HISTORICAL ECOLOGY OF THE SILVER RIVER, FLORIDA: COMPARATIVE ANALYSES OF LIVING, DEAD, AND FOSSIL MOLLUSKS FROM FRESHWATER HABITATS

The aquatic communities of the Silver Springs and Silver River system (Marion County, Florida, U.S.A.) have been studied by ecologists for over 50 years. In contrast, death and fossil assemblages, which preserve molluscan-components of past aquatic communities and can potentially provide a more extended historical perspective, have received limited attention. Using scuba, three types of quantitative samples were collected simultaneously at multiple sites in the upper part of the Silver River system: living mollusks (life assemblages), surficial shell accumulations (death assemblages), and river bank sediments (fossil assemblages). This approach should make it possible to evaluate changes in mollusk communities over time via comparison of living, dead, and fossil assemblages. Preliminary analysis indicates that sample standardized diversity/evenness is highest in fossil assemblages, intermediate in death assemblages, and lowest in living communities. Nonmetric multidimensional scaling (NMDS) separates live, dead, and fossil samples, with death assemblage samples characterized by intermediate faunal composition. This is to be expected as the death assemblage likely represents a mixture of the recently deceased mollusk fauna and much older (Pleistocene?) fossil mollusks that are being reworked from river banks and incorporated into surficial death assemblages. In addition, live and dead assemblage samples dominated by invasive taxa such as Corbicula fluminea (Asian Clam) form a distinct group in the ordination space. Fossil samples include a few species that are very rare or absent in the living communities and surficial death assemblages suggesting changes in mollusk communities that predate modern ecological research of the Silver River ecosystem. Comparison of the live-dead-fossil assemblage fidelity in freshwater ecosystems may augment our understanding of climatic, environmental, and/or anthropogenic changes in aquatic communities.