Ecosystem history of Biscayne Bay and the southeast coast

Abstract

Historical changes in South Florida related to rapid population growth in the early to mid-1900's have led to significant alteration of the natural hydrocycles and water quality of Florida and Biscayne Bays. The Biscayne Bay ecosystem shows increasing signs of distress; declines in fisheries, increased pollution, and dramatic changes in nearshore vegetation. Northern and central Biscayne Bay are strongly affected by the urban development associated with the growth of Miami. Southern Biscayne Bay is influenced by drainage from the Everglades, which has been altered by canals and agricultural activities. Restoration and preservation of Biscayne Bay and Biscayne National Park are dependent on a comprehensive understanding of the linkages between the hydrologic system and the bay ecosystem, and of the natural versus human-induced variability of the ecosystem. In this project modern surface samples were collected from 26 sites in Biscayne Bay. The primary biota analyzed were 1)benthic foraminifera, 2)ostracodes, 3)mollusks, 4)dinoflagellate cysts, 5)pollen and macro-plant material. The distribution of the biota was quantified to determine relationships with environmental conditions. These results were used to interpret historical faunal and floral changes recorded in shallow sediment cores. Water samples, ostracode and foraminiferal shells collected from the modern sediment samples are being analyzed for trace element geochemistry to derive a calibration equation to calculate absolute salinity in down-core samples. Shallow cores (1-2 meters) were collected along a north-south transect within Biscayne Bay for analysis of the downcore faunal and floral assemblages over the last 150 years. Quantitative down-core assemblage diagrams will be drawn up and the various faunal and floral data will be compared to look for correlated changes among the groups analyzed. Determinations of salinity, bottom conditions, nutrient supply and various other physical and chemical parameters of the environment will be made for each sample based on the fauna and flora present. Data from all cores will be integrated to search for regional patterns of change in diversity and distribution of the fauna and flora; data from Biscayne Bay will supplement and be correlated to onshore data and to data from Florida Bay. The integrated data set will be analyzed to see if detected changes in biota correlate to alterations in physical parameters and/or historic records of human-induced modifications of the environment. Living assemblages will be collected twice a year to provide data on habitat distribution, preferred substrates and seasonality of the living biota for interpretation of the down-core assemblages.