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Foraminifera as bioindicators in coral reef assessment and monitoring

Coral-reef communities are threatened worldwide. Resource managers urgently need indicators of the biological condition of reef environments that can relate data acquired through remote-sensing, water-quality and benthic-community monitoring to stress responses in reef organisms. Since coral reef communities are subject to a myriad of stresses, it is critical to have an indicator of water-quality conditions that will support reef development, even in the absence of healthy coral populations following mass mortality events. Cockey et al. (1996) argued that larger foraminiferal populations, which are immune to coral-specific diseases and recover much more quickly from physical impacts than long-lived coral populations, are sensitive indicators of water-quality conditions that support reef development.

Numerous researchers have used foraminiferal studies in environmental investigations. Foraminifera play a significant role in global geochemical cycles of inorganic and organic compounds. Their tremendous taxonomic diversity and cosmopolitan occurrence make them potential bioindicators for different types of pollution. Their hard tests are readily preserved, and can record evidence of environmental stress over time. Many other factors favor their use as bioindicators: (1) they are ubiquitous to marine environments; (2) they live on and in sediment, which can act as a sink for pollution; (3) foraminifers are relatively small and abundant, permitting statistically significant sample sizes to be collected quickly and relatively inexpensively, ideally as a component of comprehensive monitoring programs; (4) the relatively short life spans of foraminifers as compared with long-lived colonial corals facilitates differentiation between long-term water-quality decline and episodic stress events; and (5) reef-building, zooxanthellate corals and foraminifers with algal symbionts have similar water-quality requirements. Hallock et al. (1995) and Williams et al. (1997) have conducted detailed studies of the key taxon Amphistegina gibbosa. Comparisons of living or total assemblages between impacted and unimpacted "reference" sites (e.g., Angel et al., 2000), comparisons of assemblages from different kinds or degrees of pollution (e.g., Alve, 1995; Yanko, 1994;1998), and comparisons of assemblages in surface samples over time (e.g., Cockey et al., 1996) can be made. Because the shells of these small protists are commonly preserved in marine sediments, perhaps the most important potential advantage may be the use of sediment cores to determine if and how much assemblages have changed at sites of interest (Hallock, 2000; Ishman, 2000).

After more than a century of study, a great deal is known about the basic biology of foraminifera. Benthic foraminifera are classified into orders based on their shell structure. Murray (1973) showed that relative proportions of the three most common benthic groups, when pl