Microgastropod trophic structure of the Yongshu reef, South China Sea, since the late Pleistocene in relation to paleoenvironment

摘要

Microgastropods from the upper part of the Nanyong-1 core at Yongshu reef, South China Sea, are used for investigating the trophic structure in relation to paleoenvironment. Quantitative analyses on the trophic categories of microgastropods show that the trophic categories and their relative contents are variable in different communities of the Holocene and the late Pleistocene, including the recent inner reef flat, lagoon slope, gravel beach and inner reef flat communities in descending order. The trophic categories in the Holocene are more abundant than that in the late Pleistocene. In the Holocene, the largest number of individuals of trophic categories appeared in the middle stage of the lagoon slope, corresponding to a period of high sea level during the Holocene. However, four kinds of trophic categories such as herbivores, carnivores, deposit-feeders and suspension-feeders, occurred together only at two significant stages, the early stage of lagoon slope and the late stage of recent reef flat, when suspension-feeders, indicators of stronger water turbulence, existed. The deposit-feeders most abundantly occur in the lagoon slope communities, especially when the lagoon gradually deepened along with rising sea level at the early and middle stages of the lagoon slope. When the depositional rate suddenly increased during the middle late stage of the lagoon slope, the deposit-feeders disappeared probably due to increasing coarse sediment and a lack of fine organic matter. It is interesting that an herbivore Tricolia variabilis (Pease) became very rich, occupying 30% of all individuals in the sample. This indicates that the species may grow preferentially under conditions of high depositional rates.