Individual differences in microhabitat use in a caribbean cleaning goby: a buffer effect in a marine species?

Abstract

Buffer effects occur when changes in population size result in the disproportionate use of poor‐quality sites or habitats. For species for which direct measurements of fitness differences between individuals are not possible, assessment of the temporal and spatial variations in patterns of habitat occupancy can therefore, shed light on the differences in quality between habitats and the individual fitness consequences of habitat choice. We provide the first evidence of the potential operation of a buffer effect for a site‐attached marine species. Caribbean cleaning gobies Elacatinus prochilos occupy coral and sponge substrata on fringing reefs in Barbados. Cleaning gobies at coral cleaning stations are frequently solitary or found in small groups, and spend 25 times longer cleaning than those on sponge. In contrast, sponge‐dwelling gobies exhibit highly stable, size‐structured dominance hierarchies in which, larger individuals are able to monopolize areas inside the sponge lumen with the highest abundance of the polychaete Haplosyllis spp, a favoured prey item. For adults, resource selection indices suggested a preference for sponge occupancy. As cleaning goby population size increased, however, the number of adult cleaning gobies occupying sponge substrata increased more rapidly than the number occupying coral habitat. Our results suggest that coral may be the preferred habitat, but in Barbados this habitat becomes saturated at very low population densities as a consequence of low client densities and ectoparasite loads. A larger proportion of the population, therefore, occupies sponge at most observed population densities. A population shift towards sponge rather than coral occupancy occurs between recruitment and maturity and may arise as a combination of differing survival of recruits and juveniles on coral and sponge and active movement of individuals towards sponge. Our results demonstrate that behavioural interactions are an integral part of population distribution and dynamics and are therefore, important in future studies of habitat choice and its associated fitness consequences.