Biological Indicators

Abstract

The idea that organisms can provide an indication of the quality of their environment is widespread and basically sound but the terms `indicator' or `indicator species' may be used and understood in different ways. For example, some species are known to have particular requirements with regard to nutrients or levels of dissolved oxygen. Once these are defined, the presence of a particular species in a habitat indicates that the given determinand or parameter is within the tolerance limits of that species. It is in this sense that the term `indicator' is used here. This concept of indicators may be extended beyond simply noting the presence or absence of species. Some indicators may continue to exist in a polluted environment but suffer physiological stress which is revealed in diminished rate of growth, impaired reproductive capacity or modified behaviour. This is essentially a `bioassay' of the environmental contamination and, in allowing us to detect the change and, perhaps, estimate its intensity, the indicator has become a `bio-sensor' for that pollutant or stressor.