Abstract
Naples Bay, a highly urbanized estuary, has lost an estimated 80% of its oyster reefs since the 1950s due to dredging and development activities. Artificial canals, primarily the Golden Gate Canal, have increased freshwater flows into Naples Bay causing extreme swings in salinity. This study characterizes the health of the eastern oyster, Crassostrea virginica, at four sites along a salinity gradient by investigating and correlating various oyster responses to salinity, dissolved oxygen, and temperature. Prevalence and intensity of Perkinsus marinus infection varied significantly among sites, with the northernmost upstream Site 1 showing the lowest infection. Condition index varied significantly among sampling months and sites, and decreased during the spawning period, April through October. Sites 1 and 2, with more optimal salinities for the first 8 months of the study, had the highest mean condition index. Significant differences were found among sampling months for spat recruitment and sites and peaked in August. Spat recruitment was greatest at the southernmost Site 4 which is located furthest from the freshwater influence and therefore has less extremes in salinity. Living densities (# live oysters m-2) also varied significantly among sampling months and sites, with living densities increasing when moving downstream. Higher living densities were found in the wet season than the dry season reflecting recruitment occurring onto the reefs. The wet season is when extreme swings in salinities result upstream which corresponds with oyster reproduction. Site 1 experienced a 31 ppt drop in salinity within a few days in July when significant rainfall began. This is a tremendous stressor on oysters and could result in mortality of juvenile oysters and the flushing of spat downstream due to high freshwater flows. This study highlights that freshwater flows and resulting salinities are a driving force for oyster reef health and distribution in Naples Bay. It also provides a baseline assessment of the oyster population that will allow for future comparisons when water quality improves due to diversions of freshwater from the Golden Gate Canal. These diversions are planned for the near future by the South Florida Water Management District. This study also assists resource managers in determining potential oyster restoration sites in the bay. Management recommendations include focusing oyster restoration sites at the downstream locations due to less salinity extremes, high oyster living densities, and higher spat recruitment.