Utilization of mangrove crab-burrow micro-habitats by the goby Redigobius dewaali: Evidence for dominance hierarchy

When a range of life-history groups within a population exploit similar niches, hierarchies are often established whereby optimal resources are capitalized by dominant individuals. The present study investigates the feeding and movement of a size structured population of gobies residing in crab burrow micro-habitats, within this context. All life-history stages of the goby Redigobius dewaali were found to utilize burrow-pools formed by the crab Scylla serrata in the mangrove intertidal zone of an estuary at low tide. Gut content analysis was therefore conducted to test for feeding overlap and potential intraspecific competition among various sizes of fish residing in these habitats. In addition, an exclosure experiment was conducted to determine whether these fish leave the burrow-pools at high tide to forage over the intertidal flats. While ontogenetic dietary shifts across size-classes occurred, copepods and amphipods comprised the most important components of the diet for most size-classes, resulting in a large degree of dietary overlap. Of the adult R. dewaali sampled from pools, a single large mature male was sampled from each burrow, suggesting territoriality, a trait well observed in males of many goby species. The experimental component of the study highlighted the movement of smaller individuals, but not larger individuals, from the burrow-pools at high tide. As all life-history stages occur in the same microhabitats, and forage on much of the same prey, we suggest that the existence of a competitive hierarchy resulted in the need for the smaller individuals to find alternate feeding areas, consistent with dominance hierarchy theory. •Redigobius dewaali inhabit burrows of Scylla serrata in mangrove intertidal flats.•Feeding and movement of gobies from these micro-habitats were evaluated.•A large degree of dietary overlap was found across R. dewaali size-classes.•Smaller gobies move from burrow-pools at high tide while mature adults remain.•These findings are consistent with dominance hierarchy theory predictions.