Modelling sponge species diversity using a morphological predictor: a tropical test of a temperate model

The contribution of sponges to marine surveys is often underestimated due to problems of identification, synonymous species and limited numbers of specialists in the field. Bell & Barnes (2001) illustrated how sponge morphological diversity (diversity of body forms) might be used as a predictor of sponge species diversity and richness. This study investigated these relationships at six tropical West Indian Ocean localities in a number of habitat types. These habitats included tropical coral reefs, soft substratum (seagrass, mangrove and sand), caves and boulders. Sampling was undertaken at three depth zones in coral reef habitats only (intertidal, 10–15 m and 20–25 m), with the other habitats sampled in less than 10m of water. Species diversity and richness were significantly correlated (P < 0.05) with morphological diversity at all localities and depths in coral reef and soft substratum habitats. However, no significant correlation was found between these variables in cave or boulder habitats. The slope of the linear regression found between morphological diversity and species diversity did not significantly differ between coral reef, soft substratum and temperate reef (data taken from Bell & Barnes 2001) habitats. Similarly coral reefs showed the same relationship between morphological diversity and species richness as temperate reefs, however the relationship between morphological diversity and species richness was significantly different at both habitats compared with soft substratum environments. Sponge morphological diversity therefore may be more useful as a predictor of sponge species diversity, rather than species richness, as the former relationship is common between more habitats than the latter.