MEPS 149:173-181 (1997)  -  doi:10.3354/meps149173

Relationships between taxonomic resolution and data transformations in analyses of a macrobenthic community along an established pollution gradient

Olsgard F, Somerfield PJ, Carr MR

Although surveys of soft-bottom macrofauna are an important tool in marine pollution monitoring, the high costs involved have often been criticised. Species identification is time-consuming, and one solution is to identify organisms to a taxonomic level higher than species. This study, using data from a survey in the vicinity of the Valhall oil field in the Norwegian sector of the North Sea, examines the effects of using abundances of different taxonomic levels, and of using different data transformations (used to adjust the relative weightings of rare and abundant taxa) in subsequent multivariate analyses of faunal patterns, and relates the environmental variables to the observed faunal patterns from the different analyses. The study area has a constant water depth, homogeneous bottom sediment and a uniform benthic community. At the time of the survey the platform had been active for 9 yr, and strong gradients in environmental contaminants and related faunal changes were found. Data from 27 stations around the oil platform were analysed at the levels of species, genus, family, order, class and phylum, using a range of data transformations and multivariate techniques. The data matrix contained 156 species grouped into 138 genera, 102 families, 42 orders, 18 classes and 10 phyla. Matrices derived from species, genus and family abundances constructed using the same transformation are very similar, and even at higher taxonomic levels the gradient of change in community structure is still detectable. As the taxonomic level increases the effects of transformations become stronger, so although both taxonomic resolution and transformation affect the results of analyses, the effects of each are different and, to a large extent, unrelated. The highest correlations between matrices derived from measured environmental variables and biotic matrices are between environmental variables related to drilling activity and mildly transformed family abundances, suggesting that analyses of higher taxonomic levels are more likely to reflect a contamination gradient than are analyses based on species abundances. Before any general recommendations regarding taxonomic levels are given for future macrobenthic surveys, there is an obvious need for studies of weak, intermediate and strong gradients in various types of contamination in homogeneous and heterogeneous environments, using the same sampling and analysis methods.

Taxonomic resolution · Transformation · Macrobenthos · Environmental variables · Multivariate analysis · Pollution monitoring · Cost-effectiveness

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