Modification of benthic communities by territorial damselfish: a multi-species comparison

The effects of territorial damselfish on coral reef benthos have been well-studied for a few relatively large-bodied species with visually distinct territories. Despite a growing body of research demonstrating their abundance, and their effects on algae, corals and other grazers, there has been little research on the effects of the territorial damselfish community as a whole. This study investigated the space occupation, territory composition, and diet of ten damselfish species at three locations: Magnetic and Orpheus Islands (Great Barrier Reef), and Kimbe Bay (Papua New Guinea). Territories were measured, and the composition of benthic communities inside and outside territories was assessed both in situ and from algal collections. The stomach contents of territorial damselfishes were also quantified. Although the larger, previously well-studied species had the most visible effect on the benthic community in their territories, all the smaller species also significantly affected the algal composition, normally with an increase of palatable algae. However, the composition of algal assemblages inside the territories of different species varied considerably. Damselfish territories were highly individual, not just among species, but also among locations. Diets were diverse and indicated a greater degree of omnivory and detritivory than previously thought. At all locations, territories occupied a substantial proportion of the substratum: > 25% on Magnetic Island, > 50% at Orpheus Island, and similar to 50% in Kimbe Bay. Within individual zones, this figure was as high as 70%. The contribution of territorial damselfishes to a range of benthic patterns and processes is considerable, and future benthic studies may need to distinguish more closely between territory and non-territory areas.