Group Dynamics and Interactions between Two

This paper examines the relationship between Dascyllus aruanus and Pomacentrus moluccensis, two species of damselfish which commonly form mixed colonies on the reef flat of Heron Island, in Australia’s Great Barrier Reef. D. aruanus, commonly known as the Humbug Damselfish, has been extensively studied. They defend their territory (consisting of branched coral) and form both conspecific and bispecific groups, cohabiting with a range of other similar damselfish species1,3,8. These groups include a range of fish sizes in a strict hierarchy led by a single dominant male of either species2. P. moluccensis has not been studied as thoroughly but has been shown to form groups with Humbugs and shares many of their characteristics1,9. To investigate the relationship between these species, 25 coral heads supporting bispecific and conspecific fish colonies were measured and the fish were counted and placed within size categories. The data revealed no significant correlation between coral size and group size, indicating an adequate resource supply. There was also a differential distribution of fish sizes found for each species, suggesting different ecological dynamics. The results suggest that the two species preferentially live together, with the dominant adult in each group equally likely to be of either species. This project raises a number of further questions and requires elaboration with a larger sample size and minimization of bias.