USE OF SEAGRASS-ASSOCIATED FORAMINIFERA AS AN INDICATOR OF PAST WATER QUALITY

The occurrence and abundance of seagrass is well correlated with the environmental water quality of coastal areas. To address the general question of how much variability in water quality has occurred naturally and how much is due to human perturbation, we developed an approach to quantifying seagrass abundance of the past few hundred years. The study area is Florida Bay, which drains the environmentally challenged Everglades. Ideally, one would examine the abundance of seagrass buried in marine sediments through time, but seagrass is not well preserved in the fossil record. Instead, we have used the abundance of seagrass-associated foraminifera. For this study, we define seagrass-associated foraminifera as those primarily associated with seagrass, i.e., benthic foraminifera that occur more on seagrass than in or on sediments.

We collected sediment samples in replicate from densely seagrass-vegetated, sparsely seagrass-vegetated, and unvegetated areas of eight sites ranging from northeastern to southwestern Florida Bay. Sites were chosen for their proximity to water quality monitoring stations and to maximize differences in geographic location and physical conditions. Foraminifera prepared from the samples were counted as either seagrass-associated or nonseagrass-associated, based on ecological relationships described in the literature and observed in ongoing surveys of seagrass epiphytes. The counts were submitted to Analysis of Variance to test the significance of the variables site and seagrass density, and their interaction. Preliminary results from three sites (Trout Cove, Butternut Key, Bob Allen Keys) with the three levels of seagrass density produce nonsignificant results (N=27, p=.15). However, if only the densely vegetated and unvegetated values are included (excluding sparsely vegetated), the abundance of seagrass foraminifera is weakly correlated with seagrass density (N=18, p=.07). Our first results suggest that there is potential for the use of foraminifera as a proxy of seagrass abundance to assess water quality of the past.