Effects on community structure of a pollutant gradient introduction

For determining effects of pollution at the community level, study of assemblages of benthic organisms has obvious advantages over study of the pelagos. Because of the movement of water masses, in spatial surveys one can rarely be certain how long a particular pelagic community has been in the vicinity of the pollution source, and in temporal studies the same assemblage cannot be sampled repeatedly at a particular place. Changes in benthic community structure have therefore been the mainstay in monitoring biological effects of pollutants. Tradtionally, these have largely involved studies of species abundance distributions for the macrofauna (defined in practical terms as the large species which are retained on a 0.5 or 1 mm meshed sieve when the sediment is passed through it). Species vary in their degree of tolerance to pollution so that some will decrease in abundance, some remain unaffected, and some which benefit from the changed conditions will increase (the so-called 'pollution indicator' species). A large literature has developed describing how these patterns of species abundance respond to pollution. Recently, McIntyre (1984) has commented on 'the failure of the popular benthic community monitonng approach to deliver the goods in some cases'. There are several probable reasons for this. Firstly, many natural environmental variables also modify community structure and it has not always been easy to separate these from anthropogenic effects. Secondly, studies of this kind are highly labour intensive and cannot readily be translated to regions of the world where the fauna is poorly known and a high level of taxonomic expertise is laclung. Thirdly, not enough effort has been made to identify predictable responses to pollution in other components of the benthic system such as the meiofauna (metazoans retained on a 63 pm sieve) or the