Effects of heavy-metal contaminants (Cd, Pb, Zn) on benthic foraminiferal assemblages grown from propagules, Sapelo Island, Georgia (USA)

Abstract

Abstract Benthic foraminifera have long served as indicators of environmental conditions – both natural and anthropogenically impacted. To better understand the responses of benthic foraminifera to specific heavy metal contaminants (Cd, Pb, Zn), assemblages of coastal benthic foraminifera were grown from propagules (tiny juveniles) in the lab with exposure to a single heavy metal over a range of concentrations, based on the US Environmental Protection Agency's Critical Maximum Concentration (CMC) values. Foraminiferal propagule banks were collected from relatively pristine mudflats, located on the southern end of Sapelo Island, Georgia (USA). Consistent with the findings of numerous field-based studies, foraminifera were found to respond negatively to Cd, Pb, and Zn. Overall, assemblages grown with exposure to higher concentrations of these metals are characterized by decreased abundances, species richness, and evenness. All of the acute responses observed in these metrics occur at concentrations equal to or somewhat higher than the USEPA's CMC values. Foraminiferal responses vary by metal, though the four most common species (two monothalamids: Ovammina opaca Dahlgren, Psammophaga sapela Altin Ballero, Habura, Goldstein; and two rotaliids: Haynesina germanica (Ehrenberg), Ammonia tepida (Cushman)) responded in a broadly similar fashion. The monothalamid species however may be more sensitive to high concentrations of each metal. Of the metals examined, exposure to Pb had the most deleterious effect, followed by Zn, then Cd. These four most abundant species appear to be more tolerant of Cd than the other metals. Zn was the only metal in the study that produced abundant aberrant test morphologies. Ammonia tepida grew abnormally more frequently than any other species encountered and exhibited a distinctive enlarged aperture as well as aberrant patterns of calcification, chamber arrangement, and enlarged pores. Abnormal tests were also found in H. germanica and a miliolid. The monothalamid species did not produce aberrant test morphologies. Results support the application of foraminifera as bio-indicators in polluted environments.