1. To the non-specialist, problems are often associated with the quantification of sponge species diversity, as colour, shape and size can be highly variable within a single species. These variables can lead to an under-estimation of the contribution of sponges to the biodiversity of the benthos especially during biological surveys.
2. Sponge species diversity (Shannon H′ values), richness (mean number of species) and morphological diversity (Shannon H′ values) were sampled at six sites (6 m depth intervals) on vertical (90°) and inclined surfaces (45°) experiencing different flow regimes at Lough Hyne Marine Nature Reserve (Ireland). Morphological diversity was sampled independently of species diversity. The time taken for the collection of both species and morphological diversity was recorded.
3. Morphological diversity was positively correlated with both sponge species diversity (r2=0.87, p<0.05) and sponge species richness (r2=0.70, p<0.05). Linear regression was found to be significant for both the relationships (p<0.05 for each F-value). A sigmoidal relationship (r2=0.97, p<0.05) was found between morphological and species richness which proved to be significant (F-value 40.67, p<0.05). Separate Bray–Curtis dendrograms and correspondence analysis of morphological and species community compositions at the six sites showed very similar clustering and four major clusters were identified.
4. The results of the present study indicate that sampling of sponge morphological diversity, rather than sponge species diversity and richness may be used as a qualitative estimate of sponge species diversity. Sampling of morphological diversity is much less time consuming, both in the field and laboratory, than collecting species diversity data and no specialist knowledge is required. Consideration is given to the use of such relationships in biological surveys and bio-monitoring. Copyright © 2001 John Wiley & Sons, Ltd.