Cryptic dietary components of territorial damselfishes (Pomacentridae, Labroidei)

The trophic status of 3 territorial damselfishes, Stegastes nigricans, Hemiglyphidodon plagiometopon and Dischistodus perspicillatus, was examined by comparing the resources available in territory epilithic algal communities (EACs) with gut contents. Samples were divided into epilithic algae and associated material in 3 size fractions: 10-125 mu m, 125-500 mu m and >500 mu m. Each fraction was examined to determine its composition (detritus, sediment, algae, invertebrate), dry mass, organic matter content and C:N ratio. The detritus-dominated 10-125 pm fractions were found to contain approximately half of the organic matter in territory samples (46 to 60%) and had C:N ratios similar to the algal fractions. In all 3 species the 10-125 mu m fraction was ingested in proportion to its availability. In contrast, invertebrates, algae and sediment (>500 mu m) were under-represented in the diet. It is suggested that the detritus-dominated 10-125 pm territory fraction is the primary source of organic material and nitrogen for all 3 species. Territoriality by damselfishes may be related to detrital production and accumulation rather than algal growth.