Community and population indicators of ecosystem health: Targeting links between levels of biological organisation

Risk assessments have regularly utilised analysis at the community level as a tool for determining the health of an aquatic system. Using relevant examples, the pros and cons of community level investigation are reviewed, highlighting both the recent advances employing coarse levels of taxonomic identity and the suitability of fish communities for such analyses. Community structure, however, is merely an expression of variation in the populations of the constituent species and the response of these populations to environmental stress. In turn, the maintenance of populations is dictated by the input of individuals within that population in terms of growth (biomass) and reproductive output (persistence), parameters which can provide useful information on the health of a system. It is therefore important to explore the mechanisms linking the different levels of biological organisation to understand how individual toxicological responses may be expressed at the community level and conversely what mechanisms are producing observed community structures in stressed systems. This also has consequences in terms of risk assessment, determining which level of organisation provides the most sensitive and robust method of assessing environmental health.