No abstract

The comparison of species complements within and between habitats and geographical areas is a fundamental aspect of ecological assessments. However, many influences resulting from variability in sampling and data analysis often hinder the ability to determine important patterns in community structure. The study is based on the hypothesis that using a standard sampling method, an asymptote in the rarefaction curve represents the total (gear-specific) species complement likely to be encountered for the geographical area. Accordingly, an asymptotic species richness estimator was used to predict the full complement of species present within each estuary that could be caught using seine netting. The rarefaction curves and species richness estimator enable the interrogation of two underlying paradigms of ecological species richness: the species-energy relationship and the species-area relationship. This analysis reveals distinct groups which show a significant relationship with latitude and size, although the size effect has a smaller influence. In particular, the species-latitude relationship paradigm holds true in this study while the species-area relationship paradigm only applies when latitude is considered concomitantly. Marine species in particular appear to account for the increased fish species number at lower latitudes. The underlying influence of latitude and estuary size suggests that any managerial tool that explores anthropogenic impacts (such as those used in the European Water Framework Directive) should include these aspects. It is concluded that the analysis gives environmental managers an objective cost-beneficial method of identifying when and where further sampling does not give further information for management.