Report No SR3755

Oct 1994

Of the many methods available to determine pollution impact in marine benthic communities, biotic indices are the group of univariate measures that offer the most potential for the effective detection and description of impact. Codling and Ashley (1992) adapted the ITI for use in the UK for the description of pollution impact in subtidal marine macrobenthic communities. The work undertaken as part of this project has been directed at investigations into the development of a biotic index for the detect ion and description of impact in the marine intertidal and to allocate further taxa to ITI UK feeding groups.

Investigations included the behaviour of the ITI UK at MLWS, the identification of indicator taxa using a combination of multivariate methods (non-dimensional multi-dimensional scaling (MDS) and SIMPER), a phylum level meta-analysis of samples at MLWS and an index based on the observed tolerance of taxa to pollution. Each of these investigations was based on a range of data sets from Scotland and Northern Ireland.

The ITI UK was able to detect gross pollution in the Seafield beaches data set but was not able to reflect intermediate conditions in the spatial gradient. The combination of MDS and SIMPER identified 11 taxa indicative of either grossly polluted or less than grossly polluted conditions. There were insuff1cient taxa to generate a biotic index but proved useful when placing taxa along the organic pollution succession. The phylum level meta-analysis based on abundance data from samples at MLWS gave rise to two potential indices. The first, based on the relative abundances of the three major phyla in the marine intertidal (Annelida, Crustacea and Mollusca) and using the ITI UK formula, was broadly able to reflect the distinct pollution gradient in the Seafield beaches data set. The second, derived from a principal components analysis of MLWS data, was able to reflect both the spatial and temporal pollution gradients in the Seafield beaches data set The index based on the observed tolerance of taxa to pollution was applied to a range of test data sets using both raw and transformed abundance, and, where available, biomass, data This index was demonstrated to reflect known pollution gradients in time and space using abundance and biomass data where available. The effects of transformation were to either reveal, preserve or mask interpretable gradients in a number of case studies. Further taxa have been successfully allocated to ITI UK feeding groups.

None of the indices generated have been validated by correlation with other measures of pollution stress or physico-chemical variables and as such should only be applied, for any purposes, with the expert judgement of a marine benthic ecologist.

KEY WORDS Marine; intertidal; macrobenthic communities; biotic index

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