ASSESSING PALEOSALINITY, SHORELINE POSITION, AND FRESHWATER INFLUX IN COASTAL ECOSYSTEMS USING MOLLUSCAN FAUNA

Coastal ecosystems, where freshwater, terrestrial, brackish and marine ecosystems meet, are dynamic environments. Human occupation of the coasts and concerns about future sea level rise and climate change impacts have made it essential for resource managers and urban planners to understand past rates and processes in these transitional environments. For example, where were the coastal habitats located in the past and how rapidly did they migrate; how much freshwater was delivered to the coast; did erosional and depositional processes balance out; what was the frequency and intensity of storms? Mollusks are a valuable tool to assess past conditions because they are found in almost all habitats on earth and are ideal fossils for quick assessments of where a sample was deposited – terrestrial, freshwater, brackish, or marine. Also, their size (usually visible to the eye) and preservation potential (generally hard-shelled) add to their usefulness. By comparing fossil assemblages with modern data on salinity and habitat preferences for individual mollusk species, we are able to make relatively precise estimates of past salinity and shoreline position. In a case study comparing weighted-average salinity estimates based on living molluscan assemblages with instrumental data, Wingard and Hudley (2012) reproduced salinity estimates within 2 ppt (parts per thousand) in the Florida Bay estuary. This technique was applied to sediment cores to reconstruct coastal salinity changes over the last 100-500 years. These molluscan-based paleosalinity data were incorporated into hydrologic models to extend estimates of freshwater flow into the estuary to pre-instrumental time periods. Understanding natural hydrodynamic conditions in coastal ecosystems of the past provides insights into potential management, mitigation and adaptation strategies that may work for coastal communities in the coming century.