Mar. Ecol. Prog. Ser. Coral communities of the Namsu Islands (Gulf of Siam, South China Sea) Yu. Ya. Latypov

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1 Vol. 9: 6-70, 986 l MARINE ECOLOGY - PROGRESS SERIES Published March 6 Mar. Ecol. Prog. Ser. Coral communities of the Namsu Islands (Gulf of Siam, South China Sea) Yu. Ya. Latypov Institute of Marine Biology, Far Science Center, Academy of Sciences of the USSR, Vladivostok 6900, USSR ABSTRACT: Fringing reefs of the Namsu Archipelago (Gulf of Siam) were studied using quadrat and transect techniques. Five zones were distinguished which may be compared with or related to boat channel, inner and outer reef flat, reef slope and sloping platform. The degree of affinity of communities in different zones was analyzed. On the basis of variations in quantitative distribution of the corals, groups of scleractinian corals were separated in terms of ecological requirements: species widespread from intertidal zone down to a reef slope; species of the lower part of a reef slope; and species inhabiting the sloping platform. In the reef studied, species of Scleractinia (6 genera) and Hydrocorallia ( genus) were found. INTRODUCTION AND REEF MORPHOLOGY The Namsu Archipelago (9'0' N, 0" E) includes islands and rocks forming groups separated by a ca l-mile-wide pass (Fig. ). The islands consist of acid and basic effusive, effusive-sedimentary and sedimentary deposits of the Middle Paleozoic. Tufas and tuff conglomerates predominate. Recent deposits on beaches and isthmuses are of block-and-boulder, boulder-and-pebble and sand substrata, sometimes with a considerable admixture of shell and coral debris. Underwater slopes of the islands are fringed with block-pebble deposits replaced with increasing depth by shingle, gravel and finally coarse sand intermingled with abundant organic detritus. At a depth of 6 to 0 m (0 to 00 m from the shore line), the slightly inclined sloping platform is covered by silty sand and fine-grained silt deposits with a considerable admixture of organic detritus. The reefs and corals here have not previously been studied. Five different zones with scleractinian communities and considerable growth of the hydroids Millepora platyphylla and zoanthids Zoanthus sp. have been distinguished in the reef structure (Fig. to ). From a morphological standpoint, the first zone ('algal-coral') starts from the intertidal zone. It includes separate scleractinian colonies, mostly of massive encrusting form. Millepora and Zoanthus form crustose colonies; sparse growths of Turbinaria and the alga Laurencia inhabit rocky substrata and blocks. This zone is l to 0 m wide and up to m deep. The second morphological zone ('polyspecific settlement') is formed mostly by assemblages of polyspecific Fig.. (A) Location of Namsu Islands in the Gulf of Siam (B) Location of the reefs and transects ( to 8) O Inter-Research/Printed in F. R. Germany /86/009/06/$ 0.00

2 Colonies - N O m m $ 0 : g o p,

3 Latypov: Coral communities of Namsu Islands 6 Coverage Fig.. Cross section on the reef Botcha (Transect 8) 0 Proportion of different forms Massive forms Branch~ng forms --- Encrust~ng forms scleractinian colonies of different growth forms with encrusting and weakly branched colonies of Millepora, sometimes also with Zoanthus. The substratum of the second zone contains boulders and pebbles of terrestrial origin, coral and shell debris. It is about 0 m wide and m deep. The third zone ('monospecific settlement') where corals are dominant, is almost completely formed by a monospecific population or by to scleractinian species. The substratum consists of dead coral colonies, coral debris, overgrown pebbles, and organic detritus of various origin. The zone is to 0 m wide and to 7 m deep. The fourth zone, of Alcyonacea and coral, occupies the well-differentiated reef slope, inhabited by separate scleractinian colonies, soft corals and Gorgonacea attached to hard portions of a generally silty substratum. The zone is 0 to 60 m wide and 6 to m deep. The fifth zone lies on the sloping platform and is characterized by single colonies of Alcyonacea, Scleractinia and Gorgonacea mixed with a few solitary corals. Sparse growth of algae Halophila occurs frequently here. MATERIALS AND METHODS The distribution of scleractinian corals was studied quantitatively by the transect and quadrat techniques of Loya & Slobodkin (97), Maragos (97), Maragos & Jokiel (976), and Bouchon (98) on 8 cross-sections of the islands mentioned above (Fig. ). The profile of each transect was established and the boundaries of bionomical zones marked. The coverage of the substratum was studied according to Maragos & Jokiel (976) with the number of dominant taxa (genera and species) registered. The proportion of massive, branching, and encrusting coral forms was recorded for every m of transect. Qualitative samples of Scleractinia were taken in every physiographic zone. The coefficient of affinity between different zones, and between sides of the reefs (i.e. between different transects on the same island), was evaluated using Jaccard's index (90). Scleractinia species were identified by the author using descriptions of Crossland (9), Chevalier (97: 97), Veron & Pichon (976, 979, 98), and Veron & Wallace (98). RESULTS Eight transects were run from the islands, on both inner and outer sides of the archipelago (Fig. ). Namsu Island, the largest in the archipelago, was not surveyed. Its reefs are apparently unrepresentative because of severe anthropogenic impact. All the reefs studied have generally the same morphological structure and zonation. The fringing reefs form a crust covering the substratum at a distance of 0 to 00 m from the shore around the islands and sea rocks. A total of species belonging to Scleractinia (6 genera) and Hydrocorallia ( genus) were sampled during the study (Table ). Species diversity and the degree of similarity between coral communities in different zones made it possible to distinguish Scleractinia assemblages in the Namsu Archipelago reefs: () a community of the 'boat channel', () a community of the 'reef flat', () a community of the reef slope, and () a community of the sloping platform. The reef morphology terms and the principles of zonation

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5 Latypov: Coral communities of Namsu Islands 6 Table. Continued Species Zyan North Zyan Mok Transect no. Mok West 6 West 7 Southeast 8 Botcha F. echinata (Pallas 766) Herpolita limax (Houttuyn 77) Polyphyllia talpina (Lamarck 80) Podobacia crustacea (Pallas 766) Porites lobata Dana 86 P. murrayensisvaughan 98 P. australiensis Vaughan 98 P. lutea Edwards & Haime 98 P. stephensoni Crossland 9 P. densa Vaughan 98 P. rus (Forskbl77) Goniopora stokes Edwards & Haime 8 G. lobata Edwards & Haime 860 G. columna Dana 86 G. djiboutiensisvaughan 907 G. pandoraensis Veron & Pichon 98 G. stutchbujyi Wells 9 Alveopora allingi Hoffmeister 9 Favia stelligera (Dana 86) F. favus (Forskbl 7) F. speciosa (Dana 86) F. pallida (Dana 86) F. amicorum (Edwards& Haime 80) F. matthaivaughan 98 F. rotumana (Gardiner 899) F. laxa (Klunzinger 879) F. maxrma Veron & Pichon 977 F. lizardensis Veron & Pichon 977 Favia sp. Favites chinensis (Verrill 866) F. abdita (Ellis& Solander 786) F. flexuosa (Dana 86) F. rotundata Veron & Pichon 977 Goniastrea edwardsi Chevalier 97 G. retiformis (Lamarck 86) G. aspera (Verrill 86) C. pectinata (Ehrenberg 8) Platygyra daedalia (Ellis& Solander 786) P. lamelljna (Ehrenberg 8) P. sinensjs (Edwards& Haime 89) P. pini Chevalier 97 Oulophyllia crispa (Lamarck 86) Leptoria phrygia (Ellis& Solander 786) Hydnophora rigida (Dana 86) H. exesa (Pallas 766) H. rnicroconos (Lamarck 86) Oulastrea crispata (Lamarck 86) Leptastrea purpurea (Dana 86) L. transversa Klunzinger 879 L. pruniosa Crossland 9 Cyphastrea serailia (Forskbl 77) C. chalcidicum (Forskbl 77) Echinopora lamellosa (Esper 79) E. hirsutissima Edwards & Hairne 89 Trachyphyllia geoffroyi (Audouin 86) Galaxea astreata (Lamarck 86)

6 66 Mar. Ecol. Prog. Ser. 9: 6-70, 986 Table. Continued Species Zyan North Zyan Mok Transect Mok West no. 6 West 7 Southeast 8 Botcha G. fascicularis (Linnaeus 797) Lobophyllia hemprichii (Ehrenberg 8) L. coryrnbosa (Forskal 77) L. costata (Dana 86) L. hattaiyabe, Sugiyma & Equchi 96 Symph yllia recta (Dana 86) S. radians Edwards & Haime 89 S. valenciennessi Edwards & Haime Euphyllia fimbriata (Spengler 799) Plerogyra sinuosa (Dana 86) Turbinaria peltata (Esper 79) T. frondens (Dana 86) T. reniformis Bernard 896 T. mesenterina (Lamarck 86) T. crater(palas 766) T contorta Bernard 896 T. radicalis Bernard 896 T patula (Dana 86) T. stellulata (Lamarck 86) Heteropsammia cochlea (Spengler 78) Bathyactis palifera Lamarck 8 6 Heterocyathus aequiscostatus Edwards & Haime 89 Hydrocorallia Millepora platyphylla Hemrich & Ehrenberg 8 M. dichotoma Forskal 77 Number of species In transect In reef Number of common species Between transects Between reefs used in the study were defined by Picard (967), Battis- millepora and Millepora platyphyla were the next tini et al. (97) and Bouchon (98). most abundant species. The rank order of abundance The results concerning distribution of different of different corals in each zone measured by percentbranching, massive and encrusting growth forms on age of coral coverage is presented in Fig. 6. the reef and variations in the degree of coverage are presented in Fig. to. The proportions of massive, branching and encrusting forms in the coral coverage 'Boat channel' community are shown for the cross-sections of the reefs and are clear from these figures without additional discussion. The shore zone is exposed to maximal wave action Although species diversity (Table ) in all transects and light intensity. The coral community of this zone is was relatively high and varied between 6 and 67 usually formed by species typical of boat channel and species, the communities were dominated by the same reef flat: Pocillopora verrucosa, Psammocora contigua, several species. Porites australiensis and P. murra- Acropora millepora, A. digitifera, Goniastrea retiforyensis were generally most abundant. Galaxea fas- mis, Millepora platyphylla and encrusting colonies of cicularis, Turbinaria peltata, Acropora cytherea, A. Zoanthus sp. (from to species). Coral coverage is

7 Latypov: Coral communities of Namsu Islands 67 A B Acropora cytherea or A. millepora B [mrmj Astreopora ocelata C Montipora foliosa or M. composita D Porites australiensis or P. murrayensis E Goniopora stokes; F Goniastrea retiformis G Leptoria phrygja, Galaxea fascicularis MS I SR l SP,, m Hydnophora exesa J Turbinaria peltata K m Millepora platyphylla L m Zoanthussp. M B Heteropsammia cochlea N m Antipataria sp. 00 Favia speciosa p B Fungia paumotensis AC PS I MS I SR I S P Fig. 6. Structure of coral communities as measured by percent coral cover and rank order of abundance species for islands Mok, Zyan, and Botcha (Transects,, & 8 respectively) seldom above 0 %. Maximal coverage is attained by Zoanthus sp. (0 %), Acropora ( %), Millepora platyphylla ( %), Leptoria (6 %), and Porites (. %). The growths of Turbinaria decurres and the alga Laurencia sp. seldom cover more than 0% of the substratum. In general appearance and species composition of coral and algal coverage, the zone looks very similar to the boat channel defined by Bouchon (98). 'Reef flat' community This community is generally characterized by one or two species of dominant scleractinians. In this community an inner and an outer part can be distinguished, which differ in dominant species, some of them occupying only limited reef areas. The inner part of this community differs from the previous 'boat channel' community by the appearance

8 Mar. Ecol. Prog. Ser. 9: 6-70, 986 of large branching and massive colonies and by small monospecific settlements. A mosaic pattern of coral settlements is very typical of this reef part. Coral coverage ranges from 0 to 00 %. The dominant genera are Acropora ( to %), Galaxea (8 to %), Leptoria ( to 0 %), Montipora ( %) and the hydroid Millepora (8 to %). A total of to scleractinian species occur in this subzone. A prominent feature of the inner part community is the development of small monospecific settlements of Acropora cytherea and Galaxea fascicularis. The outer part is distinguished by the development of continuous monospecific settlements of corals typical of the reef flat and includes 0 to 7 scleractinian species. The reef flat is usually covered by Acropora growths but the Namsu reefs are dominated mostly by Porites murrayensis (8 to 00%) and Galaxea fascicularis (0 to 00 %). Turbinaria peltata, T. rnesenterina ( to 6 %), Acropora millepora (0 to "h), Montipora foliosa ( to 6 %), M. hispida ( to 0 %), Goniastrea retiformis (6 to %) and Favia speciosa ( to %) are common here. The degree of coverage by corals is usually high (60 to 00 %) and seldom below 0 %. Vast areas (several tens of square metres) covered with Galaxea and Turbinaria colonies are coalescent with large massive colonies of Porites. The inner and outer parts of the zone with their respective Scleractinia communities were found to be similar in several dominant species and in the community structure to the inner and outer parts of the reef flat described by Loya (97), Pichon (97) and Bouchon (98). Reef slope communily Reef slope communities have been described by many authors: Picard (967), Pichon (97), Faure & Montaggioni (976) and Bouchon (98). The reef slope community of the islands studied is remarkable for its high coral diversity and richness in growth forms. The species found here are either widespread or restricted to this zone only. Species with a wide distribution are Acropora rnillepora, Montipora hispida, Pavona decussata, Porites lutea, Favia speciosa, Platygyra daedalea, and Goniastrea fascicularis. The species Pseudosiderastrea tayamai, Goniopora columna, Alveopora allingi, Oulastrea crispata, Leptastrea pruniosa and Trachyphyllia geoffroyi seem to prefer this particular zone of weaker light and wave action. The lower levels ot the reef slope are occupied by numerous colonies of Alcyonacea, Gorgonacea and Antipatharia. A total of to 9 scleractinian species occurred in the zone. The coverage rate varied in the range to 60%, approaching 00% in the sites occupied by monospecific settlements. The highest percentage of coverage is contributed by dominant Porjtes ( to %), Montipora (6 to 0 %), Astreopora (6 %), Turbinaria ( %) and Fungia ( to specimens per m). The lower level of the reef slope supported small separate colonies of Turbinaria peltata, Psammocora profundacella, Astreopora ocellata, Coscinarea columna, Fungia paumotensis and Trachyphyllia geoffroyi. Sloping plaff orm community A low rate of coverage (several percent and fractions of percent) and suppressed, small and scattered colonies of about a dozen Scleractinia species are typical of the zone. Representatives of Leptoseris, Goniopora, Leptastrea, Loboph yllia, Symph yllia, Trach yph yllia and Turbinaria which are common for deep sites with low light intensity inhabit this peripheral reef part. The sloping platform of the Namsu reef is distinguished by the development of small single scleractinian corals Heteropsammia cochlea and Bathyactis palifera (up to 00 to 800 specimens per m') with tufts of the grass Halophila decipiens scattered between them. Glynn (97), Faure (977), Bouchon (98) and other authors have reported the scarcity of vegetation on the sloping platform. DISCUSSION AND CONCLUSION Qualitative diversity of Scleractinia in different reef zones and reef zone parts was expressed through the degree of similarity (number of common species). The various reef zones contained from 0 to 6 species in common. Adjoining zones supported the greatest number of common species. The greatest similarity is typically found in the coastal zones: to % of common species in the 'algal-coral' and 'polyspecific settlement' zones, 6. to 6. % in 'polyspecific' and 'monospecific' settlements, and. to 8.6 % in the 'algal-coral' and 'monospecific' settlements. A far lower similarity (.8 to.8 %) was found between the species compositions of the 'monospecifi.~' settlement and the 'reef slope'. Very few or no common species were found in zones remote from each other. The 'algal-coral' zone and the 'sloping platform' had 0 to % and the 'polyspecific settlement' zone and the 'sloping platform' supported 0 to 7 % species in common. Coastal zones were inhabited by common reef corals adapted to a wide range of ecological conditions. The reef slope zone always supports some specific and some widespread reef species. Similar and other characteristics of the slope communities have been given by Loya (97), Pichon (97), Maragos (97), Faure (977) and Bouchon (98).

9 Latypov: Coral comm,unities of Namsu Islands 69 The degree of affinity expressed by the number of common species between different sides of reefs was high, 6.8 to 6. %. The reefs of separate islands had nearly 60% species in common. This may be explained by noting that the Namsu reef zones can be only conventionally compared to lagoons (boat channel) or reef flat. On Namsu reefs there are no lagoons or boat channels separated by a reef flat and also no reefflat platform. An exception is the southeastern side of Island, where we observed shallow reef-parts which were morphologically similar to a lagoon or reef flat and contained combinations of taxa and growth forms of scleractinians and algae usually typical of these zones. Coastal zones of the southeastern part of reef have 7. to 9. % of common species. This is consistent with the coefficients of similarity of other reef zones with typical zonality, which possess no more than 0 % species in common (Bouchon 98). On the Jang Bo reef in the Fukhang Province of South Vietnam, all the typical zones show a high degree of similarity: 6.88 to 7. % of species in common. Similar affinity is found for scleractinian communities of various zones of more than 0 other reefs of the province. Qualitative diversity of Scleractinia over a reef shows different ecological requirements of coral species. For Namsu reefs we have established groups of corals in terms of their adaptation to different wave action and illumination: () Coral species widespread from the lower horizon of the intertidal zone down to a reef slope: Pocillopora damicornis, Acropora millepora, Montipora hispida, Galaxea fascicularis, and Goniastrea retiformis. () Coral species inhabiting the lower part of the reef slope and adapted to weaker illumination: Pseudosiderastrea tayamai, Goniopora colurnna, Alveopora allingi, Oulastrea crispata, Leptastrea pruniosa and Fungia pa umotensis. () Coral species inhabiting the sloping platform and adapted to limited illumination: Trachyphyllia geoffroyi, Montipora subtilis, Turbinaria peltata, Heteropsarnmia cochlea and Bathyactis palifera. Zones of intensive wave action are inhabited by Acropora rotumana, A. robusta, Fa via pallida, Goniastrea retiformis and the hydrocoral Millepora platyphylla. The following genera show the greatest species diversity: Acropora ( species), Favia ( species), Montipora (0 species), Turbinaria (9 species) and Porites (7 species). These genera are responsible for the maximal coverage and development of monospecific settlements occupying vast areas, but their contributions vary. The densest and largest settlements are formed by Porites and Galaxea, which often occupy 00 % of the available area. Turbinaria and Acropora are responsible for 6 and % of coverage, respectively, and Montipora cover up to 0 % of the substratum. Encrusting colonies of Millepora and Zoanthus cover small areas in the coastal zone. Acknowledgements. The author extends his sincere thanks to the Administration of the Institute of Marine Research (NCSR, SRV) headed by Dr. Le Tchong Fan and to Dr. Nguen Kim Hung, the Head of the Vietnamese part of the Program of cooperative research, and to co-workers of the Laboratory of Hydrobiology of the IMR for their support and careful attention during this survey. The author thanks also Dr. Eugene V. Krasnov for critical reading of the manuscript and Irina A. Barsegova for preparing the English text of the paper. LITERATURE ClTED Battistini, R., Bourrouilh, F., Chevalier, J. P,, Coudray, J., Denizot, M,, Faure, G., Fisher, J. C., Guilcher, A., Hermelin-Vivien, M,, Jaubert, J., Laborel, J., Montaggioni, L., Masse, J. P., Mauge, L. A., Peyrot-Clausade, M,, Pichon, M,, Plante, R., Plaziot, J. C., Plessis, Y. B., Richard, G., Salvat, B., Thomassin, B. A., Vasseur, P., Weydert, P. (97). 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Indonesia 7: 7-97 Faure, G., Montaggioni, L. (976). Les recifs coralliens au vent de l'ile Maurice (Archipel des Mascareignes, Ocean Indien): Geomorphologie et bionomie de la pente externe. Mar. Geol. : 9-6 Glynn, P. W. (97). Rolling stones among the Scleractinla: Mobile coralith communities in the Gulf of Panama. Proc. nd Int. Coral Reef Symp. : 8-98 Grigg, R. W. (98). Community structure, succession and development of coral reefs in Hawaii. Mar. Ecol. Prog. Ser. : - Jaccard, P. (90). Lois de destribution florale dans la zone alpine. Bull. Soc. vaud. Sci. nat. 8: 69-0 Loya, Y. (97). Community structure and species diversity of hermatypic corals at Eilat (Red Sea). Mar. Biol. (): 00- Loya, Y., Slobodkin, L. (97). The coral reefs of Eilat (Gulf of Eilat, Red Sea). Syrnp. 00. Soc. Lond. 8: 7-0 Maragos, M. (97). Coral communities on a seaward reef slope, Fanning Island Pacif. Sci. 8(): 7-78 Maragos, J. E., Jokiel, P. L. (976). Reef corals of Canton Atoll:

10 Mar. Ecol. Prog. Ser. 9: Local distribution. In: An environmental survey of Canton Atoll lagoon, 97. Naval Undersea Research, NCV. 9: -9 Picard, J. (967). Essai de classement des grands types de peuplements rnarins benthiques tropicaux, d'aprhs les observations effectuees dans les parages de TulCar (Sud Ouest de Madagascar). Recl. Trav. Stn mar. Endoume (fasc. hors s6r.) G(Supp.): - Pichon, M. (97). Comparative study of the main features of some coral reefs of Madagascar. La Reunion and Mauritius. Symp. zool. Soc. Lond. 8: 8-6 Veron, J. E., Pichon, M. (976). Scleractinia of ern Australia. Part I. Families Thamnasteriidae, Astrocoeniidae, Pocilloporidae. (979). Part. Families Agariciidae, Siderastreidae, Fungiidae, Oculinidae, Merulinidae, Mussidae, Pectiniidae, Caryophyllidae, Dendrophyllidae. (98). Part IV. Family Poritidae. Australian Institute of Marine Science Monograph Series Veron, J. E. N., Wallace, C. C. (98). Scleractinia of ern Australia. Part V. Family Acroporidae. Australian Institute of Marine Science Monograph Series This article was submitted to the editor; it was accepted for printing on December 9. 98