Spatial patterns in abundance of a damselfish reflect availability of suitable habitat

For species with metapopulation structures, variation in abundance among pa tches can arise from variation in the input rate of colonists. For reef fis hes, variability in larval supply frequently is invoked as a major determin ant of spatial patterns. We examined the extent to which spatial variation in the amount of suitable habitat predicted variation in the abundance of t he damselfish Dascyllus aruanus, an abundant planktivore that occupies live , branched coral throughout the Indo-Pacific. Reef surveys established that size, branching structure and location (proximity to sand) of the coral co lonies together determined the "suitability" of microhabitats for different ontogenetic stages of D. aruanus. Once these criteria were known, patterns of habitat use were quantified within lagoons of five Pacific islands. Ava ilability of suitable habitat generally was an excellent predictor of densi ty, and patterns were qualitatively consistent at several spatial scales, i ncluding among different lagoons on the same island, among different island s and between the central (French Polynesia and Rarotonga) and western (Gre at Barrier Reef, Australia) South Pacific. A field experiment that varied t he amount of suitable coral among local plots indicated that habitat for se ttlers accounted for almost all of the spatial variation in the number of D . aruanus that settled at that location, suggesting that spatial patterns o f abundance can be established at settlement without spatial variation in l arval supply. Surveys of four other species of reef-associated fish reveale d that a substantial fraction of their spatial variation in density also wa s explained by availability of suitable reef habitat, suggesting that habit at may be a prevalent determinant of spatial patterns. The results undersco re the critical need to identify accurately the resource requirements of di fferent species and life stages when evaluating causes of spatial variation in abundance of reef fishes.