Ecology of threespot damselfish: Social organization, age structure, and population stability

Abstract

The threespot damselfish, Eupomacentrus planifrons Cuvier, population in the back reef of Discovery Bay, Jamaica was found to be positively correlated with the size of Acropora cervicornis Lamarck patches. Densities of these damselfish, however, were negatively correlated with patch size indicating an intraspecific territorial spacing mechanism on larger patches with contiguous territories. Male threespots competitively exclude smaller males and dusky damselfish from A. cervicornis patches, while female threespots preferentially select Montastrea annularis (Ellis and Solander) heads for territory sites. Four age classes of threespot damselfish were evident from dissection of individuals. Breeding was on a year-round lunar cycle with females laying clutches within male territories. Experimental removals of threespots indicated that replacements within 48 h were in a hierarchical order: (1) replacements from a non-breeding pool of wanderers, (2) replacements by resident damselfish abandoning their territories, and (3) replacements by dusky and immature threespot damselfish. Reduced aggression and cooperative behavior by threespots withinlarge coral patches imparted a high degree of persistence stability to the population with adjustment stability being from replacement of threespots from the pool of wanderers.