The use of butterflyfishes (Chaetodontidae) as bio-indicators of habitat structure and human disturbance

The bio-indicator function of butterflyfish (Chaetodontidae) was investigat ed by studying habitat and disturbance effects on chaetodontid species in S ri Lanka. This was done by counting fish within 147, 50-meter belt-transect s in 3 different reef types including coral, sandstone and rock reefs; all of which contained a variety of habitats. Habitat distribution patterns for 36 species were observed. The relationships between habitat structure and butterflyfish assemblages were established in Spearman-rank correlations an d in multidi-mensional scaling ordinations, and the similarities in the two multivariate patterns of habitat and fish community composition were stati stically confirmed using the RELATE-procedure. Most species were restricted to a few habitats, however, the 3 most numerous species, Chaetodon decussa tus, C. trifascialis and C. trifasciatus had ubiquitous distributions, alth ough the two latter species dominated the coral-rich areas. Food availabili ty seemed to be an important factor influencing assemblage-specific distrib ution patterns. Coral-reef habitats had, in comparison with sandstone and r ock reefs, the most diversified and abundant butterflyfish community overal l. These habitats were dominated by corallivores, the overall most abundant trophic group, which showed strong positive correlations with live coral c over. Omnivores though, had more general preferences than corallivores occu rring in various habitat types. Habitat dependence was further confirmed by comparing coral reefs in sanctuaries with disturbed areas that had receive d extensive habitat destruction. The latter reefs had a more depauperate fa una with lower densities and diversity. Results from this study suggested t hat butterflyfish can act as indicators of habitat structure and disturbanc es in coral reefs in Sri Lanka. However, the butterflyfish bio-indicator hy pothesis has received ample criticism in a number of studies, and with the complexity characterizing tropical-reef ecosystems and the multitude of pro cesses structuring reef-fish communities, the global applicability of chaet odontids as bio-indicators is questionable.