50% on cloudy as compared with sunny

days. The decrease of colony size with depth in the studied area resembles that obtained by LOVA (1972) at Eilat where he found a sharp decease in the average colony size from the Millepora zone (0.2-3.0 m) to a depth of 12 m, and then a much less dramatic change between 12 and 30 m. It was found that light influences the deposition of skeletal material over long periods (e.g. KNUTSON et al. 1972). BOUCHON & LABOREL (1990) noted that suspended sediments increase with depth, and thought that this was responsible for the limitation of coral growth by depth . While fecundity increases with colony size, mortality decreases, so that the expected number of future offspring of a genet (its reproductive value) increases throughout its life (HUGHES et al. 1992). The highest amount of broken colonies in the heavily visited sites compared with the less visited sites in Sharm EI-Sheikh indicates that tourism and diving activities are dangerous to corals. Divers may damage reefs by spearfishing (MCMANUS et al. 1981 ), kicking, trampling (HAWKINS & ROBERTS 1992), holding, kneeling or standing on benthic organisms (HAWKINS & ROBERTS 1993). Moreover, the broken and abraded coral tissue is likely to be more susceptible to invasion by pathogens, poss ibly increasing mortality. Unless restrictions are swiftly imposed to slow down the accelerating pace of tourist devel opment in the

northern Red Sea and to cap its u/timate growth, the future of the region s of reefs will remain in doubt (HAWKINS & ROBERTS 1994). The higher amount of damage recorded among branching forms than among other forms in both heavily and less visited sites agrees with the results of WOODLAND & HOOPER ( 1977) and KA v & LIDDLE ( 1989) who concluded that intensive trampling might exert an effect at the community level e.g. by reducing cover of branching corals because these are the most susceptible to breakage while most o f the robust massive colonies survived. The present study has concluded that the amount of broken colonies decreases in the reef crest compared with the outer reef flat and this may be due to the differences in the

morphologies of the corals and the structure of the dead coral substrates between the two zones.

References ANTONIUS, A. (1980): Occurrence and distribution of stony corals in the Gulf of Cariaco, Venezuela. -lnternationale Revue der gesamten Hydrobiologie 65(3): 321 - 338, Berlin. BABCOC K, R. & P. DAVIES (1991): Effects of sedimentation on settlement of Acropora millepora. - Coral Reefs 9: 205- 208. BAK, R. P. M. (1976): The growth of coral colonies and the importance ofcrustose coralline algae and burrowing sponges in relation with carbonate accumulation. - Journal of Sea

Research, Netherlands, 10: 285-337. BOUCHON, C. (1980) Quantitative study of scleractinian coral communities of the Jordanian coast (Gulf of Aqaba, Red Sea): preliminary results. - Tethys 9(3): 243-246. BOUCHON, C. (1981) Quantitative study of the scleractinian coral communities of a fringing reef of Reunion Island (Indian Ocean). - Marine Ecology-Progress Series 4: 273-288.

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BOUCHON, C. and LA BOREL, J. (1990) Les peuplements coralliens du Grand Cul-de-Sac Marine de Guadeloupe (Antilles Fran9aises). - Annales de I' lnstitut Oceanographique 66(1-2): 19-36, Paris. EDMUNDS, P. J., D. A. ROBERTS & R. SINGER (1990): Reefs of the northern Caribbean. I. Scleractinian populations. - Bulletin of Marine Sciences 46(3): 780-789, Coral Gables. FRICKE, H. W. & H. SCHUHMACHER (1982): The depth limits of Red Sea stony corals, an . ecophysiological problem (a deep diving survey of submersible). - Marine Ecology, Pubblicazioni della stazione zoologica di Napoli 4(2): 163- 194, Naples. GOREAU, T. F. & N. I. GOREAU (1959): The physiology of skeleton formation in corals. II. Calcium deposition by hermatypic corals under various conditions in the reef. Biological Bulletin, Marine Biological Laboratory, 117: 239-250, Woods Hole. GOREAU, T. F. & N. I. GOREAU (1960): The physiology of skeleton formation in corals. III. Calcification rate as a function of colony weight and total nitrogen content in the reef coral Mancina areo/ala (Linnaeus). - Biological Bulletin, Marine Biological Laboratory, 118: 41 9-429, Woods Hole. GREENACRE, M. J. ( 1984). Theory and application of correspondence analysis. - London, 363 pp. HAWKINS, J. P. & C. M. ROBERTS (1992): Effect of recreational SCUBA diving on fore-reef slope communities of coral reefs. - Biological Conservation 62: 171- 178 . HAWKINS, J. P. & c. M. ROBERTS (1993): Effects of recreational SCUBA diving on coral reefs trampling on reef flat communities. - Journal of Applied Ecology 30(1): 25- 30, Oxford. HAWKINS, J. P. & c. M. ROBERTS (1994): The growth of coastal touri sm in the Red Sea: Present and future effects on coral reefs. - Ambio 23(8): 503- 508 . HODGSON, G. (1990): Sediment and settlement of larvae of the reef coral Pocilloporo damicornis. - Coral Reefs 9: 41-43. HUGHES, T. P., D. ARYE & J. H. CONNELL (1992): The evolutionary ecology of corals. Tree 7(9): 292-295. JAUBERT, J. (1977): Light, metabolism and growth forms of the hermatypic scleractinian coral Synaraea convexa Verill in the lagoon of Moorea (French Polynesia) . Proceedings of the 3rd International Coral Reefs Symposium I: 483-488, Miami. KAN, H., N. HORl, Y. NAKASHIMA & K. ICHIKAWA (1995): The evolution of narrow reef flats at high-altitude in the Ryukyu Islands. - Coral Reefs 14: 123- 130. KAY, A. M. & M. J. LIDDLE ( 1989): Impact of human trampling in different zones ofa coral reef flat. - Environmental Management 4: 509- 520. KNUTSON, D. W., R. W. BUDDEMEIR & S. V. SMITH ( 1972): Coral chronometers, seasonal growth bands in reef corals. - Science 177: 270-272, New York . LANG, J. C. (1970): Interspecific aggression within the scleractinian reef corals. - Ph. D. thesis, Yale University. LOY A, Y. (1972): Community structure and species diversity of hermatypic corals at Eilat, Red Sea. - Marine Biology 13: 100-123, Berlin. LOYA, Y. & L. B. SLOBODKIN (1971): The coral reefs of Eilat (Gulf of Eilat, Red Sea).Symposia of the Zoological Society of London 28: 117- 139, London. LUDWIG, J. A. & J. F. REYNOLDS (1988): Statistical Ecology: A primer on methods and computing. - New York, 337 pp.

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MCMANUS, J. W., R. l. MICLAT & V. P. PALAGNAAS (1981): Coral and fish community structure of Sombrero Island, Batangas, Philippines. - Proceedings of the 4th International Coral Reefs Symposium 2: 271-279, Manila. ROGERS, C. S. (1993): Hurricanes and coral reefs: the intermediate disturbance hypothesis revisited. - Coral Reefs 12: 127-137. Roux, M. (1985): Algorithmes de Classification. - Paris, 151 pp. Roux, M. (1987): DATA VISION 1.2 logociel d'analyse de donnees. - Montpellier, 30 pp. SHEPPARD, C. R. C. (1982): Coral population on reef slopes and their major controls. Marine Ecology-Progress Series 7: 83- 11 5. SLOBODKlN, L. B. & H. L. SANDERS ( 1969): On the contribution of environmental predictability to species diversity. Diversity and stability in ecological system. Brookhaven Symposia in Biology 22: 82- 95, Brookhaven. STODDART, D. R. (1969): Ecology and morphology of recent coral reefs. - Biological Reviews 44: 433-498, Cambridge. WOODLAND, D. J. & N. A. HOOPER ( 1977): The effect of human trampling on coral reefs. Biological Conservation 11: 1-4.

Authors' addresses: Prof. Dr. Sayed A. K. Abo-Hegab, Department of Zoology, Faculty of Science, University of Cairo, 12613 Giza. Egypt. - Prof. Dr. Wafai Z. A. Mikhail, Department of Natural Resources, Institute of African Research & Studies, University of Cairo, 12613 Giza, Egypt. - Dr. Mohammed S. A. Ammar, National Institute of Oceanography and Fisheries, Suez, P.O. Box 182, Egypt.