Journal of Foraminiferal Research, v. 39, no. 4, p. 278–299, October 2009
STRATEGIES FOR USING SHALLOW-WATER BENTHIC FORAMINIFERS AS BIOINDICATORS OF POTENTIALLY TOXIC ELEMENTS: A REVIEW MICHAEL MARTÍNEZ-COLÓN1,3, PAMELA HALLOCK1 AND CARLOS GREEN-RUÍZ2 ABSTRACT
This review examines environmental factors affecting potentially toxic elements (PTEs) in coastal waters with the goal of proposing ways to enhance the use of benthic foraminifers as bioindicators of such pollution. Pollution of coastal systems by PTEs, often referred to as heavy metals, is a major concern for scientists, resource managers, and regulatory agencies. Bioavailability, uptake rates, speciation, clay mineralogy, pH, complexation, and other factors control the behavior of PTEs in marine systems, especially in estuaries. While breakthrough work has examined incorporation and assimilation of metals into marine macroinvertebrates, similar research on marine protists is still in the developmental stage. Many studies assume or conclude that foraminiferal assemblages and the frequency of deformed tests are first-line indicators of pollution, but others present confounding results. Understanding the complex geochemistries of PTEs, coastal waters, and sediments is critical to the design and interpretation of meaningful studies. Applications of foraminifers as bioindicators require strong scientific models based on both field and laboratory experiments and which specifically examine the influence of PTEs and other pollutants at community, assemblage, population, individual, and gene-expression levels. Genomic studies of key foraminiferal taxa with strong potential as bioindicators are critically needed as a basis for studies of gene expression indicating exposure to specific stressors. Though major challenges exist to fully realizing the potential for application of foraminifers as environmental indicators, their global importance in the past and present argues strongly for further development of these promising tools.
point sources of pollution such as atmospheric fallout and storm-water runoff are now quantitatively more important than point sources in many managed areas. The material introduced into aquatic environments by non-point sources is typically neither well defined nor readily managed, even where the political will exists to do so. Potentially toxic elements in estuarine sediments have been studied both spatially and temporally for many years. Work by Tessier and others (1979), Santos and others (2005), and many others have laid the ground work for further research on how individual pollutants affect specific organisms, including microbiota. Complicating factors for understanding responses of organisms in estuarine environments include natural variability in pH, salinity, sediment texture and mineralogy, and organic productivity, all of which are linked to climatic and geographic regions and to the complexity of the subject organisms. A variety of approaches has been developed to identify pollutants in coastal waters. Pollutants have been measured in both the water column and substrate (e.g., Kot and others, 1999; Zhang and others, 2002). Their effects have been studied on many marine organisms, including fish, decapods (Rainbow and White, 1989; Rainbow, 1995), planktic crustaceans, ostracodes (Eagar, 2000), and benthic foraminifers (Coccioni, 2000; Elberling and others, 2003; Farkas and others, 2003; Le Cadre and Debenay, 2006; Frontalini and Coccioni, 2008). Benthic infauna generally are preferred for bioassays and as bioindicators because they are typically sessile or of limited mobility and therefore are directly influenced by natural or induced stresses in their environment (Bilyard, 1987).
INTRODUCTION
OBJECTIVES
Water pollution has been an environmental concern since the onset of the Industrial Revolution. Anthropogenic activities (i.e., agriculture, mining, industrialization, urbanization) have contaminated surface, ground, and coastal waters with excessive nutrients and potential toxins (Hunter and Arbona, 1995; Alve, 2000; Elberling and others, 2003; Farkas and others, 2003; Green-Ruı́z and Páez-Osuna, 2004; Hayward and others, 2004). These pollutants can alter ecosystems by reducing the fecundity and survival of organisms, and they can promote diseases that can be passed to humans (Smedley and Kinniburgh, 2005). Historically, point sources such as industrial effluent and sewage outfalls were among the major sources of water pollution. Because point sources can be managed, non-
This paper comprises two sections that address two major objectives. The first objective is to provide an overview of environmental factors influencing mobility and bioavailability of potentially toxic elements (PTEs) in coastal waters. This section can provide researchers and resource managers, who are proposing or beginning to work with PTE contamination, with insight into the complex range of factors and environmental conditions that must be considered, keeping in mind that PTEs are too diverse and complex in their chemical behaviors to permit a comprehensive treatment in a review paper. The insight provided by the first section is essential for the second objective, which is to encourage research on how PTEs affect benthic foraminifers and, in turn, on how foraminifers can be used as bioindicators of pollution. This section examines previous studies of benthic foraminifers in coastal waters contaminated by PTEs. Benthic foraminifers are ideal tools in environmental research because they are small, abundant, diverse, and include stress-tolerant taxa. In addition, foraminifers have shells that leave a record of
1 College of Marine Science, University of South Florida, St. Petersburg, FL 33701, USA 2 Instituto de Ciencias del Mar y Limnologı́a, Universidad Nacional Autónoma de México, Mazatlán-México 3 Correspondence author. E-mail: mmartin8@mail.usf.edu; foram3438@yahoo.com
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