Trophic ecology of the damselfish Amblyglyphidodon curacao (Pomacentridae)

Abstract Planktivorous damselfish (family Pomacentridae) are among the most conspicuous and abundant fishes on coral reefs. Although planktivores often drive coral reef productivity by providing pelagic subsidies, the trophic ecology of many planktivorous damselfish remains poorly understood. Here we investigate the trophic ecology of Amblyglyphidodon curacao (Bloch, 1787), a planktivorous damselfish common throughout the Indo-Pacific. This study combined extensive stomach contents analysis and behavioural observations from sheltered and exposed sites at two locations along Australia's Great Barrier Reef. A. curacao were found to be highly omnivorous, feeding on a diverse range of zooplankton, pelagic cyanobacteria, and benthic algae. Pelagic taxa predominated the diet, especially Trichodesmium spp. (henceforth Trichodesmium ), which formed a significant portion of the diet and was consumed by almost all individuals. Trichodesmium has few known consumers, and its consumption, at some times of the year, by coral reef fish represents a novel trophic link. Furthermore, diets were varied over broad spatial scales, and differences were detected between sheltered and exposed sites; a greater diversity of prey were consumed in exposed sites at both locations. Behaviourally, A. curacao were found to be highly sedentary; movement was on a scale of metres and was unaffected by individual body size, time of day, or tidal phase. Conversely, foraging rates varied with fish size, current speed, and tidal phase. Smaller individuals (2.5—4.5 cm SL) had higher foraging rates than larger individuals (> 4.5 cm SL) and the foraging rates of all individuals increased with current speed. The foraging rates of large individuals were reduced during low tide but were unaffected by time of day. These results categorise A. curacao as a highly opportunistic, omnivorous, and sedentary damselfish that feeds on prey delivered by currents and establishes a novel trophic link between coral reefs and the pelagic realm. Further, the broad range of prey taxa from pelagic and benthic sources suggests that A. curacao is resilient to variation in food supply among multiple reef zones.