The trophic status of 3 territorial damselfishes, Stegastes nigricans, Hemiglyphidodon plagjometopon and Dischjstodus 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 pm, 125-500 pm and >500 pm. Each fraction was examined to determine its composition (detritus, sediment, algae, invertebrate), dry mass, organic matter

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... tent and C:N ratio. The detritus-dominated 10-125 pm fractions were found to contaln approximately half of the organic matter in territory samples (46 to 60%) and had C : N ratios s~rnilal-to the algal fractions. In all 3 species the 10-125 pm fract~on was ingested in proportion to its ava~labll~ty In contrast, invertebrates, algae and sediment (>500 pm) were under-represented in the diet. It is suggested that the detritus-dominated 10-125 pm terntory fractlon 1s the primary source of organlc material and nltrogen for all 3 species. Terntonal~ty by damselflshes may be related to detrital production and accumulation rather than algal growth.