Resource use and impact of three herbivorous damselfishes on coral reef communities

Abstract

Territorial damselfish are considered to be functionally important herbivores on coral reefs, promoting the abundance of preferred algae and depleting corals through a variety of ‘farming’ activities. However, the composition of algal and coral communities inside territories and patterns of feeding selectivity are known for only a few species. Here we compare substrata inside and next to territories of Plectroglyphidodon lacrymatus, P. dickii and Stegastes nigricans, 3 common damselfish in Papua New Guinea, and interpret patterns in relation to diets and patterns of feeding selectivity. The coral assemblages inside territories differed among fish species and also between defended and non-defended areas. Live corals dominated P. dickii territories, while those of P. lacrymatus and S. nigricans were primarily associated with algal substrata. Territories of P. lacrymatus were similar in coral composition to adjacent areas, while those of P. dickii and S. nigricans were associated with particular coral taxa. Territories of the 3 damselfish were similar in algal composition, with mixed turf algae (primarily blue-green algae Polysiphonia spp. and other filamentous red algae) more prominent inside territories and crustose coralline algae more prominent outside. Diets for the 3 species were also similar, as each species was primarily herbivorous and diets consisted of diatoms, blue-green algae, Polysiphonia spp. and other filamentous red algae. An experimental removal of P. lacrymatus showed that they promoted epiphyte loads without influencing macro-algal or coral cover. Our results suggest that while these 3 species of damselfish vary in their interactions with coral reef habitat, they selectively cultivate a similar range of epiphytic food algae on different substrata.