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

Abstract

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 sedlment 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, 4 2 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 drihng 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.

Relationships between spatial patterns of benthic assemblages in a mangrove forest using different levels of taxonomic resolution

“…changes at the level of orders or phyla. Olsgard et al (1997) simultaneously examined effects of altering taxonomic resolution and transforming the data on results of ANOSIM tests on soft-sediment macrofauna along a gradient of pollution. They, too, found that transformation had stronger effects on the measured patterns than dld changing resolution, with decreased ability to identify pattern for analyses of strongly transformed data at the coarsest taxonomic resolution.…”

“…From a study of the literature, there appears to be an automatic tendency to transform data to X o Z 5 before proceeding with ANOSIM or nMDS plots. Both the transformations and levels of taxonomic resolution used can strongly influence the significance of any results obtained (Olsgard et al 1997) and should be carefully considered in the light of the hypotheses being tested before each is selected.…”

Molluscan diversity along a Mediterranean soft bottom sublittoral ecotone

“…The use of different sieve mesh sizes (Thompson et al, 2003) and the application of subsampling techniques (Carey and Keough, 2002) have been proposed for the establishment of more cost-effective methods. Additionally multivariate techniques (Olsgard et al, 1997) and recently developed sample-size/sample-effort free biodiversity indices have also been used as an alternative to species-level identification of the total fauna (e.g. Warwick and Clarke, 2001).…”

Cross-community congruence of patterns in a marine ecosystem: Do the parts reflect the whole?

“…As has recently been shown in some coastal systems (Worm et al 2002), the effects of consumers and nutrients on diversity consistently depend on each other, and the direction of their effects and peak diversity shift between sites of low and high productivity. Also, as this is a case of communities linked with predator-prey interactions, it is possible that the effects of disturbing the higher trophic levels (fish) are likely to cascade down the lower trophic levels as shown by Worm & Myers (2003) for open sea ecosystems.In cases such as monitoring of pollution and other types of anthropogenic stress, macrofauna and the associated surrogates can be very useful as has been shown in many studies for different types of effects (Warwick 1988, Olsgard et al 1997, Dauvin et al 2003. In this particular context, monitoring is designed to detect, for instance, the spatial extent of disturbance using community structure and diversity as a sensitive tool.…”