Taxonomic resolution needed to describe invertebrate assemblages and to detect harvesting effects on coral reef ecosystems

Due to the cost and time required for species identification, the taxonomic sufficiency approach has been developed in order to detect community response to a disturbance, using high taxonomic level without great loss of information. This concept has been widely applied to pollution monitoring studies but rarely to other forms of perturbations such as anthropogenic exploitation of marine resources. We applied this method both to soft-bottom (seagrasses) and hard-bottom (coralline) tropical invertebrate communities in New Caledonia, South Pacific. The objective was to test whether intermediate or high taxonomic levels (genus, family, class or phylum instead of species) are good descriptors of community patterns and changes in assemblages related to harvesting, by comparing harvested to non-harvested areas for the 2 habitats. We pooled species data into coarser taxonomic categories (from genus to phylum) and showed that matrices at different taxonomic resolutions were highly correlated, particularly for genus and family level for both habitats. Differences between harvested and non-harvested locations appeared to be clearly habitat-dependent; for soft habitats, genus and family resolution allowed the detection of changes between exploited and protected assemblages, while for hard habitats, the separation between harvested and non-harvested areas was less clear at high taxonomic level and required species-level identifications. These results suggest that the taxonomic sufficiency approach could be carefully applied to poorly known environments. Family level is a good descriptor of community composition for tropical reef invertebrates. Detecting changes due to anthropogenic exploitation requires different taxonomic resolutions depending on the considered habitat.