Introduction

The subject of indicators and indices (and difference between them) was introduced in Ch. 3 in the context of environmental reporting. The terms indicator and index are used here in the same way as they are used by Slocombe (1992). The purpose of this chapter is to provide examples of biological indicators (such as indicator species) and biological indices (such as water quality indices).

Biological indicators range from single organisms through populations and species to biological communities. Biological indices are derived from attributes of biological communities (such as abundance and sensitivity to pollution). Physical disturbance and changes in environmental variables such as temperature or salinity result in change in variables such as the species composition of the biotic community. Such community changes can, therefore, usefully be monitored to assess current states of the environment and also in a predictive sense in relation to environmental assessments (see Ch. 10).

The use of species indicators and community indices has grown rapidly, particularly in relation to monitoring water quality. There has also been much detailed research on the use of biological indicators for the detection of pollution and specific pollutants. Biological variables and indicator species used for monitoring of pollutants are many and varied, ranging from cells, tissues and organs to whole organisms (Table 5.1) including unicellular organisms, plants and animals.

Plant and animal biological indicators

Presence and absence

Earlier (p. 22) there was reference to Alister Hardy's description of plankton monitoring.