The application of trophic structure of fossil communities in paleoenvironmental reconstruction

The relative abundance of suspension- and deposit-feeding organisms in fossil communities has been used to interpret water turbulence in ancient environments. Trophic analysis of modern molluscan communities of San Francisco Bay and of Pliocene macroinvertebrate communities of the Kettleman Hills, California, suggests that the method is only partly valid for inshore environments, which may be more complex than those previously studied. Factors other than water turbulence must explain some differences in trophic proportions. Epifaunal communities consist largely of suspension-feeding organisms regardless of other environmental factors, and relict sediments or sediments out of equilibrium with the normal hydrologic conditions in the area may lead to erroneous interpretations. Analysis of the total benthic macroinvertebrate communities of the southern California shelf indicates that the trophic proportions of the potentially fossilizable part of each community are not the same as the total community and is not always diagnostic of the environment.