Barrier and Platform Reefs of the Vietnamese Coast of the South China Sea

Yuri Yakovlevich Latypov

Barrier and Platform Reefs of the Vietnamese Coast of the South China Sea

Yuri Yakovlevich Latypov

A.V. Zhirmunsky Institute of Marine Biology, FEB-RAS, Vladivostok, 690059, Russia

Author

Correspondence author
International Journal of Marine Science, 2013, Vol. 3, No. 4 doi: 10.5376/ijms.2013.03.0004
Received: 02 Dec., 2012 Accepted: 11 Jan., 2013 Published: 11 Jan., 2013

This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Preferred citation for this article:

Latypov, 2013, Barrier and Platform Reefs of the Vietnamese Coast of the South China Sea, International Journal of Marine Science, Vol.3, No.4 23-32 (doi: 10.5376/ijms.2013.03.0004)

Abstract

The composition and spatial distribution of the coral communities of the barrier reefs of Giang Bo, Ly Son island and the platform reef at Bach Long Vi Island were described in detail for the first time for Vietnamese waters. In common, more 260 species of corals and their accompanying species of macrobenthos were found. Acroporids, poritids, and mussids among the scleractinian corals dominated. Monospecific aggregations of Alcyonarian Sinularia and Lobophytum and the hydroid Millepora were rather numerous. Based on its geomorphological characteristics, coral species diversity and zonal distribution, the reefs of entire area are comparable with ribbon and platform reefs on the Great Barrier Reef in Australia and to the barrier reefs of the Philippines and Indian Ocean.

Keywords

Coral reef; Species composition; Structure; Vietnam

Continuous attention has been paid to the coral communities of Vietnam since the research of Serene (1937) and Dawydoff (1952). Since 1980s, Russian, Japanese and Vietnamese scientists, including those under the aegis of the WWF (Ken, 1991; Latypov, 1982, 1987, 1992, 1995, 2000, 2011; Vo and Hodgson, 1997; Yet, 1997; WWF, 1994), have systematically studied Vietnamese reefs. Various types of reef, their communities and the biology of several inhabitants (Latypov, 1986, 1993, 2000; Sakai et al., 1986; Vo et al., 1997) were described during that period; however, the barrier reefs and platform reef of Vietnam were only briefly noted in Latypov’s monograph (see Latypov, 2007). During the past ten years we had an opportunity to repeatedly visit the barrier reefs of Central (Ly Son island) and South (Giang Bo Reef) Vietnam. In 2007 on the 34^th cruise of the Research Vessel “Akademik Oparin” , I was fortunate to visit and investigate the coral reef of Bach Long Vi Island situated in the southern part of the Gulf of Tonkin (20º08′ N, 107º44′ E). Based on its large size (7.5~8.0 km in length and more than 4.5 km in width), variable morphology, and the presence of a very small lagoon, this reef can be classified as the platform reef type. Barrier and platform reefs are interesting in that they are not exposed to intense anthropogenic press and remained in satisfactory or good condition. They have high species richness and are intense of substrate covering by living corals. Giang Bo reef is located in open bay and is under the influence of winds from all directions. Due to the almost constant waves, it difficult to access for small fishing boats and easily equipped with divers. Ly Son island is more than 15 miles from the coast and large settlements. The population of a small village on the island is occupied mainly the cultivation of garlic. Therefore, the Island Reef is not subject to severe human impacts. Bach Long Vi Island is located in the open part of the Gulf of Tonkin. It dispersed a small garrison of the Vietnamese army. For this reason, the approach to the island closer than two miles prohibited. Reefs of the island, the most preserved of all Vietnamese reefs in its natural state. Taking into account the insufficiency of information, we gave detailed descriptions of the coral communities of these reefs, which significantly complemented the general characteristics of the structural organization and spatial distribution of the population of Vietnamese reefs.

1 Results and Discussion

1.1 Giang Bo Reef

The south–north transects (Figure 1). The bottom area adjoining to the reef base at a depth of 17 m was a flat platform with silt–sand sediments with debris of invertebrate skeletons. The depth gradually decreased by 1.5~2.0 m from the 40th to the 100th meter of the transect. Massive and sporadic encrusting colonies of scleractinian occurred. Colonies of Heliopora occurred most often, Pachyseris, Mycedium, Pavona, Montipora, Podobacia, Goniopora, Alveopora, Lobophyllum, Pectinia, and Euphyllia were rather common, Galaxea, Herpolitha, Fungia, Polyphyllia, and large colonies Porites were sometimes recorded, and Acropora and small of branching Porites occurred sporadically. The coral covering of the substrate was 7–10%. The associated macrofauna presented by singular individuals of the bivalve mollusks Atrina vexillum and Malleus malleus and of the sea stars Linckia laevigata and Culcita novaeguineae. The latter two species also recorded in the same numbers in all other zones of the reef. At the distance of 100–160 m from the beginning of the transect, the percentage of coral covering of substrate pronouncedly increased, from 10 up to 72%, with the same thing occurring to the size of colonies and species diversity of scleractinian Acropora most of all.

Figure 1 The cross-section profile of Giang Bo Reef

The buttress system began from the 160th meter of the transect (Figure 2). The species diversity of the corals sharply increased (by 1.5 times) concurrently with the variety of their growth forms. The coral covering of substrate increased to 100%. Young settlements of scleractinian rather often occurred on an old lamellar colony of Acropora of a 100×60 cm area (Table 1).

Figure 2 Structure of corals settlements at buttress system on the reef Giang Bo (depth 12 m)

Table 1 Settlements of small coral on dead lamellar Acropora

This zone extended almost to 70 m. The following approximately 40 m of the transect were a zone of Acropora, in which monospecies settlements of A. cytherea, A. hyacinthus, A. formosa, and Porites rus with individual colonies of Goniastrea, Astreopora, Pocillopora, Montipora, Heliopora, and massive forms of Porites, were clearly distinguished.

At a depth of 3~5 m, at the 240th~250th meter of transect, the reef flat zone extending by 200~300 m began with individual channels. It characterized by a continuous covering of substrate by corals (Figure 3) and interrupted by hollows oriented from northeast to southwest. The ample tangled settlements, up to 100~150 m wide, were composed of A. cytherea, A. hyacinthus, A. formosa, P. rus, Montipora aequituberculata, the seaweed Chnoospora implexa and sea mat Zoanthus sp. Individual colonies of scleractinian and small bioherms spread in channels of sand sediments. The holothurian Holothuria atra (0.2 ind./m²), the bivalves Tridacna crocea (up to 2 ind./m²), and T. squamosa (up to 0.1 ind./m²) were the most abundant of the associated fauna, including the gastropods Cymatium spp. and Oliva spp. (up to 3 ind./m²) occurring in the sand.

Figure 3 Monospecies population of Acropa on reef flat of the reef Giang Bo (depth 1 m)

Corals were associated with bivalves, with domination of Arca ventricosa (10~15 ind./m²) and Beguina semiorbiculata (up to 10 ind./m²), common Septifer bilocularis, Pinctada margaritifera and Cardita variegata, as well as the gastropods Tectus niloticus, Trochus maculates and Turbo petholatus (Table 2). The projective cover of substrate by corals varied from 10% up to 100% and included more than 100 species in its composition.

Table 2 Associated flora and fauna on investigated reefs

From the 670th to the 673rd meter of the transect, in a rather limited bottom area at a depth of 9~11 m, large colonies of A. formosa and A. florida up to 2.5 m in diameter with clumps of fungiid in between were replaced by settlements of A. formosa with infundibular M. aequituberculata and lamellar–ramose Merulina ampliata reaching 1.5 m in diameter. The percentage of coral covering of the substrate sharply decreased with 680th meter of the transect, and the species composition of corals was reduced by almost 2 times. The coral settlements looked like individual patches of several colonies. Rather small bioherms sometimes occurred. By the 700th meter of the transect at a depth of about 9 m only individual scleractinian or bunches of 3~5 colonies, whose projective cover of the bottom was about 3%~7% occurred.

The settlements mostly consisted of Acropora (4~5 species), Millepora (2 species), Porites (3 species) and few species of Goniopora, Galaxea, Symphyllia, Mycedium, Goniastrea, Leptastrea, Montipora, Stylophora, Pocillopora and Turbinaria genera. Sometimes individual colonies of alcyonarians and gorgonarians occurred. Sparse bivalves and gastropods (A. vexillum, M. malleus, Pteria penguin, Chicoreus ramosus, Ch. microphyllus), sea lilies and some other invertebrates were recorded in the associated fauna.

The west–east transect. At the beginning of the transect oriented from the shore to the open sea, at depth of 4.5 m, an extended area of scrap of dead corals was observed. Small, up to 10 cm diameter, individual colonies of Pocillopora, Stylophora, Acropora (A. palifera, A. humilis, A. millepora, and A. florida), Montipora, Porites, Leptoria, Platygyra, Pavona, Hydnopohora, Favia, and Favites occurred for the next 50 m. The projective coral covering of bottom was 10%~15%. There were also numerous dead lamellar colonies of Acropora up to 2 m in size. Between the 140th and 150th meter of the transect Stylophora pistillata dominated among corals in its frequency of occurrence. Further, the zone of settlements of Acropora, Porites and the alga Chnoospora was spread; the projective cover of the bottom was about 75%. The scleractinian habitus showed that they were under attack by the sea star Acantaster planci, whose population density reached 5~7 ind/m².

Concurrently with A. planci the gastropod Charonia tritonis, the bivalves T. squamosa, and relatively young T. crocea occasionally occurred there. At a distance of 200~400 m from the beginning of the transect the settlements of Acropora were still spread, however, the settlements of A. formosa, A. cytherea, and A. hyacinthus were the most common there. Among Acropora settlements, more often than previously, bottom areas with dead corals and their fragments, which were more or less covered with the calcareous algae Amphizoa, Halimeda, and Hyphnea panosa occurred. With the 430th meter of the transect Acropora settlements acquired a distinctly patched pattern, and the percentage of projective cover of the bottom varied from 40 up to 80%. In that zone as a whole, concurrently with Acropora, individual colonies of Favia, Favites, Montipora, Porites and Heliopora were widespread. Starting from the 450th meter of transect, the extended buttress system area began at a depth of 10 m, comparable to that of the south reef area. It specified by the same set of growth forms and a similar species composition of corals and associated fauna. The zone was traced along the transect up to the 520th meter, then the number of corals and diversity of their growth forms decreased on the reef slope. Massive and encrusting forms dominated and occasional small bioherms occurred. The projective cover of the bottom did not exceed 12%~15%. A further increase in depth up to 14 m was associated with strong silting of the bottom and an increase in water turbidity. Only occasionally, after the 570th meter of transect, was it possible feel a small colony of coral by hand.

1.2 Reef of Ly Son island

Transect from the southwest to the northeast side of the reef (Figure 4). At a depth of 25 m, on the fore reef platform with slightly silted sand sediments with detached boulders and spalls of dead coral, isolated colonies of alcyonarian, gorgonarians and scleractinian occurred. A gradual decrease in depth observed to the northeast for 200 m of transects. The number of coral colonies significantly increased along with an increase in their size. Sinularia dura, Sarcophyton sp., Porites lobata, Isopora palifera, Pocillopora verrucosa, and Montipora venosa were the most common corals. The coral covering of the substrate did not exceed 5%~7%. At a depth of 12 m, bioherms from 0.9 up to 2.5 m high and up to 1.5~4 m in diameter were common. They consisted of polyspecies settlements of alcyonarian and scleractinian, in which Sinularia, Porites, Favia and Favites prevailed. The first dominated by substrate cover, up to 30%, the rest by number species up to 7~9. The scleractinian of the Euphyllidae, Meruliniidae, and Mussidae families (by 2~3 species) and individual colonies of Acropora, Montipora, Astreopora, Pocillopora, and Seriatopora occurred in that part of the reef rather often. Sponges, bivalves, gastropods and the sea urchin were characteristic in the associated invertebrate fauna for the area (see Table 2). Shrubs of the macrophytes Asparagopsis taxiformis, Padina australis, Caulerpa racemosa, Amphiroa fragilissima, and Halimeda sp. The composition of the fauna of reef slopes also had high degree of similarity, 78.9% of the species were in common. The slightly lesser similarity of the reef slope communities explained by the greater richness of macrophytes at the reef of Ly Son island.

Figure 4 Scheme of the cross-section profile of Ly Son island reef

The outer reef slope. This characterized by the presence of two morphologically differing parts, the lower and upper (Figure 5, nomenclature by Picard, 1967; Battistini et al., 1975). In the lower part (of the reef slope platform, at depths from 30 to 10 m) there were numerous alcyonarian and ahermatypic corals Balanophyllia, Dendrophyllia, and Tubastrea and hermatypic scleractinian were presented by stony and encrusting forms, Pachyseris, Leptoseris, Pectinia, Echinophyllia, Euphyllia, and Mycedium. The percentage of substrate covering by corals in that part of slope was rather low, 0.1%~5%. The upper part of the reef slope (buttress system, at a depth from 10 to 3 m) characterized by the presence of a system of channels, niches and spurs. Coral species diversity and substrate covering by corals (up to 40%) was higher there. Patches of monospecies settlements of the alcyonarian Sinularia or Lobophytum, of the scleractinian Acropora and Porites, and of Millepora and Heliopora occurred. In the lower areas of the upper part of the reef slope massive and encrusting forms of colonies of Goniopora, Goniastrea, Favia, Favites, Platygyra, Echinophyllia, Turbinaria, and Montipora prevailed. They replaced higher up by branching forms of colonies, primarily Acropora, and species that are able to inhabit an environment of intense hydrodynamics, viz., Acropora digitifera, A. humilis, Pocillopora verrucosa, Goniastrea retiformis, Millepora platyphylla, and Heliopora coerulea often occurred.

Figure 5 The outer reef slope at Ly Son island (depth 4 m)

Reef flat. Normally this was a vast zone with a continuous substrate cover of corals interrupted by sandy channels. This zone characterized by the development of dominant species of Acropora and Montipora and of branching forms of Porites (A. humilis, A. monticulosa, M. aequituberculata, M. porites, P. cylindrica, etc.). The significant role in the formation of the reef flat community belonged to the alga Chnoospora, Turbinaria, Asparagopsis, Hyphnea, Amphizoa, and Peissonelia. The projective cover of substrate by corals was 75%~100% as a rule.

The inner reef slope. Similarly to the outer slope it may be divided in two morphologically differing parts. The upper part of the slope distinguished by the high percentage of substrate covering by corals (not less than 75%~80%) and by greater species diversity. Patches of polyspecies settlement of corals alternated with monospecies settlement occupying greater areas of the bottom (Figure 4). Settlements of Sinularia, Acropora, Montipora and of branching forms of Porites dominated. In medium (transition) part of the inner slope species of the Pachysris and Merulina genera could dominate. The base of the slope was characterized by a lower percentage of substrate covered by corals (20%~40%), by the lack of extended monospecies settlements, and by the development of large "heads" of massive corals. It gradually transited into a sandy platform of lagoon separating reefs from the shore.

The surveyed reefs had a very distinct axial zonation. Their central part (the reef flat) characterized by a homogeneous coral community, where vast fields of branching and lamellar Acropora and Montipora pronouncedly dominated. At the southeast, south and, especially, west margin of the axial zone, the death of scleractinian observed. Scrap of colonies and entire dead colonies formed a zone of sediment accumulation in these reef areas. Finally, an extended zone of fragments, sand, and silt sediments formed in peripheral areas of the reef flat. All this implies that the reef flat community was close to the later phase of reef succession (Dollar, 1982; Sakai et al., 1986; Dai, 1993, 1996; Latypov, 1999) or, similarly to some reefs of the Indopacific (Pichon, 1974, 1981), was in a maturity or equilibrium stage of development. Diversity at first increased and then gradually decreased as more and more species became established. Monopolists are plate-like and branching Acropora. The decline in diversity in older flows was due to space limitation and competitive exclusion by dominant species (Glynn, 1976). The geomorphological characteristic: presence of fore reef, epi-reef, and back reef (Figure 1, 6) complexes with characteristic compositions of flora and fauna, and also obligatory presence of a lagoon separating the reef from fringing coast reefs, all enable us to attribute them to the barrier type of reef (Coris Glossary, http://coris.noaa.gov).

Figure 6 Bioherm on the reef Bath Long Vi (depth 10 m)

1.3 Reef of Bach Long Vi Island

Bach Long Vi Island extends for 1.6 km from northeast to southwest at the exit from the Gulf of Tonkin. It is surrounded by an adjoining reef with well-defined main physiographic zones (reef crest, reef flat, reef slope, etc.) and a small lagoon on its southwestern side. In common, (264) species of corals and accompanying macrobenthos identified on the investigated reef. Representatives of the Acroporidae, Poritidae, and Mussidae predominated among scleractinian. Single-species aggregations of alcyonarian Sinularia and Lobophyton and the hydroid Millepora were fairly numerous. Of the accompanying macrobenthos, the sea urchins Echinostrephus molaris, Diadema setosum and Echinothrix diadema, the starfishes Acantaster planci and Culcita novaeguineae, as well as the holothurian Holothuria atra occurred most frequently. The bivalves Lopha cristagalli and Pinctada margaritifera were almost ubiquitous. Asparagopsis taxiformis, Caulerpa racemosa, Turbinaria ornata, Padina australis, Sargassum olygocystum, and Gracilaria sp. predominated among the macrophytes.

At the beginning of transect, on the northeastern part of the reef, at a depth of 16 m is a fore reef platform or a fore reef. This is an area of slightly silty coarse and medium-grained sand with inclusions of blocks and fragments of dead coral. Sparse colonies of alcyonarian, gorgonians, and scleractinian encountered here. A gentle slope was observed stretching 250–300 m northwest. With decreasing depth, the number of large colonies of corals markedly increased. Soft corals Sinularia dura, Lobophytum sp., Sarcophyton sp., scleractinian Favites abdita, Isopora palifera, Montipora venosa, Porites lobata, and Goniopora stokesi predominated in terms of frequency. The coral covering of substrate was 5%~7%. The reef slope down to about 12 m depth covered with coral thickets and large bioherms up to 4~5 m high (Figure 6). This reef zone dominated by two to three species of Sinularia, Lobophytum, and Sarcophyton (Figure 7), massive colonies of Porites, plate-like and encrusting Montipora, Pectinia, Pachyseris, plate-like and digitate Acropora, and branching Pocillopora. The macrophytes Turbinaria, Asparagopsis and Gracilaria also encountered. The covering of substrate was up to 30%~40% for corals and 10%~20% for algae. Large colonies of Porites provided the basis for bioherms (Figure 8). Among other common inhabitants of the reef were the starfishes A. planci, C. novaeguineae, and L. laevigata, the sea urchin D. setosum, and mollusks P. margaritifera, Pteria penguin, Tridacna squamosa, Lambis lambis and Conus textile. With decreasing depth to 8~10 m, the number of corals increased and hence so did the coral cover up to 7%~10%. The most widespread on this part of the reef slope were S. dura, Acropora humilis, M. venosa, P. lobata, G. stokesi, Platygyra lamellina, Leptoria phrygya, Lobophyllia hemprichii, Merulina ampliata and the hydroid coral Millepora platyphylla (coral cover 40%~60%). Individual bushes of macrophytes P. australis, Turbinaria sp. and A. taxiformis, the sponge P. testudinaria, the starfish L. laevigata, the sea urchin E. diadema, and the holothurian H. atra were encountered.

Figure 7 Polyspecific settlement of various Alcyonarian on the reef Bath Long Vi (depth 10 m)

Figure 8 Bioherm on the reef Bath Long Vi (depth 6 m)

At a depth of 2~6 m, the upper reef slope with a well-defined system of spurs and grooves (buttress system) supports the highest species diversity of scleractinian (more than 150 species). A community of Acropora and Montipora occurred this depth. Acropora cytherea, A. hyacinthus, A. formosa, A. grandis, Montipora hispida, M. aequituberculata, M. vietnamensis, Pocillopora verrucosa and Seriatopora hystrix were dominant. As a rule, large colonies of Acropora millepora, A. specifera and M. hispida (or M. eaequituberculata) formed stacked aggregations that covered 100% of the substrate over several tens of square meters. In this zone, the calcareous algae Poroliton sp. and Halimeda sp., the alcyonarian Cladiella pachyclados, the scleractinian Acropora robusta, A. humilis, A. monticulosa, I. palifera, Pocillopora woodjonessi, S. hystrix and Galaxea astreata, various poritids and faviids (5~7 species of each), the hydroid M. platyphylla, macrophytes Turbinaria, Gracilaria and Asparagopsis were widespread. Along with them, the starfishes L. laevigata, C. novaeguineae, the sea urchins D. setosum, E. diadema, the holothurians H. atra, and the individual mollusks T. squamosa, Trochus maculatus, Cyprea arabica, and C. textile encountered.

At 2.5 m depth, a reef crest (breakwater) exists. This is a coralogenic-algal ridge 3~4 m wide, with individual colonies of scleractinian and alcyonarian and single bush of macrophytes. At a depth of 2 m, the reef crest gives way to a reef flat. A reefogenous plateau stretches for up to 1.5 km and is cut with longitudinal sand channels running from southwest to northeast. Throughout the reef flat zone, diverse scleractinian-alcyonarian or alcyonarian-scleractinian assemblages observed. In the former assemblages, Acropora cytherea, A. hyacinthus, A. florida, A. robusta, and Montipora verrucosa predominated in terms of substrate cover and frequency of occurrence; Alcyonaria, Lobophytum and Sarcophyton dominated in the latter. Everywhere on the reef flat, large colonies occurred as patches of a single species such as Acropora valenciennesi, A. cytherea, A. florida, A. spicifera, A. millepora, A. humilis, M. aequituberculata, M. danae, M. undata, P. lobata, Cyphastrea microphthalma, Lobophytum sarcophyloides, Sarcophyton glaucum and Sinularia flexibilis. At these sites, scleractinian and alcyonarian covered the substrate completely. Of the accompanying macrobenthos, the sea urchins E. molaris, D. setosum and E. diadema, starfishes L. laevigata, A. planci and C. novaeguineae, and the holothurian H. atra found most frequently.

The sand paving the bottom of channels and refuges under the corals was inhabited by fairly numerous (0.5~2.0 ind./m²) gastropods Terebra sp., T. maculatus, Turbo argyrostoma, Drupa ricinus and Vasum turbinellum, as well as the bivalves P. margaritifera and Cardita variegata. On the northwestern side of the reef crest, at a depth of 4~16 m, is an outer reef slope with a system of spurs and grooves. It extends for 250~750 m and characterized by a high species richness of the coral community. Acropora and Montipora formed an upper reef slope community with the predominance of A. cytherea, A. formosa, A. grandis, A. millepora, A. spicifera, M. hispida, M. aequituberculata, M. vietnamensis, P. verrucosa and S. hystrix. As a rule, these were large colonies of corals that entirely covered the substrate over tens of square meters (Figure 9). The highest species diversity of scleractinian (more than 160 species) was observed in the spurs and grooves zone. In addition to acroporids and pocilloporids, numerous faviids, euphyllids, poritids, mussids, and dendrophylliids (5~7 species of each family) were widespread here, as well as individual colonies of alcyonarian and single bushes of algae.

Figure 9 Colonies of corals covered the substrate over tens of square meters on the reef Bath Long Vi (depth 8 m)

The accompanying fauna on the northwestern part of the reef was comprised of the same set of species as in the corresponding zones on the northeastern reef side. However, a greater number of mollusks, holothurians, sea urchins, and other organisms found here.

With regard to its geomorphological profiles, coral species diversity and zonal distribution, the reef of Giang Bo, Ly Son island and Bach Long Vi Island are comparable to the ribbon reefs of the Great Barrier Reef in Australia (Veron and Hodgson, 1989) and to the barrier reefs of the Philippines (Pichon, 1977) and Indian Ocean (Picard, 1967; Pichon, 1974; Bouchon, 1981). Based on its geomorphological characteristic, the presence of a large elongate and wide reef flat with distinctive flora and fauna, as well as a small lagoon, the investigated reef can be classified accordingly as the barrier reefs and the platform reef type.

The Bach Long Vi reef exhibits a pronounced axial zoning. Its central part (reef flat) characterized by a homogenous coral community distinctly dominated by branching and plate-like Acropora and Montipora, which form extensive fields. The periphery of the reef plateau consists of an extensive zone of accumulation of debris from the remains of dead coral, sand, and silt. The reef community is approaching a maturity or equilibrium stage analogous to similar Indo-Pacific reefs (Dollar, 1982; Latypov and Malyutin, 1990; Dai, 1996; Latypov, 1990, 1999, 2000).

The high species diversity of the reef community of Bach Long Vi and its ecological status require special attention, and therefore recommendations were given to the Academy of Science and Technology of Vietnam regarding the establishment of a protected area on the Bach Long Vi reef for the purpose of conservation and restoration of the biodiversity of the Gulf of Tonkin as a whole.

2 Materials and Methods

The research of the composition and specifics of spatial distribution of corals and their associated fauna and flora was carried out on the same hydrobiological transects in three reefs in the South China Sea in 2004~2007 (Figure 10, 11). The traditional method for similar studies, consisting of the frames and transects described previously in detail (Loya and Slobodkin, 1971; Mergner, 1979; Latypov, 1995), was applied in the research. Substrate covering by corals and macrophytes was analyzed and the number of various forms of various coral colonies and domination of individual species were determined at each transect using SCUBA technique.

Figure 10 Schema location of the reef

Figure 11 Schema of the reef Bath Long Vi

Along the 100~200 meter's using frames, divided into 100 squares 10 cm², assessed the number of species branch, massive, incrusting and funnelform colonies of scleractinian and the degree of coverage of the substrate of corals and algae. Number mass a species of mollusks and echinoderms counted up on the area of 5~10 m². The number of colonies of corals recorded at transect, is calculated using the Shannon diversity index using the formula H' =ï¼Σ pi log Pi, where Pi is the prevalence of colonies giving genera (Bakus, 1990). The wide use of the underwater photo technique was a specific feature of this research. The population density of associated macrofauna was assessed from the projective area of the bottom (corals) taken for the count area. The reefs characterized based on cumulative data, not considering annual variations.

Acknowledgement

The author is sincerely grateful to Nikolai Selin (Institute of Marine Biology, Vladivostok) for help during field investigation of the reef. I am grateful to the anonymous reviewers for their valuable constructive comments to the manuscript of the article.

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International Journal of Marine Science

• Volume 3

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