Benthic foraminifera are important environmental indicators of heavy-metal contaminants in marine environments because of their unique sensitivity to environmental change. However, this sensitivity can make parsing the effect of contaminants from other factors such as salinity and temperature difficult. To address this problem, this study individually compares the effects of heavy metals nickel and zinc on temperate rotalids and subtropical miliolids under different temperature and salinity regimes, including intermediate (22°C, 32 psu), elevated temperature (30°C, 32 psu), reduced temperature (18°C, 32 psu), elevated salinity (22°C, 40 psu), and reduced salinity (22°C, 12 psu). Assemblages of foraminifera were grown experimentally from propagules (small juveniles) collected from two shallow marine sites: Sapelo Island, Georgia, and Little Duck Key, Florida. Surface sediment was collected from both locations and sieved immediately after collection. Using the propagule method, assemblages of foraminifera were grown in a controlled setting from propagules in these sediment samples. Either nickel or zinc was added to each assemblage. Experimental conditions were held constant with only metal concentration, salinity, and temperature varying.
Exposure to elevated concentrations of nickel and zinc led to limited foraminiferal abundances compared to the controls under all temperatures and salinity conditions examined. In addition, high concentrations of nickel and especially zinc resulted in an increase of deformed tests of Sapelo Island foraminifera under intermediate (22°C, 32 psu) and high salinity (22°C, 40 psu) conditions. Far fewer deformities occurred in Sapelo Island assemblages in higher or lower salinities and temperatures. These results support the usefulness of foraminiferal abundance and species abundance as tools for environmental analysis. Consistent with previous work, results also identify the problems associated with using test deformities alone as a bioindicator tool.