A strategy is presented for analysing marine biological survey data and relating the biotic patterns to environmental data. To avoid circular argument, biotic and environmental data are kept separate. The strategy is illustrated by a worked example using data on the distribution of 182 nematode species in 107 samples in the River Exe estuary. Nineteen stations are grouped Into 4 main clusters using complementary classification and multi-dimensional scaling (MDS) ordination techniques. These are both based on root-root transformed abundance data with the Bray-Curtis measure of similarity. Indicator species characterising each group are extracted using information statistics. Inverse analyses give clusters of CO-occurnng species which are strongly related to the station groups. Relationships of station groups to environmental variables are revealed by superimposing data for one variable a t a time on the MDS plot, showing that some station groups differ in sediment granulometry and others in salinity, for example. Some of the other factors plotted show no difference between station groups. Similarly, physiognomic charactcrlstics of the species are superimposed on the MDS plots of the inverse analysis of species groups, revealing differences in setal length and trophic status between the species groups. Finally, the 4 major station groups and species groups are related to one another in terms of morphological adaptation to the habitat.

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Taxonomic distinctness is a unlvanate (bioldiversity index which, In ~t s simplest form, calculates the average 'distance' between all pairs of species in a community sample, where thls distance is defined as the path length through a standard Llnnean or phylogenetlc tree connecting these species. It has some appealing properties: ~t attempts to capture phylogenetic diversity rather than simple richness of species and is more closely linked to functional diversity; it is robust to vanation in sampling effort and there e x~s t s a statistical framework for assessing ~t s departure from 'expectation'; it appears to decllne monotonically in response to env~ronmental degradation whilst being relatively insensitlve to major habitat differences, and, in its simplest form, ~t utillses only simple species lists (presence/ absence data). Many of its practical characteristics remain to b e explored, however, and this paper concentrates on the assumptions made about the we~ghting of step lengths between successive taxonomic levels (species to genera, genera to families etc.), which when accumulated glve the overall path lengths. Uslng data on free-llving manne nematodes from 16 localit~es/habitat types in the UK, it is shown that the relative values of taxonomic distinctness for the 16 sets are robust to vanation in the definition of step length. For example, there is a near perfect linear relationship between values calculated using a constant increment at each level and a natural alternat~ve in w h c h the step lengths are proportional to the number of species per genus, genera per family, family per suborder etc. These weightlngs are then manipulated in more extreme ways, to capture the structure of phylogenetic divers~t y in more detail, and a contrast is drawn between the biodiversity of island (the Isles of Scilly) and malnland (UK) locations and habitats. This paper concludes with a discussion of some of the strengths and weaknesses of taxonomc distinctness as a pract~cal tool for assessing biodiversity.

Reductions in number of species and diversity and increased dominance of opportunistic species occurred late in the sequence of response to oil as a stress factor (within 500 to 1000 m of discharge sources). However, multivariate analyses, (classification analysis using the Bray-Curtis dissimilarity index) and ordination (multi-dimensional scaling) clearly distinguished site groupings related to oil activities at distances of up to 2 to 3 km from the Ekofisk pollution source and up to 1.5 km from the Eldfisk source. The first recorded changes in benthic communities in response to oil were increased abundance patterns of some species and changes in the presence and absence patterns of rare species, with species being mostly present in one site group and mostly absent in another site group. Only under severe pollution did the opportunistic species, which have often been suggested as universal indicators of pollution, dominate. The major site groupings could still be distinguished after aggregation to higher taxa (families and even phyla) when using multivariate analyses. If this finding proves to be a general one then great savings in time and effort, with little or no loss of precision, wdl be possible in environmental monitoring.