Effects of lead and cadmium exposure on oxygen respiration rates of individual Antarctic foraminifera during agglutinated shell formation

Heavy metal exposure from anthropogenic pollutants negatively affects many marine organisms, including foraminiferan protists. As such, foraminifera are often used as bioindicators of stressed environmental conditions. Primary research has commonly focused on how heavy metals affect foraminiferal assemblages, ultrastructure, and shell morphology; however, little if any data have been reported on how heavy metals affect their physiological functions. Here we measure respiration rates of individual foraminifera after acute exposure to three concentrations of toxic but sub-lethal levels of lead (Pb) and cadmium (Cd). These experiments relied on the large cell size of an agglutinated Antarctic foraminifer, Astrammina rara. Cells were isolated from sediment collected by scuba divers in Explorers Cove, Antarctica. In the laboratory, individual, live cells were removed from their shells and placed in sealed respirometry chambers with either normal or Pb- or Cd-spiked artificial seawater. Cells in the process of shell formation were used to ensure that all individuals were aerobically active and in similar metabolic states. Noninvasive oxygen-sensing optode technology was used to measure oxygen consumption during the first 24-36 h of shell formation. The average respiration rate was 1.07 nmol O-2 h(-1) (range 0.78-1.84 nmol O-2 h(-1)) for normal cells. We compared the results from each exposure group to this baseline rate and found that both Pb and Cd significantly suppressed the respiration rate of A. rara in all but the highest level of Pb exposure. This study provides a novel, powerful, and short-term way to measure foraminiferal physiological responses to heavy metal toxicants.