PREDATION TRACES ON FOSSIL, DEAD, AND LIVE GASTROPODS IN FLORIDA SPRINGS AND RIVERS

Freshwater spring and river environments in Florida have undergone extensive ecological changes since the late Pleistocene. Molluscan fossil and death assemblages can provide a record of these variations. Traces of predation present an important record of predator-prey interactions and can reflect changes such as the introduction of new predators, fluctuations in prey preference, and environmental disruptions such as increasing salinity. When compared to living communities, material from death and fossil assemblages document temporal and geographic trends in predation rates. In our study, fossil (shells found in situ within bank and channel sediments), death (shells accumulated loosely on the river bed), and live (living gastropods) assemblages were sampled from the Silver, Wakulla, and Ocklawaha Rivers in Florida, U.S.A. A total of 2,731 specimens representing four species were examined for predation traces: repair scars, holes, and scrapes/scours. The four analyzed species included Pomacea paludosa (n=409), Callinina georgiana (n=899), Planorbella trivolvis (n=593), and Planorbella duryi (n=830).

Live assemblages from all three rivers displayed markedly higher rates of predation (75.76%) when compared to their dead (27.08%) and fossil (34.69%) counterparts. Additionally, the Wakulla River showed higher predation rates relative to the Silver and Ocklawaha Rivers. Predation traces were more frequent in C. georgiana than other species. In addition, predation traces were more frequent in larger individuals. The increased frequency of predation traces observed in present-day populations likely reflects environmental and ecological changes in these rivers during the last ~15,000 years. The Wakulla River has experienced increasing coastal influence by rising sea levels, and all river systems have been affected by introduced species and increasing human impacts.