Coral reef fishes exploit flow refuges in high-flow habitats

Abstract

Behaviour can offset the limitations of the morphology and physiology of a species to profoundly influence patterns of resource use. In fishes, flow refuging is a behavioural mechanism that may facilitate the occupation of turbulent, high-flow habitats by reducing extreme environmental demands on their swimming capabilities. Using a novel combination of experimental and field techniques, we examined the refuging patterns of coral reef fishes to demonstrate the potential energetic advantages of flow refuging on coral reefs. Field evaluations of 3 common reef flat species (Halichoeres margaritaceus, Pomacentrus chrysurus and Chrysiptera brownriggi) revealed clear species-specific refuge selectively towards substratum holes and coral heads, with all species using these 2 refuge types in a manner that provided significant shelter from ambient flow. Indeed, at experimental flow speeds similar to those in the field (10 to 90 cm s-1), measurements taken in and around replicas of these refuges identified flow reductions of 60 to 100% depending on ambient flow speed, type and size of the refuge. In addition, the degree of refuging displayed by these reef fishes appeared to be strongly linked with swimming ability, with smaller individuals and slower-swimming species refuging more frequently than individuals with stronger swimming abilities (i.e. refuging frequency in P. chrysurus > C. brownriggi > H. margaritaceus). Ultimately, it appears that refuging is not just a predator-avoidance mechanism, but also enhances the ability of coral reef fishes to sustain themselves in high-flow environments, which may underpin their occupation of otherwise inhospitable wave-swept habitats.