Functional diversity: a study on the Bay of Biscay nursery habitats

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Grouping species according to their biological (i.e. morphological, behavioural, and physiological) traits represents a decisive step in assessing the functional diversity of a community. As functional diversity represents a good measure of ecosystem resilience and resistance, it is thought that groups of functional traits may thus be use to develop indicators to assess community responses to natural and human perturbations. The present study aims at (i) testing the use of groups of functional traits as an alternative to the taxonomic-based approach to develop indicators of nursery states, and (ii) assessing the relationship between species and functional diversity to measure the functional redundancy in nursery fish communities. Groups of functional traits were determined at six coastal nurseries located in the Bay of Biscay. This was done using a methodological framework based on a three-matrix approach (species*sites, species*traits, sites*environment) allowing direct assessment of the relationship between groups of functional traits and the environment. Functional diversity was estimated using a recently developed continuous index. Analyses conducted on data collected yearly between 2000 and 2003 indicated differences in the number and composition of functional groups of traits across the nurseries. Nurseries showing higher number of functional traits were not the ones with higher measures of functional diversity. These results, together with the ones from the redundancy analyses, suggest that locally complex interactions between species identity and functional roles govern the nurseries of Bay of Biscay. Complementary analyses are however needed to advance our understanding and to investigate whether the observed differences in functional diversity among the nurseries may be anthropogenic or due to natural variability.