Are indicator groups and cross-taxon congruence useful for predicting biodiversity in aquatic ecosystems?

Resources for biodiversity surveys and conservation planning are limited, and conservation biologists and environmental managers are thus striving to find suitable surrogates for mapping and predicting biodiversity. Among popular surrogates are indicator groups that could be used for predicting variation in the biodiversity of other taxonomic groups. Despite some success at large scales, surveys of multiple taxonomic groups across ecosystems have suggested that no single group can be used effectively to predict variation in the biodiversity of other taxonomic groups. This paper concentrates on indicator groups and cross-taxon congruence in species richness and assemblage composition patterns in inland aquatic ecosystems. As has been found in studies of terrestrial ecosystems, there is low utility for indicator groups in predicting the biodiversity of other taxa in aquatic ecosystems. Even when statistically highly significant correlations between taxonomic groups have been detected, these correlations have been too weak to provide reliable predictions of biodiversity among various taxonomic groups or biodiversity in general. Indicator groups and, more generally, cross-taxon congruence thus do not appear to be particularly relevant for conservation in the freshwater realm.