Stable isotopic analysis (δ 18O and δ13C) and characterization of the ostracode community structure were carried out from a high-resolution sediment-core recovered from Oyster Bay in the west of the Everglades National Park. Because of its location, between the Shark River Slough (SRS) and the Gulf of Mexico, the Oyster Bay core locality experiences extreme salinity fluctuations due to the interaction of freshwater run-off, precipitation, and marine water inputs. Ostracode population dynamics and isotopic variability over the 20th century are linked to natural and anthropogenic forces that affect the South Florida coastal ecosystem on interannual to decadal time scales. Three ostracode assemblages can be recognized within the 100-year sediment-core record: the first extending from the turn of the century to about 1950; the second, from the early 1950s to the late 1970s; and the third to core recovery in 1995.
An abrupt decrease in ostracode abundance, species diversity, and shifts in species dominance occur in the mid-1980s and reflect episodes of environmental stress. Markedly enriched δ 18O values from the ostracode Peratocytheridea setipunctata and the benthic foraminifer Ammonia parkinsonia typica at this time are concurrent with a major regional drought in South Florida, as well as with documented algal blooms and major die-off of sea grasses in Florida Bay. In addition, the timing of these events is contemporaneous to the onset of the South Florida Water Management District (SFWMD) "Rainfall Plan" and the closing of the Buttonwood canal. Higher ostracode abundance and species richness occurs between the late- 1950s and late- 1970s. Stable isotopic data and ostracode assemblage characteristics suggest a period of relative environmental stability and possibly improved water circulation in Whitewater Bay and Oyster Bay. Fluctuations in community structure during this time are more systematic and appear to be temporally correlated to rainfall variability patterns. Water management policies at this time are also discemable from the microfaunal and isotopic record, particularly the Congressionally mandated Monthly Minimum Allocation Plan of water supply to SRS. Before 1950, hurricane events and their effects are the major cause for immediate modifications within the ostracode community, though our data show that ostracode populations are capable of rapid recovery. Over the complete record of the last century, the effects of water management practices can be assessed from information embedded in the ostracode record. Nevertheless, the effects of natural climatic variability in Oyster Bay appear to outweigh the impact of anthropogenic forces.
Available at: http://works.bepress.com/patricia-blackwelder/38/