Interspecific Territoriality in a Pomacentrid Reef Fish, Pomacentrus Flavicauda Whitley.

Field observations on territorial behavior of the fish P. flavicauda were made for a total of 200 hours at Heron Island, Great Barrier Reef. Specimens 6 cm or more in length restricted their movements to areas of approximately 2 m over at least a 5-month period. Distribution of the fish was highly correlated (r = 0.89) with the amount of interface between sand and dead coral. Such areas provided algae in close proximity to shelter. Observations of agonistic behavior showed that P. flavicauda usually responded agonistically to 38 species of 12 families, but not to 16 other species of 6 families. Apparently competitors for algae elicit an agonistic response from P. flavicauda, while carnivores do not. Maps locating the positions of agosnistic encounters indicate that the entire home range is defended as a territory. The effectiveness of the agonistic behavior was indicated when, following the removal of 6 specimens of P. flavicauda, there was an increase in algal-feeding fishes seen within their territories. Implications, of these results for out understanding of interspecific territoriality are discussed.