The behavioral ecology of three Indian Ocean surgeonfishes (Acanthurus lineatus,A. leucosternon and Zebrasoma scopas): their feeding strategies,and social and mating systems

Synopsis The relationship between the morphology, feeding strategies and social and mating systems of three surgeonfishes was investigated. Adults of each defend feeding territories, intra-and interspecifically. The largest species, because of its morphological limitation, relies on food that has to be defended against many other species. It forms large colonies in which fishes singly defend small territories containing high standing crop algal mats. Colony formation is a mechanism by which the efficiency and effectiveness of interspecific territory defense is increased. The smallest species, because of its morphological adaptations, is able to rely most on food that other species cannot efficiently exploit. It forms pairs that defend large territories containing a thin algal mat. It is restricted to the poorest quality habitat by the aggressive activities of more dominant species. The third species, which also forms pairs, has an intermediate feeding strategy. The local coexistence of these three and other surgeonfishes results from a combination of (i) their partitioning both habitat and food resources, and (ii) the populations of two of the most dominant species apparently being below the carrying capacity. Territoriality and the absence of parental care facilitates pair formation in surgeonfishes. Permanently territorial species usually form pairs. The colonial species does not form pairs because the colonial habit facilitates interference of males in each other's spawnings.