Food selection by the Canbbean stoplight parrotfish Spansoma vlrlde was lnvestlgated on a fnnging coral reef of Bonalre, Netherlands Antllles For different reef zones, the diet composition for each life phase was determined by descnption of randomly selected bites, and compared to the avallabllity of food resources, as determined w~t h the aid of chaln-llnk transects S viride employs an excavating grazing mode and feeds almost exclus~vely on algae associated with dead coral substrates Preferred

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... food types are large and sparse turfs growlng on carbonate substrates inhabited by endohthic algae Crustose corallines, with or without algal turfs are not preferred Feeding forays were longer on the preferred food types Foraging preferences are related to nutntlonal quahty of the food types and their yleld, i e the amounts of blomass, proteln and energy that can be Ingested per bite, as calculated from the size of grazing scars and the biochemical composition of the algae In spite of selective forag-Ing, a large proportion of b~t e s is taken on infenor food types Endolithic algae constitute an Important food resource for scraping herbivores, such as S vlnde These algae have relatively hlgh energetic value, and allow a high yield as a result of weakening the carbonate matrix by thelr boring filaments The yield of algal resources also depends on the skeletal density of the limestone substrates On deeper reef parts ( > 3 5 m depth), low-density substrates predomnate, resulting in higher y~e l d s of algae per bite than are attalned from high-denslty substrates that predominate on shallower reef parts The increased availablllty of hlgh-yleld food and substrate types coinc~des w~t h the occurrence of harermc terrltorlal behavlour m S v i r~d e males on the deeper reef parts Terntones are defended agalnst conspeclflcs and have a n Important function as spawning sites It 1s argued that the access to supenor food resources on the deeper reef makes terntonal defence feaslble for S viride