Zonation of Unstructured Coral Reef in Various Region of Indo-Pacific  

Yuri Yakovlevich Latypov
A.V. Zhirmunsky Institute of Marine Biology, Far East Branch of Russian Academy of Sciences (FEB RAS), Vladivostok, Russia
Author    Correspondence author
International Journal of Marine Science, 2014, Vol. 4, No. 39   doi: 10.5376/ijms.2014.04.0039
Received: 29 May, 2014    Accepted: 30 Jun., 2014    Published: 28 Jul., 2014
© 2014 BioPublisher Publishing Platform
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.

Zonal structure and composition of coral communities of so-called “unstructured reefs” were analyzed in various reefs of Socotra Island and Vietnam. Those unstructured reefs located on the periphery of the Indian Ocean, the high eutrophication waters of Gulf of Tonkin, and South China Sea. Scheme assumed succession of reefs formed structural morphological zonation (lagoon, reef flat, etc.). Unstructured reefs represent a stable ecosystem adapted to strongly turbid and eutrophic waters. The reefs have stable species composition and community structure in the same bionomical zones on different reefs, and are characterized by high species diversity. The composition and distribution of coral communities on encrusting reefs, forming heterotrophic internal and autotrophic external components of an integral ecosystem do not differ from such on reefs in terms of a clear pattern of zonation in general throughout the Indo-Pacific. 

Unstructured reef; Structure; Species composition; Indo-pacific

The two main variables determining the geo- morphology, or shape, of coral reefs are the nature of the underlying substrate on which they rest, and the history of the change in sea level relative to that substrate.
In Darwin’s theory sets out a sequence of three stages in atoll formation. It starts with a fringing reef forming around an extinct volcanic island as the island and ocean floor subsides. As the subsidence continues, the fringing reef becomes a barrier reef, and ultimately an atoll reef (Darwin, 1842). The three principal reef types are: Fringing reef – directly attached to a shore, or borders it with an intervening shallow channel or lagoon; Barrier reef – reef separated from a mainland or island shore by a deep channel or lagoon; Atoll reef– more or less circular or continuous barrier reef extends all the way around a lagoon without a central island. In addition, there are still other concepts and terms to refer to different types of reef: Patch reef, Apron reef, Ribbon reef and so on (Coris glossary, internet).
The mass development of corals either in models of coral community succession (Connell and Slatyer, 1977),  on the other hand, in the formation of reefs on artificial substrata (Schuhmacher,  1977) and in reefs at different stages of development (Hubbard, 1974; Loya, 1976) must follow a phased formation of a cover by biogenic deposits in which corals are pioneer settlers. Colonies of certain species settle and gradually give rise to multispecific settlements (Hubbard, 1974) that form, with time, the primary coral layer (Pichon, 1974; Dai, 1993).
In areas with monsoon climate, there are structural and unstructured reefs (Wainwright, 1965; Latypov, 1995). Their development is associated with a constant turbidity, periodic dilution by fresh water. Their limestone framework is at the stage of “framework building” (Sheppard, 1982) when cementation of sediments and the filling of reefogenous deposits occur. It is rather difficult to distinguish such reefs from real structural reefs or the different developmental stages of reef like “coral layers” and “specialized settlements” and may need a new term. Such encrusting reefs, along with the usual structural reefs, are widespread along the shores of Vietnam (Sheppard, 1982; Latypov, 2013; Latypov and Malyutin, 1990).
In the outlying areas of the Indian Ocean and in high eutrophication waters of the South China Sea met frequently the so-called "unstructured reefs", who did not have the typical reef zonation in morphological terms. However, the composition and structure of coral communities largely corresponded to the classic reefs. Brief description and analysis of these reefs is dedicated to this article.
1 Methods and Material
1.1 Sampling site
Using SCUBA equipment were studied the species composition and distribution of scleractinian and mass species of macrobenthos (a little more than 400 species), structure of communities in every zone of reefs at  islands Socotra (Indian Ocean)and some islands of Baitylong archipelago (South China Sea, Figure 1).


Figure 1 Schematic section of reef. A) profile and zonation; I-IV) bionomical zones, a) facies A. microphthalma and S. pistillata, b) facies L. phrygia and P. lutea, c) facies L. phrygia and S. trocheliophorum, d) facies P. abdita and P. camersoni; Arabic numerals along the abscissa - number of species of scleractinian in the zone, B) degree of corals covering the substrate (1) and ratio of branching (2), mass colonies (3); along the abscissa is distance from beach, m; along the ordinate is degree of covering of substrate, %, number of colonies.


1.2 Transected method Surveys have been done according using frames and transects method (Loya and Slobodkin, 1971). Two hundred meters transects with the foot age marking were mounted in the open and closed bays, on the headlands, near rocky, stony and sandy shores in order to maximally cover the diversity of reef communities in the region of survey. Along the transects, on every square meter the quantity of branchy, massive, incrusting and funnel-form colonies of scleractinian, degree of substrate covering with corals in the form of a frame divided into 100 squares, and the quantity of mass species of mollusks and echinoderms were accounted.
1.3 Identification of corals(228) species was made for analysis of species composition and structure of community of coral reef survey methods (Veron and Smith, 2004; Latypov, 2006a; Weinberg, 1981).
2 Results
2.1 Reef of Socotra Island
Coral reefs of Socotra Island do not have the usual reef zonation. The corals cover the substrate the low crust almost without changing his profile (Figure 2). There are the first zone consists of algae and coral with spots of eel-grass and corals. The zone is 20-60 m wide. The second zone is a steep section of the bottom with small boulders of insular rock and projections of beach rock between which there are accumulations of coarse-grained sand, organogenic detritus, and fragments of corals. The settlements are individual, polyspecific, with spots of large branching colonies of no particular species. This zone is 40-50 m wide. The third zone is also steep, with a hardly noticeable sloping section of sandy bottom periodically covered with fragments of dead coral. The settlements of scleractinian are dense and the large colonies are several meters in diameter and height. Bioherms and settlements of soft corals are broadly developed in this zone, which is up to 100 m in width. The fourth zone has an even sandy bottom, with numerous remains of dead corals on which colonies of scleractinian, alcyonarian, and algae, have settled. The soft corals frequently form dense polyspecific settlements.



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The morphological peculiarities, structure, composition, and distribution of corals make it possible to separate the following zones on reefs of Socotra Island (Figure 3).



 Figure 3 The appearance of bioherm, depth 6 m


Alga-Coral zone (I). Zone of distinct domination by algae Galaxaura spp. among which different colonies of scleractinian are distributed, notably massive and crusted forms of growth. These algae form spotted settlements, which cover the surface substrate by about 40%. The degree of coral coverings does not exceed 1-3%. The most common are scleractinian Psammocora profundacella, Stylophora pistillata, and Leptastrea purpurea. In general, habit, assembly of taxon’s, and growth forms of corals, the zone is comparable with the boat channel zone (Bouchon, 1981). It is 20-60 m wide from the lower horizon of the littoral to a depth of 2 m.
Zone of Coral Dominants (II). This is a zone of development of monospecific settlements of scleractinian appearing as alternating spots of proliferating branched, mass, and other colonies. The two species, S. pistillata and Acropora microphthalma, form the settlements. Algae Pocokiela variegata and the calcareous. Corallinacea are the most distributed among the macrophytes. The degree of covering by corals is 20-30% on the whole, and up to 80% in spots of settlements. The zone does not exceed 50 m in width, and depth is 2-5 m. This zone is comparable with the outer part of a fringed reef (Pichon, 1977; Bouchon, 1981; Latypov, 2013).
Zone of Bioherms (III). A characteristic feature of this zone is the development of polyspecific settlements, chiefly massive and massive crusted forms. Faviidae, among which very robust colonies of Leptoria phrygia and Porites lutea are separated, predominate. The zone is distinguished by a high specific diversity of scleractinian and alcyonarian. The degree of covering by corals is 30-40%. It is up to 100 m wide and 5-7 m deep and is comparable to the zone of crests and canals of the upper part of the outer slope of Indo-Pacific reefs.
Alcyonaria - Algae Zone (IV). A zone of spotted polyspecific settlements of soft corals among which different colonies of scleractinian and small sections of the algae Padina camersoni are distributed. Depletion and change in the taxonomic composition of scleractinian are characteristic for this zone. There are nearly no Acropora here, but Turbinaria, Goniopora, and Alveopora are common. The degree of covering dose not exceeds several percent’s. This zone is comparable to the lower part of the reef slope.
2.2 Reefs of Baitylong archipelago
Different islands at Baitylong archipelago, their sides and bays have various morphological profiles and patterns of reef zonation. Small islands and their bays have structureless coral reefs built by settlement of individuals or groups of colonies, rarely by bioherms (Figure 3, 4). Reef deposits form only a veneer; they do not form the reef framework and match the natural profile of the bottom which consists, for the most part, of large pieces of rock rubble and, rarely, of dead coral fragments. The morphology of such reefs is affected strongly by the underlying topography and only a reef slope is distinct.



 Figure 4 Different stages of development of a coral reef. A, superficial layer of corals on a solid substratum. B, Primary framework stage. C, Young fringing reef with formative zonation. D, Structural reef with clear zonation. (a, lagoon; b, reef flat; c, reef slope (by Latypov, 1995)


Coral community characteristics
Along the coast, for a distance of 20-40 m and at a depth to 1 m, occurs an algal-coral zone dominated by macrophytes i.e., Sargassum, Padina, Asparagopsis and Turbinaria, crusts of the zoanthid Palythoa and individual small massive and encrusting colonies of the scleractinian Porites, Leptoria, Goniastrea, Pavona and Hydnophora. The substratum covered with algae for no more than 10% (rarely 40% in some areas) with Sargassum polycystum or Asparagopsis taxiformis dominant. Corals cover between 7-15% of the substratum with Galaxea fascicularis, Leptastrea transversa and Porites lobata dominant, the latter forming flat microatolls up to 1.5 m across. At 40-60 m off the coast and with increasing depth to 2 m, the numbers and abundance of scleractinian increase. The degree of substratum covered with corals reaches 40% with P. lobata, G. fascicularis and Pavona decussata dominant.
Between 70-80 m offshore, the bottom drops from three to 9-11 m. The depth change occurs either gradually or by two to three sharp steps. An associated change takes place in species composition and pattern of coral settlement on the reef slope. Large (up to 2 m across) colonies of Galaxea, Lobophyllia, plate-like Acropora, Montipora, and plate-like encrusting Echinopora, Echinophyllia, Mycedium, Pachyseris and the lamellar-funnel form of Turbinaria are dominant. Massive colonies of Porites occur on the upper and middle parts of the reef slope (1.5-2 m in height). Species richness increases two fold. The degree of coral covers in creases to between 70-80% and to 100% in places with large colonies of G. fascicularis, Acropora cytherea and Lobophyllia hemprichii. The reef slope community is divided distinctly into two facies, i.e., Acropora cytherea + Galaxea fascicularis on the upper part of the reef slope and Cladiella sp.+Lobophyllia hemprichii on the lower. Towards the base of the reef slope (to a depth of between 8-10 m) scleractinian richness and individual numbers decreased. The genera Goniopora, Lobophyllia, Podobacia, Echinopora, Oxypora, Pectinia and Turbinaria, were most common here as individual colonies covering between 3-5% of the substratum surface.
3 Discussion
Zonal morphological differences, the specificity of species composition of scleractinian, and the coral structures of Socotra Island and most of the reefs of the Baitylong archipelago do not have zones typical for reefs of other Indo-Pacific regions such as lagoons, reef flat, etc. At many the investigated profiles, polyspecific specialized settlements, notably the common crusted forms, are developed. Colonies of S. pistillata, one of the pioneer settlements of reefs, universally distributed in relatively large numbers. Coral settlements represented in the form of a weak covering layer only slightly changing the morphology of the underwater slope (Hubbard, 1974; Dai, 1993; Latypov, 1995; Kosmynin et al., 1982; Latypov, 2003, 2011). The carbonaceous body of the possible future reef starts to form in zone of bioherms where large colonies grouped with bioherms. All this indicates that the coral structures of Socotra Island are in the middle stage of development of the contiguous reefs usually forming on the sloping substrate (Dai, 1993; Latypov, 1995).The present reef structures of Socotra Island and Baitylong archipelago may represent the foundation for the development of reefs with typical zonation. Under certain circumstances, the active growth of monospecific settlements of the second zone may promote the establishment of a porous skeleton, which is necessary for the formation of the structure of the real reef.
When such a reef crust is formed, more species settle and the primary framework of the reef grow vertically to the intertidal level (Figure 4). A porous framework of cemented benthic organisms is formed, which are mostly dead. A young fringing reef forms with a reef flat adjacent or almost adjacent to the shore (Latypov, 1987; Dai, 1993). In time and in the course of erosive and sedimentation processes, there is a transfer of deposits from the deep zones to shallower one sand vice versa. The areas of 'living' and 'dead' reef extend, reef deposits grow thicker and morphological zonation develops (Figure 4 C, D).
4 Conclusions
4.1 Features of reefs
Unstructured reefs of the Baitylong archipelago and Socotra Island represent a stable ecosystem adapted to strongly turbid and eutrophic waters. The reefs have stable species composition and community structure in the same bionomical zones on different reefs. The reefs are characterized by high species diversity (more than a third of all Pacific scleractinian species, (Latypov, 1987, 2003, 2011). Their limestone framework is at the stage of “framework building” (Wainwright, 1965) when cementation of sediments and the filling of reefogenous deposits occur. It is rather difficult to distinguish such reefs from real structural reefs or the different developmental stages of reef like “coral layers” and “specialized settlements” and may need a new term. Such encrusting reefs, along with the usual structural reefs, are widespread along the shores of Vietnam (Pichon, 1977; Latypov, 1995, 2009, 2013; Latypov and Malyutin, 1990).
4.2 The role of reefs in the reef ecosystem of Indo-Pacific.
Their development is associated with a monsoon climate, constant turbidity, periodic dilution by fresh water and, hence, the periodic destruction of a large number of corals. These encrusting reefs form on rocky and rubble boulder substrata or in turbid conditions and are known from other regions (Zhuang et al., 1983, Latypov, 1986; Trible and Randall, 1986). Unfavorable conditions are, overall, less continuous than favorable ones and reefs can, therefore, recover and survive (Latypov, 2003, 2006). The composition and distribution of coral communities on encrusting reefs, forming heterotrophic internal and autotrophic external components of an integral ecosystem (Sorokin, 1990) do not differ from such on reefs in terms of a clear pattern of zonation in general throughout the Indo-Pacific (Sorokin, 1990; Latypov, 2003, 2009, 2011).
The author thanks Irina Barsegova for her help in the preparation of the English text of this paper.
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