American Journal of Climate Change, 2013, 2, 284-291 Published Online December 2013 (http://www.scirp.org/journal/ajcc) http://dx.doi.org/10.4236/ajcc.2013.24028 The Composition and Structure of Reef Community at Tho Chu Island (South China Sea) after Ketsana Typhoon Yuri Ya. Latypov A.V. Zhirmunsky Institute of Marine Biology, Far East Branch of Russian Academy of Sciences (FEB RAS), Vladivostok, Russia Email: [email protected] Received August 5, 2013; revised September 7, 2013; accepted October 5, 2013 Copyright © 2013 Yuri Ya. Latypov. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT Fringing the reefs of the island Tho Chu explored a quarter century later now reexamined in the Gulf of Thailand of the South China Sea. It was found that most of the reefs of the island were lost after the passage of typhoon “Ketsana” ac- companied by heavy rains and strong sea waves higher than 2 meters in October 2009. Because of these natural phe- nomena, physical destruction of many of the coral communities occurred. Removal of terrigenous sediments from the islands in the water has led to increased sedimentation and loss of almost all the scleractinian family Acroporidae, the main building corals on the reefs of the Indo-Pacific, at present, in places where once there was full-reef community succession restoring the reef due to the survivors of the typhoon colonies of coral genera Pocillopora and Acropora. Keywords: Typhoon Ketsana; Destruction; Reef Community; Change; Succession; Vietnam 1. Introduction prone to intense excitement even during strong winds. In times of typhoons, such excitement leads to severe physi- Coral reefs are under threat worldwide. An estimated cal damage and destroying fragile coral colonies falling 58% of reefs are classified as threatened [1], and 11% of asleep and their bottom sediments. This peculiarity of the the original extent of coral reefs have already been lost [2]. The composition of remaining coral reefs is also coastal geomorphology and hydrology of the region af- changing rapidly. For example, coral cover on reefs fects the formation of his few reefs, which are also often across the Caribbean has decreased by 80% in the past subject to strong typhoons. So in October 2009, the Viet- three decades [3], and some formerly abundant coral nam landfall of typhoon “Ketsana”, which reached gusts species have almost disappeared from the region [4]. The of wind up to 165 km/h corresponded to category 2 on a causes of coral decline are thought to include a combina- scale Saffir-Simpson Hurricane. Typhoon was accompa- tion of direct anthropogenic factors, such as overfishing, nied by heavy rainfall (about 200 mm of rain), and the pollution, and sedimentation [5]. Hurricanes and tropical excitement of the sea more than two meters tall. After storms are perhaps the most obvious and frequent natural comparable in strength typhoon corals are destroyed at disturbances affecting reef communities. They have long depths greater than 12 m—60% to 80%—between 12 m been recognized as being important determinants of both and 30 m and 100%—beyond 35 m, where as earlier liv- the structure and function [6-8] of reef ecosystems. A num- ing coral cover age ranged from 60 to 75% in these zones ber of studies have documented the severe immediate con- [11]. As is well known, flows of storm (flash flood) of sequences of hurricane impacts at single sites in terms of wastewater and desalination are characterized by strong reduced coral cover [9,10], highlighting the effects as being turbidity due to the large number of different particulate impressive in magnitude, speed, and patchiness. matter, which have a detrimental effect on the existence of Vietnamese island of the Gulf of Thailand for the most coral communities, leading to their partial and sometimes part is open all year co wind waves in all directions. total loss [12,13]. Most of the reefs of the island Tho Chu Their slopes are formed by underwater boulders and boul- were virtually destroyed. When the coastal zone at depth of der heaps of moving from deep stony deposits, and on to the 5.3 m, 40% of its corals were destroyed; at depth of 5 - 8 m platform of sand and silt. Openness and vulnerability of in the settlement of Acropora—100%; at depth of 8 - 12 m islands, shallow water of the coastal zone make them —60%; 5.3 m, 40% of its corals were destroyed; at depth of Open Access AJCC YU. YA. LATYPOV 285 5 - 8 m in the settlement of Acropora—100%; at depth of 8 - The re-examination reefs in 2010 and 2013 on the 12 m—60%; at depth of 12 m—10%. In this regard, it is same cuts as in the 80 s of the last century have been appropriate to go back briefly to the information about found significant changes in the composition and struc- the state of these reefs of quarter century ago. ture of reef communities. Therefore, these results of the First reefs in this region have been studied in detail in studied reefs in the region, in our view, are interesting, the joint Soviet-Vietnamese expeditions in 1986 and and as an independent study, they can also be used as 2007, and then World Wildlife Fund (WWF) in 1992- material for comparison with the changes taking place on 1993 [14-17]. There are clarified species composition, the reefs not only in the central and southern Vietnam, population density of dominant species of macrobenthos but also throughout the entire Pacific. and the degree of coverage of the substrate corals and macrophytes. Through identifying these reefs based on 2. Materials and Methods the data points of the coral community, it shows that the Using SCUBA equipment, we investigated the composi- reefs are quite satisfactory and similar with those of tion, distribution of scleractinian corals and mass species North and South Vietnam and the Indo-Pacific [18-21]. of macrobenthos, structure of communities in reef zones Tho Chu Island (9˚18'N, 103˚28'E), together with sur- at four sections in sandy and stony inlets and near rocky rounding rocks and small islets is about 11 km in diame- coasts (Figure 1). Investigations were carried out in ac- ter (Figure 1). The relief of the island represents a high cordance with the standard hydrobiological technique plateau bordered by steep abrasion denudation slopes. It is using quadrats and transects [22,23]. Abundance of mass a remnant of a large sub platform structure destroyed in species of mollusks and echinoderms, branched, massive, the Pleistocene because of a tectonic immersion of the encrusted and funnel-shaped scleractinian colonies, as well bottom in the Gulf of Siam. The island consists of coarse as the degree of substrate cover by corals were estimated layered sub horizontal sandstones and conglomerates of along a 150 m transect frame divided into 100 squares coastal-marine genesis, which is evidenced by well-rolled with the area of 10 cm2 each. Photographing of reef land- gravels, shoestring distribution of pebbles, and the pat- scapes, and their flora and fauna was conducted. More tern of rhythmic and textured sediments that is character- than 750 photos by Olympus and Lumix digital cameras istic of coastal shallows. The development of the ruined- were made for later analysis of species composition [24, rocky submarine relief is, to a significant degree, due to 25] and structure of community of coral reef survey me- these geomorphologic peculiarities. The submarine slopes thods [26-28]. Coefficients of species diversity corals represent boulder-block bottoms transforming in deeper were calculated by the formula: depths into stony and gravel deposits, which, in deeper H =l ni N xn ni N , where H—Shannon Di- depths, replaced by sandy-corallogenic deposits with great versity Index, ni—number of individuals belonging to i amounts of organic detritus. The northern and northeastern species, N—total number of individuals [29]. slopes have ratios of 0.05 - 0.08 going down to a platform at a depth of 35 - 40 m. In the south and southeast, the slope ratio is 0.032 - 0.044 and the slope transforms into the plat- 3. Results and Discussion form at a depth of 23 - 25 m. An ingressive sandy bay with In 1986, the diversity of species on different reefs varied a slope ratio of 0.026 and a wide zone of wave accumula- from 335 to 387 species, of which 275 species in total tion in the innermost part is set into the western coast. were scleractinian. Ubiquitous and often dominated by 37 species: sponge Petrozia testudinaria; corals Sarco- phyton trocheliophorum, Sinularia dura, Lobophytum pauciflorum, Junceella fragilis, Seriatopora hystrix, Pocil- lopora damicornis, Acropora nobilis, A. cytherea, Pavo- na decussata, Pachyseris rugosa, Diaseris distorta, Pol- yphyllia talpina, Galaxea fascicularis, Lobophyllia hem- prichii, L. hattai, Goniopora stokesi, Platygyr daedalea, Diploastrea helioporaи Millepora platyphylla; mollusks Cyprea tigris, Beguina semiorbiculata и Malleus malleus; echinoderms Holothuria atra, H. edulis, Stichopus varie- gatus, Bohadshia graeffei, Diadema setosum, Echinotrix diadema, Culcita novaeguineae и Linckia laevigata; poly- chaetes Spirobranchus giganteus; and algae Turbinaria ornata, Padina australis, Laurencia papilosa, Caulerpa Figure 1. Schematized map showing the location of Tho racemosaи Sargassum duplicatum. Chu Island (a) and the position of transects 1-4 (b). Distribution of certain dominant species or groups of Open Access AJCC 286 YU. YA. LATYPOV the same species in different zone of the same reefs re- and 20 spec./m2 respectively). Besides the dominating vealed several macrobenthos of communities. The com- species, constant components of this community are other position and characteristics of formation of which are species:corals Verrucella umbraculum, S.