1.Due to the cost and complexity of sampling biological communities, surrogate biologicalmeasures or concentrations of toxic contaminants are often used to indicateenvironmental impacts. Such indicators can be powerful tools, but their effectivenessrequires evaluation. Mussels are widely used as bioindicators of environmental contamination.For example, physiological measurements on live mussels form the basis ofscope for growth (SFG), an integrated indicator of environmental stress. However, theeffectiveness of SFG as an indicator of community level effects has rarely been tested inthe field. 2.In this study of six sites on the west coast of the UK, the diversity of macrofaunalcommunities associated with mussels was reduced at sites with low SFG (< 10 J g-1h-1)compared with those with high SFG (> 15 J g-1h-1). At smaller scales, variation incommunity structure was related to biomass of mussels, mass of coarse sediments andthe fractal dimension of the surface of the mussel bed. 3.We measured hydrocarbon contamination as a first step in identifying contaminantsthat might underpin the relationship between SFG and diversity. Unresolved complexmixtures (UCM) are often the most abundant hydrocarbon contaminants in theenvironment, but have, until recently, been largely ignored. We found generally goodaccordance between UCM concentration in mussel tissues, SFG and diversity, butother pollutants are also likely to be involved. 4.Synthesis and applications.Our findings illustrate the complexity of relating changesin diversity to synoptic or sublethal measures of environmental stress in the field. However,the results represent a significant step towards a biotic indicator of environmental qualitythat integrates impacts across a range of levels of biological organization (from intraindividualto community). Such indicators may be of particular value in the implementationof the European Union Water Framework Directive in Europe and similar environmentallegislation elsewhere.
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