DISTRIBUTIONS OF LIVING AND FOSSIL MOLLUSKS AS ASSESSMENT TOOLS FOR RESTORATION OF SOUTH FLORIDA

South Florida is undergoing an extensive restoration effort focused on establishing more natural freshwater flow through the Everglades to enhance the resiliency of the ecosystem. Alterations in freshwater flow through water management structures and practices throughout the 20^th century not only impacted the wetlands and the biodiversity of south Florida, but also the estuaries and coastal ecosystems. The areas closest to the shoreline in Florida Bay and Biscayne Bay have undergone some of the most significant shifts in salinity regimes. Molluscan assemblages in sediment cores from nearshore locations indicate less saline conditions in the older/lower portions of the cores compared to the more euryhaline assemblages in the younger/upper portions of the cores.

To better interpret the core assemblages and provide paleosalinity estimates to restoration managers, we have been conducting surveys of living mollusks and their habitats in south Florida since 1994, building a dataset with environmental information on 222 species from 231 sites (available at https://www.sciencebase.gov). However, our surveys are taking place in an already altered ecosystem, with the majority of our measurements in salinities >18 psu. It is the oligohaline (0.5 to 5 psu) and mesohaline (5.01 to 18 psu) salinity regimes that resource managers are hoping to restore to the nearshore areas of the estuaries. To increase our understanding of the lower salinity regimes and species present in the older core segments, we have moved our sampling further upstream and/or targeted enhanced wet periods with more freshwater discharge. In August of 2021, we visited 30 shoreline and upstream sites and documented 53 molluscan species; the additional abundance data increases our confidence in our salinity estimates for the low salinity species.

The pre-alteration distribution of mollusk species in our cores provided a guide to which species may be indicative of low salinities. Our recent efforts focused on obtaining salinity tolerance data for those species in the modern environment. The modern data in turn provide quantitative data to improve our paleosalinity estimates for restoration targets. Combined, the core and modern data provide a list of molluscan species that may serve as good indicators for restoration performance measures.