Temporal variation in the behaviours of the honeyhead damsel Dischistodus prosopotaenia on an inshore reef

Territorial herbivorous (or 'farming') damselfish are ubiquitous on coral reefs and, through their defensive and farming behaviours, maintain algal assemblages within their territories that are distinct from adjacent areas. Whereas their influence on the composition of benthic communities and their defensive behaviours have been widely studied, comparatively little is known of their time allocation among different behaviours or how these patterns vary temporally. This study investigates the temporal variation (morning vs. afternoon; September vs. March) in the behaviours of the honeyhead damsel, Dischistodus prosopotaenia, on an inshore reef in the central Great Barrier Reef. Remote underwater video cameras were used to record the behaviours (farming/feeding, swimming, hovering and defending) of D. prosopotaenia in the absence of divers. D. prosopotaenia generally allocated the majority of their time to farming/feeding; however, the time allocation towards behaviours varied temporally. Individuals spent greater time farming/feeding in the afternoons (39.5%-59.3%) compared to the mornings (24.7%-42.3%). This pattern is consistent with the diel feeding hypothesis, whereby herbivorous fish feed at higher rates in the afternoon due to the greater nutritional quality of algae. The time spent farming/feeding was also positively related to the cover of turfs (primarily filamentous algae and cyanobacteria) within D. prosopotaenia territories. Interestingly, larger-bodied roving herbivorous fishes were among the least frequent fishes to enter D. prosopotaenia territories, yet they were the most frequently chased (46.7%) compared to omnivores (25.4%), planktivores (14.6%), carnivores (12.2%) and corallivores (9.4%). This likely reflects the ability of D. prosopotaenia to identify species with overlapping diets and alter their defensive response accordingly. These findings provide a more holistic appreciation of the behaviours of a farming damselfish and contribute to our understanding of their importance in coral reef processes.