Variability in responses to nutrients and trace elements, and transmission of stressor effects through an estuarine food web

Abstract

Marine bivalve molluscs such as the blue mussel (Mytilus edulis) and the soft shell clam (Mya arenaria) have been used as sentinel organisms of contaminant bioavailability and the biological consequences of contaminant exposure. Biological responses that may contribute to the impairment of reproductive and developmental processes include responses that can be categorized as interfering with bioenergetic processes such as feeding and nutrient allocation; biosynthetic processes, such as the synthesis of energy stores; and morphogenic processes, such as those involved in structural development. Case studies within New Bedford and Boston Harbors (Massachusetts) are used to examine the relationship between contaminant uptake and effects on the reproductive cycle and bioenergetics of mussels and soft shell clams. The results observed illustrate that disruption in bioenergetics in bivalve molluscs exposed to chemical contaminants can result in loss of reproductive output and increased susceptibility to disease. Differences in the extent of reproductive impairment may be linked specifically to energetic strategies of individual species.Natural and managed ecosystems are exposed continually to natural and anthropogenic perturbations. Physical destruction of habitats, input of toxic chemicals, and nutrient enrichment leading to eutrophication are among the stressors that result in alterations in the sustainability of coastal ecosystems and a reduction in biodiversity and harvestable yields. Ecological consequences of such stressors in coastal marine ecosystems include changes in parasitic infections (Lafferty and Kuris 1999; Lenihan et al. 1999), species distributions and abundance, degradation of habitats, and changes in energy flow and biogeochemical cycles. Inputs of toxic chemical contaminants can lead to impairment of feeding, growth, development, and recruitment of fish and shellfish populations that may result in alterations in reproductive and developmental success and changes in population structure and dynamics (Capuzzo 1987). Although contaminant exposure is often viewed as a single stressor, it is only one of many stressors that all populations of marine animals experience during their life cycles. The interactive effects of contaminant exposure and natural stressors, however, are not well understood, making it difficult to establish the relationship between responses of organisms to contaminated habitats and large-scale alterations in the functioning of marine ecosystems as well as large-scale contamination of fish and shellfish resources.Although general trends in the distribution of lipophilic organic contaminants in coastal ecosystems have been defined (e.g., NOAA 1989defined (e.g., NOAA , 1991, critical information on the biological effects of contaminants, specifically on population processes, is lacking. Recent studies of the incidence of tu-