An Experimental Approach to Understanding the Response of Benthic Foraminifera to Cd, Hg, Pb and Zn

A laboratory-based experimental study was conducted to examine the abundance, diversity, and morphological response of common coastal benthic Foraminifera to the presence of a single heavy metal pollutant. Four heavy metals were chosen (Pb, Zn, Cd, Hg) based on a survey of previous field studies. Sediment was collected from a mudflat on the southern end of Sapelo Island, Georgia. Immediately after collection, sediment was sieved to separate < 63 micron fraction, which contains abundant juvenile Foraminifera. In the lab, the sediment was divided into 20 mL individual experimental aliquots. Instant ocean (40 mL) was added to maintain a salinity of ~30 psu. Individual heavy metals were added based on the EPA National Recommended Water Quality Criteria for Saltwater (Cd 40 µg/L, Hg 1.8 µg/L, Pb 210 µg/L, and Zn 90 µg/L) and increased an order of magnitude for 4 different concentration levels (duplicates and controls were also run). The experiments were incubated for four weeks, illuminated on a 12 hour cycle, and kept at a constant temperature of 18 °C. Individual samples were harvested concurrently, preserved with ethanol and stained with Rose Bengal (a vital stain). Results indicate that at the highest concentration levels, total foraminiferal abundance and diversity decreased, though increases occurred in some treatments with low contaminant concentrations. This may be explained by different pathways taken by different heavy metals. Zn and Cd were the only heavy metals that produced significant aberrant test morphologies, and the frequency of aberrant tests tends to increase with increased concentrations of the contaminant. Additionally, certain species had a higher percentage of aberrant test morphologies than others perhaps reflecting the life habits of these species. Results of this study can improve the use of Foraminifera as bio-indicators in polluted coastal environments.