Effect of artificial disturbance on coral reef communities : A case study in the Gulf of Thailand

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Community structure of the coral reefs in the innermost part of the Gulf of Thailand was analyzed and the results were compared with those collected by our previous expeditions in 1884 and 1987 in order to make clear the effect of anthropogenic disturbance. No marked changes were found in the structure of coral community on hard bottom, but several solitary coral species which had been very abundant on the soft bottom before were observed to disappear. A large number of dead oyster shells were seen around the area where accumulation of sandy particles was conspicuous on the lower intertidal. On a sandy beach, disappearance of the sandy particles was found. These phenomena seemed to be results of some human activities.River water brought huge amount of suspended materials and low salinity effect was also conspicuous. Coral reef communities were covered with <25 of salinity at low tides in the rainy season, while with normal sea water at high tides.Effect of low salinity sea water and suspended materials, of which sources were not only river water but also areas of the construction of a harbor etc.nearby, on biological activities such as filtration by suspension feeders and sediment removal by corals was quantitatively estimated.Toxic materials accumulated in sponges, tunicates or other invertebrates were analyzed in the areas affected by human activities and clear waters. Species composition of these species was different in these areas and effect of toxic materials on coral community structure was discussed.Low salinity water containing much suspension was considered to control the community and it was also speculated that increase of suspended materials and change in current pattern caused by some anthropogenic activities affected its structure.