Southwestern Biscayne Bay Shoreline Relic Oyster Assemblage Identification, Abundance, and Hydrological Feature and Substrate Associations

Biscayne Bay, the largest estuary along southeastern Florida, is home to several species selected as ecological indicators of the Comprehensive Everglades Restoration Project (CERP). CERP aims to redistribute freshwater inflows and restore delivery volumes, thus restoring salinity habitats within the Bay. Recent literature indicates Crassostrea virginica (Eastern oyster) is the dominant oyster species in Biscayne Bay and presumes a greater extent of oyster populations and commercial harvest existed prior to alteration of hydrological regimes. Relic oyster shell density was sampled along the Bay’s southwestern shoreline at sites corresponding to historic creek and mosquito drainage ditch mouths constructed during the 20^th century, where oyster accumulations were expected to occur, and at in-between locations, where such assemblages might be more limited. Selected sites were sampled with 10 haphazardly deployed 0.25m² quadrat replicates, within which the substrate was assessed for oyster shell count to a depth of 5 cm. Contrary to previous thought, our observations revealed a species admixture dominated by C. rhizophorae (mangrove cupped oyster: ~71% of total shell count, X̄ = 6.07 shells m^-2 across all sites, max. count = 470 per 0.25 m^-2). Unidentifiable Crassostrea spp. were also abundant (26% of total shells, X̄ = 2.22 shells m^-2, max. count = 127 per 0.25 m^-2) while shells identified as C. virginica were of minor importance (3% of total shells, X̄ = 0.26 shells m^-2, max. count = 25 per 0.25 m^-2). Site-specific average oyster shell densities were significantly higher near hydrological features. Per-quadrat shell density was statistically different among substrate types. These results contribute to our knowledge of the spatial and relative abundance of relic oyster assemblages within Biscayne Bay and provide a foundation for further investigation of how oyster assemblages may be influenced by CERP implementation.