Is the amount of algae related to territorial defense and reproductive success in the beaugregory damselfish?

Abstract

The species and quantity of algae growing in the territories of male beaugregory damselfish (Stegastes leucostictus) were compared to the defenders’ aggression and relative reproductive success. To offset major habitat differences among territories, males were given identical artificial breeding sites in January 1982. The amount of algae growing on the sites, the defense levels against common intruding species of fish, and the males’ reproductive success were assessed during the summer of 1982. The intensity of a defender's territorial defense was estimated by the frequency of his attacks against a fish housed in a clear jar placed within his territory. The total amount of algae was significantly correlated with estimates of reproductive success, and also with its territorial defense against one of the three fish tested (the herbivorous striped parrotfish, Scarus iserti, not the bluehead wrasse, Thalassoma bifasciatum, and the conspecific male). In addition to the effects of total algal biomass, effects of individual species were tested. Eight species of algae (out of the 20 found) made up 95.7% of the biomass, and only four of these species accounted for all significant correlations. Amphiroa sp. was positively correlated while blue‐green algae was negatively correlated with the defenders’ reproductive success. Four species of algae were correlated with the defender's attack intensity against the striped parrotfish, three positively (Digenia, blue‐green, and Laurencia) and one negatively (Amphiroa sp.). No significant correlations with defense against the two other fish tested were found for either total algal biomass or individual algal species.