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EXTENDED ABSTRACT: An Experimental Approach to Understanding the
Response of Benthic Foraminifera to Cd, Hg, Pb, and Zn
Ellen R. Brouillette and Susan T. Goldstein
Department of Geology, University of Georgia, 210 Field St., Athens, Georgia 30602
Benthic foraminifera respond quickly to changes in environmental parameters such as salinity, temperature, water depth, grain size, and increased environmental stress caused by pollution (Murray, 1991; Scott et al., 2001). To understand better how foraminifera respond to individual pollutants, a laboratory-based experimental study was conducted to examine the abundance, diversity, and test deformation response of common coastal benthic foraminifera to the presence of heavy metal pollutants. Four heavy metals were chosen (Pb, Zn, Cd, and Hg) based on observations from previous field studies (Magistrato alle Acque di Venezia, Thetis, 2008). Sediment was collected in October and June 2008 from a mudflat on the southern end of Sapelo Island, Georgia. In the field, sediment was sieved to separate the <63 micron fraction, which contains abundant juvenile foraminifera (Alve and Goldstein, 2003). 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 mg/L; Hg, 1.8 mg/L; Pb, 210 mg/L; and Zn 90, mg/L) and increased an order of magnitude for 6 different concentration levels (duplicates and controls were also run). The experiments were incubated for 4 weeks, illuminated on a 12 hour cycle, and kept at a constant temperature of 18°C for the duration of the experiment. The samples were individually harvested at the same time, preserved in ethanol and stained with Rose Bengal (Walton, 1952) to determine which foraminifera were alive at the end of the experiment.
Experimental assemblages were dominated by Ammonia tepida, Haynesina germanica, Psammophaga simplora, and Ovammina opaca. Additional taxa present include Miliammina fusca, Buliminella elagantissima, Textularia palustris, Textularia candeina, Triloculina sp., Quinqueloculina jugosa, Quinqueloculina polygona, Quinqueloculina seminula, and Bolivina lowmani. Aberrant test morphologies were observed in some species that grew with exposure to Zn or Cd (Fig. 1). Aberrant test morphologies were most common in assemblages grown with exposure to Zn at 90,000 mg/L where ~23% of the total assemblage was deformed. While this number may seem small it is important to note that non-polluted sites host 1-3% deformations. Individual species exhibited different responses. Populations of Haynesina germanica contained ~52% deformations, whereas those of Ammonia tepida contained ~22%. No deformations were present in the common monothalamous agglutinated species Ovamina opaca and Psammophaga simplora (Fig. 2). The differences between species may be related to their different life habits (e.g., diet, mode of test growth, and metabolism) or type of shell construction. Results indicate that at the highest concentration levels, total abundance and diversity of foraminifera decreased (Fig. 3). In some cases, these trends do not decrease uniformly, but fluctuate somewhat (Fig. 2). This may be explained by potentially different pathways taken by heavy metals in individual aliquots. Alpha diversity also decreases with an increase in Cd, Pb, and Zn; and increases in the presence of Hg (Fig. 4).
In conclusion, foraminifera respond negatively to the presence of different heavy metals. This is observed in the decrease in foraminiferal abundance and diversity, and an increase in aberrant test morphologies. While more studies are needed to fully understand the relationship between the presence of heavy metal pollutants and foraminifera, this study provides exciting initial data that supports the use of benthic foraminifera as possible bio-indicators.
Alve, E., and S. Goldstein, 2003, Propagule transport as a key method of dispersal in benthic foraminifera (Protista): Limnology and Oceanography, v. 48, no. 6, p. 2163-2170.
Magistrato alle Acque di Venezia, Thetis, 2008, SIOSED Project, final report of research activities developed during 2005-2007: Venice Water Authority Concessionary, Consorzio Venezia Nuova, Italy, 52 p.
Murray, J. W., 1991, Ecology and palaeoecology of benthic foraminifera: Longman Scientific and Technical, Harlow, U.K., 365 p.
Scott, D. B., F. S. Medioli, and C. T. Schafer, 2001, Monitoring of coastal environments using Foraminifera and Theocamoebian indicators: Cambridge University Press, Cambridge, U.K., 176 p.
Walton,W. R., 1952, Techniques for recognition of living foraminifera: Contributions from the Cushman Foundation of Foraminiferal Research, v. 3, p. 56-60.
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