by Yuri LATYPOV, Dr. Sc. (Biol.), manager of the Laboratory of Benthos Ecology of the RAS Far Eastern Branch Institute of Marine Biology

Surveys of ecosystems of tropical seas have been carried out in our institute since the day of its foundation at the Pacific Ocean shore in Vladivostok. We first visited cays more than 30 years ago and now have a complete idea of a great biological diversity of this unique community, its structure, problems of existence under the conditions of increasing anthropogenic pressure; besides, we realize how to preserve and keep it for the future. Our knowledge is proved by results of experiments carried out on the Mieu and Mun islands near Vietnam coast.

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According to the last data, there are 382 species of reef-building corals of 80 genera living near Vietnam coast. A third of them (133 of 26 genera) was described by scientists only at the end of the 20th-beginning of the 21st century, 12 species of 6 genera having been unknown to the scientists before that time. Such a diversity (which is possible for the reason of a high content of biogenic elements in comparatively shallow local waters) does not cause deposition of thick sediments on cays. But these cays, analogous to formations of the Indian Pacific region, which are well formed from the point of view of structure and morphology, are characterized by a bionomic zoning: heterotrophic organisms dominate the internal slopes, and autotrophic organisms, the outer slopes.

Cays of Indonesia, the Philippines, and the Great Barrier Reef of Australia are considered the faunistical center of origin of tropical corals, which is not by accident: about 360 - 410 species of scleractinia belonging to 70 genera live in this region of the south-western part of the Pacific Ocean (Dr. Charlie Veron from the Australian Institute of Marine Science, 1995; author of the present article, 2005). Maximal variety of these organisms is observed in a so-called "fertile" triangle; corners of the triangle are formed by the Philippines, Malacca Peninsula, and New Guinea. Vietnam shore is also likely to be assigned to this territory, for the degree of similarity of its species composition with that of Thailand is 76.4 percent, 72.3 percent for Indonesia and 81.6 percent for the Philippines (i.e. extremely high).

In a more spacious West Pacific triangle (with corners formed by cays of Vietnam, southern islands of Japan, and the Great Barrier Reef of Australia) scleractinic fauna is also rather homogeneous. Thus, about 75 percent of Japanese species are similar to those of Australian waters and are the same as 77.5 percent of Vietnamese ones, and the latter are similar to Australian ones (86 percent of uniformity).

Consequently, Vietnamese shore from the Gulf of Tonkin to the Gulf of Siam is an organic single whole from the biogeografical point of view and makes part of the Indian Polynesian province of the Indian Pacific Region.

THREAT OF REGIONAL SCALE

Abundance of fish, shrimps, crawfish, commercial shellfish, and algae in coastal waters to a great extent depends on the condition of cays. Like humid tropical forests, the reefs are the most productive natural ecosystem, where a complex habitat characterized by an extraordinary diversity of niches for all organisms is formed.

It should be noted that development of the travel industry connected with different types of active rest-breath-holding diving and snorkeling, amateur recreational and commercial fishing, glass boating, etc. - make cays an important element of the economy in a number of countries. According to experts, however, human activity becomes a threat on a local and sometimes regional scale to this ecosystem.

At the present time Vietnam with its large settlements in coastal areas is characterized by an economic upturn: housing and communicative construction boom, building of dozens of new hotels and diving complexes, expansion of sea farming. A large number of tourists are coming to see cays located near cities. But improvement of treatment facilities and environmental procedures lags behind noticeably-scientists are observing excessive

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ingress of terrigenous waste waters into the gulf, which is the main cause of aquatic contamination and damage of cays all over the world. The situation is getting worse in case of poor vegetation cover which is due to intensification of agricultural works, logging operations, mining, construction, waste water discharge, etc. As a result, cays lack light and are buried under a layer of sediments; friction processes cause abrasion of tissues of polyps - a list of negative consequences could be continued.

Waters enriched with organic substances influence metabolic processes in zooxanthellas (symbiotic microalgae that cays cannot live without), are conducive to the development of phytoplankton, which reduces the degree of illumination and contributes to the development of benthos filtration organisms. In such a context reef-building corals cede to macroalgae and other invertebrates in the struggle for nutrients.

MIEU AND MUN ISLANDS

In recent years research organizations of Vietnam with the assistance of the national government have been researching into the evolution of reef ecosystems, and are trying to find ways to preserve and reproduce them. Employees of our institute are also engaged in these works.

Mieu, Tarn, Mot, Che and Mun islands in the Nyachang Gulf are located at different distances from the shore, and, consequently, are suffering from different anthropogenic impacts. The first island is in a close proximity to the city and the port, the last one is the most distant one and considered a natural reserve. Because of these characteristics the two islands were chosen as subjects of research.

The first investigations using autonomous diving outfit at Mieu and Mun islands were carried out in 1981.

Scientists employed a well-known method of frames and transects: each reef was described by a level of substrate coverage with corals and macrophytes, by the number of different forms of colonies; the parties gathered a quantitative and qualitative collection of dominating species of coral bionts. Based on the availability or lack of geo-morphological zoning and characteristic sediments, the scientists defined structural (underwater elevation of this type with a pronounced zoning and reef sediments was described in the south-eastern part of the Mieu Island) and structureless reefs, covering the substrate with a thin crust and slightly changing its shape (located around the Mun Island, where in September-October 2003 and January 2005 repeated surveys were performed).

Nowadays the Mieu reef surrounded by sea farms and tourist complexes shows noticeable changes. First, the substrate, corals, and other elements of the macrobenthos on the slope have been greatly silted, surrounding waters are characterized by maximal level of sediments - 35.28 - 48.6 g/m a day. Second, biocenosis is transforming: the number and size of colonies of reef-building scleractinias is decreasing and the number of associated organisms, such as calcareous algae of Halimeda and Chnoospora species, increasing. Formerly dominating various species of branched acropores* (Acropora) and laminar montipores (Montipora) are to a great extent replaced by a monospecific community of thin branched montipores. The level of substrate coverage with corals (one of the principal characteristics of well-being of this community) hardly ever exceeds 30 - 45 percent.

* Representatives of the Acropora genus often form the basis of cay, and the Montipora genus organisms play a significant though not a leading part. They form colonies of different shapes: branched, laminar, etc. - Ed.

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Transparency of waters influences communities of corals. A - different reefs (islands are listed by distance from the shore); B - various zones of one reef (Mieu Island): a - lagoon, b - reeflet, c - cay slope, d - cay slope bed; e - prereef platform.

Starting from the middle of the cay slope, one can find colonies of Chnoosporct among corals and their branches. This species as well as Halimeda has spread to all zones, it intensively occupies the substrate and covers up to 60 - 75 percent of its surface. In the upper part of the slope and on the reeflet* there live strip- and spot-like colonies (with an area of 3 - 5 m ) of branched and laminar-branched montipores and porous organisms**, covering 55 - 60 percent of the substrate. The lagoon is still inhabited by separate colonies-massive and spherical communities of porous organisms (most common) and branched acropores (rare). Substrate coverage level does not exceed 3 - 5 percent.

Changes also affected associated macrobenthos. About 20 - 25 years ago there occurred numerous diadem sea urchins (no less than 5 animals/m²), edible (1 - 2 organisms/m") and black holothurias, Linkia, Culcita and crowns of thorns starfish (Acantaster planci, 0.1 - 0.2 organisms /m²), shell-fish Atrina (up to 0.2 organisms /m²), Tridacna (0.5 organisms /m²), 3 species of gastropods, different cowries (0.2 - 0.5 organisms /m²), and other invertebrates. In 2003 - 2005 we could observe only separate atrinas, rare diadems and holothurias; on the contrary, crown of thorns starfish became rather common.

In the course of studies of the most distant reefs near the southern part of the Mun Island carried out in October 2003 and January 2005 we did not detect any substantial changes in the composition and structure of the community under consideration. But the level of substance coverage with live corals has decreased a little due to bleach and death of their separate parts or whole colonies of different species and some single organisms. Nevertheless, the diversity of species, especially at a depth of more than 5 m (where impact of divers is not so adverse) is still rather high.

* Reeflet - part of a cay, more or less flat lime platform, spreading from its outer slope to the shore. - Auth.

** Porous organism-one of the reef-building corals. - Auth.

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For half an hour of visual observations I spotted 108 species belonging to 40 genera of scleractinias. On this part of the cay there live no less than 10 species of acropores, which speaks for satisfactory existence conditions. There are also communities of the so-called mushroom-shaped coral fungi (up to 45 plants/m2) that are in the form of strips (there is a solid covering of the substrate inside them) perpendicular to the shore line. Besides, we saw a great number of young fungi once again attached to the substance. Probably, we observed the late stage of succession* in the researched area, when communities of corals of one species could form on a vast territory.

FROM DIAGNOSIS TO TREATMENT

Different levels of changes of coral communities of cays of the Mieu and Mun islands show differentiated anthropogenic impact. In the first case proximity to the city and Nyachang port has adverse effect. In the second case remoteness, location in a conservation area and under-population contribute to preservation of the ecosystem. That is why transparency of water near Mieu Island and water exchange ratio over the studied communities is less by 1.48 than that near the Mun Island, and daily sediments deposition level is higher by 1.3. Water eutrophication process is intensifying, which causes silting of the substance, decrease in its coral coverage, abundant macrovegetation, decrease in variety of reef-building organisms and associated macrobenthos dominants.

Alas, cays of the Mun Island, as well as in other regions of the world, are undergoing changes-first of all, we speak about bleach and death of some species of corals. But on the whole, we observe common succession processes typical of such communities: their composition and structure stay the same, while new communities of fungi appear, including young fungi growing from sinking coral slugs.

Dozens of scientific works are dedicated to the analysis of changes of coral communities under the influence of physical and biological factors; authors declare: the condition of cays is getting worse all over the world. That is why it is so important to know what we want to preserve-the diversity of corals on a separate cay, its fishery resources, or ecosystem as a whole. We should remember that changes can take a place on a level of a separate sample, population, ecosystem, and landscape. And the effects are short-term or long-term; short-term influences sometimes "shade" long-term effects. Only continuous monitoring, which takes into consideration all natural and anthropogenic factors, will enable us to assess stability of cay communities, determine tendencies and causes of current changes.

At the present moment a third of coral reefs on the planet is in a critical state, and only 40 percent are considered stable notwithstanding their proximity to human settlements. That is why the public and scientists of many countries are concerned about the problem of preservation and renewal of these natural resources and take different measures to solve it both on international and regional levels.

Corals are clonogenic organisms able to reproduce asexually. In so doing, as all Coelenterates, they can reproduce damaged parts of the organism, moreover-regenerate rejected or damaged fragments of colonies

* Succession - successive replacement of one type of biocenoses by another one in a particular area. - Ed.

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Survival ratio of transplants of different species of the Acropora genus corals (in percentage of total number of organisms used in the experiment).

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with a complete regeneration of original forms and characteristics. The history of formation of reef communities of the Ordovician and Silurian periods (more than 400 mln years ago) brings us examples of such a "regeneration" (described, in particular, by Boris Preobrazhensky, of the RAS Far Eastern Branch Institute of Geography, and by the author of the present article in 1980).

In publications dedicated to transplantation and cultivation of corals there have been considered various methodological, physical and biological aspects of the problem. The majority of specialists are inclined to believe that special attention should be given to sizes of fragments, their transplantation seasons, orientation in the place of transplantation and against the substrate, which is of high importance for the revival of reproductive performance of "recoverable" colonies. But before such an intervention into the cay ecosystem is undertaken, it is necessary to assess all critical aspects of a chosen method. It is essential to experimentally define procedures enabling us to get the maximum effect with the minimal number of used live colonies.

While performing surveys, we paid the main attention to the study of the role of species belonging for Acropora and Pontes species of corals in the process of transplantation of fragments of their colonies.

TRANSPLANTATION

In our work we used a series of species of scleractinias, essential for reef communities of the Indian and Pacific oceans, including Vietnamese Region: 8 species of acropores and 2 species of porous organisms. Surveys were carried out on the slope of the Mun Island cay in the Nyachang Gulf. The test facilities were set far away from open sea waters to avoid their influence: this area is protected from high waves by the mountainous relief from the south and a large Che island from the north. The availability of a natural reef at a depth of more than 12 m confirms the fact that there is enough light for coralliferous organisms. We examined the effect of four factors influencing norms of persistence and growth rate of corals: sizes of their fragments, species, attachment orientation, transplantation season.

Fragments of coral (1 - 3 branches of four of them belonging to different species were intentionally cut off by pincers) were fixed on a frame vertically, horizontally, and with growing distal* ends down. Corals were mounted on horizontal bars only to avoid attacks of predatory shellfish gastropods. Transplantation areas were located 20 - 50 m above donor colonies, at a depth of 6 - 7 m. Frames were raised 30 - 40 cm above the bottom to prevent covering with sediments of the "patients".

All surviving fragments regenerated (damaged ones including) and produced new branches; in 6 - 8 months about 60 percent formed basal attachments on horizontal bars of test facilities using them as substrate. Three transplants belonging to different species of Acroporadied: one of them attached itself to a metal frame by more than 75 percent of its length, two others could be damaged by Brachiopoda, Drupela rugosa (from one successfully regenerated branch of Acropora scientists took off two shells of the above-mentioned shellfish).

* Distal end of a coral fragment is the farthest one from the middle plane of the body or from the basic organ of the appropriate system. - Auth.

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In general, the persistence norm of fragments made up 60 - 100 percent and depended on their size, species and duration of the experiment, but was hardly determined by their orientation and transplantation seasons. In 2 - 2.5 months after the "operation" on the surface of all surviving species of corals (including lower part damaged after cutting off from donor colonies) there were formed new branches. In the course of 12 - 18 months corals of different species gave from 3 to 60 branches; the biggest number of branches grew on the largest fragments of ascopore* elsea and cylindrical porous organism-71 and 60, respectively. It is necessary to emphasize that the average monthly growth rate of new and buildup of donor big transplants pricked out in spring was 1.2 - 1.37 times higher than that transplanted in autumn.

Linear growth of fragments was 70 - 160 mm depending on their size, species and season of "operation". Large fragments grew up 1.3 - 1.5 times faster than middle-sized organisms and corals of the same species - Acropora and Pontes. A year and a half old transplants grew 1.2 - 1.4 times bigger than the year-old corals.

The results of the experiment with test facilities elevated over the bottom in natural conditions of the reef slope prove the efficiency of the offered technology of transplantation of fragments of arborescent colonies. Colonies characterized by a powerful initial branching formed more new branches located the same way as in donor colonies. They had a larger area of living tissue of polyps per total length unit. Besides, their capacity to receive power through photosynthesis or via capture of nutritive particles is potentially higher that that of small fragments. Rather high rates of growth of transplants of all species are likely due to their movement into a new, well-illuminated and uncrowded environment. The fact that we raised the frame 30 - 40 cm above the silty bottom also played a significant role: sediments often restrict the growth of corals or even cause their death; in our case the probability of such an outcome decreased.

To sum up, I would like to say: the success of growing fragments of corals in a natural reef environment depends on different factors, the species and size being dominant ones. Good lighting and minor presence of competitive macrobenthos promote the process. Our experience makes it possible to produce a great number of acropores and poritids within rational time limits over a certain reef area.

I would like to emphasize that the results of the experiment could be used not only to reproduce natural coral communities, but also to grow separate organisms and colonies, which will enable us to satisfy the needs of collectors, and reduce the risk of negative influence on natural cays. Development of modern technologies, creation of a wide net of reserves and national parks, and artificial reefs will help to keep and regenerate the biological diversity in these unique ecosystems. They will be useful to all future generations.

Illustrations provided by the author

* Ascopore is a genus of reef-building corals. - Auth.