WHY DOES TREMATODE PARASITE PREVALENCE SURGE DURING SEA-LEVEL RISE?

Digenean trematodes (Platyhelminthes) are complex life cycle parasites found in aquatic environments. These flatworms commonly infest a variety of invertebrate taxa that serve as first and second intermediate hosts; a vertebrate predator that serves as the definitive host consumes the latter. Similar to many extant parasites that are small and soft-bodied, trematodes do not have a body fossil record; however, they can be represented by characteristic pathologies induced in the shells of their bivalve mollusk intermediate hosts. We have investigated the occurrence of these malformations in Quaternary, Holocene, and recent estuarine, lagoonal, and shallow marine settings. Our work consistently demonstrated a significant increase in parasite prevalence (the proportion of individuals with pathologies within a con-specific sample) associated with sea level rise on millennial and centennial time scales and among modern coastal depositional environments that serve as analogs for such settings during sea level rise and fall. Why is this the case? We have examined a variety of biotic and environmental factors and have largely ruled out changes in salinity (based on taxonomic data), richness, evenness, diversity, community structure, and taphonomy as drivers of this pattern. We are utilizing trace element sclerochemistry of bivalve host taxa from modern and fossil settings to determine the influence of temperature, salinity, and nutrient delivery/hypoxic events on increased parasite prevalence.