MICROGASTROPOD TROPHIC STRUCTURE OF YONGSHU REEF, SCS SINCE THE LATEST PLEISTOCENE WITH BEARING ON PALEOENVIRONMENT

Yongshu reef, South China Sea has been important subject for research on Quaternary paleoceanography of South China Sea in the last ten years. Reported here are microgastropods since late Pleistocene according to core1 of Yongshu reef. Research shows that there were four microgastropod communities, known respectively as mcirogastropod community of recent inner reef flat facies, that of lagoon slope facies, that of beach facies and that of inner reef flat facies on the basis of microgastropod diversity and trophic composition. Among them, the former three communities belong to the Holocene in addition to one in the latest Pleistocene. Research shows that the primary customers within every community are dominated by trophic category known as herbivores and gross primary customers always greatly exceed successive carnivore throughout the latest Pleistocene and the Holocene. Research also shows that microgastropod diversity and abundance in the Holocene are much richer than that in the latest Pleistocene, for example, microgastropods in the inner reef flat facies of the late Pleistocene only comprise 4 genera whereas that of Holocene 16 genera in the beach, 35 genera in the lagoon slope and 23 genera in the recent inner flat communities. It is therefore obvious that community of lagoon slope facies is the most developing stage of Holocene microgastropods and it can be further divided into three stages. In the early stage herbivores, carnivores£¬deposit-feeders and suspension-feeders appear, but with the deepening of waters the suspension-feeders disappeared and the deposit-feeders still developed to the middle stage, by comparison, equal to stage of high sea level of the middle Holocene, in which the trophic categories are the most abundant. In the late stage the deposition rate that abrupt increased may directly resulted in disappearance of a majority of deposit-feeders, but an herbivore Tricolia (Hiloa) variabilis developed particularly at this stage. The suspension-feeders occurred mainly in the early stage of the lagoon slope and the late stage of the recent reef flat in which relatively strong water turbulence may exit. The research shows that trophic feeder categories are of significance in documenting environmental change of coral reef. Acknowledgement: Project (40176030) is supported by NNSFC.