Utilization of mangrove crab-burrow micro-habitats by the goby Redigobius dewaali: Evidence for dominance hierarchy R. Kramer a , C.D. McQuaid a , T.J.F. Vink b , B.P. Mostert a , R.J. Wasserman a, ⁎ a Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Grahamstown 6140, South Africa b Department of Botany, Coastal and Marine Research Unit, Nelson Mandela Metropolitan University, P O Box 77000, Port Elizabeth 6031, South Africa abstract article info Article history: Received 4 August 2014 Received in revised form 7 October 2014 Accepted 9 October 2014 Available online 23 October 2014 Keywords: Estuary Gobiidae Niche overlap Ontogeny Scylla serrata burrows Size-class 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 con- text. 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 con- ducted 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 micro- habitats, 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. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The facultative and obligatory utilization of estuaries as nursery and refuge areas by various fish species is well recognized, with much research having been conducted on coarse-scale estuarine utilization by ichthyofauna (Rountree and Able, 2007; Wasserman et al., 2010; Weinstein and Brooks, 1983). There is however, limited information pertaining to the small scale movement, utilization of micro-habitats, and feeding ecology of many of the fish species exploiting these environments, particularly within the context of ontogeny (Morrison et al., 2002; Wasserman, 2012; Wasserman and Mostert, 2014). In this regard, the present study expands on work conducted by Wasserman and Mostert (2014), in which burrows of the Estuarine Mud Crab (Scylla serrata, Forksal), in a mangrove estuary, were found to form micro-habitats extensively used by a specific gobiid. In their study, Wasserman and Mostert (2014) sampled numerous intertidal S. serrata burrows at low tide, when the burrows were isolated from the main estuary channel, creating pool-like habitats in the intertidal mangrove flats. They found large numbers of a single goby species, the Checked Goby (Redigobius dewaali, Weber, 1987), dwelling in all sampled burrows. The burrow dwelling R. dewaali populations comprised a range of life-history stages, from adult to post-flexion larvae, with the vast majority belonging to the early life-history stages (Wasserman and Mostert, 2014). Competition theory asserts that when population densities expand to the point where resources become limited, antagonistic interactions reduce the success of individuals (Bolnick, 2004). One way in which this is observed is through the establishment of dominance hierarchies within a population. Individuals within a population are often an assem- blage of heterogeneous units that are not ecologically equal, differing in life-history stage, body size and competitive abilities (Polis, 1988; Wilbur, 1980; Wissinger, 1992). Dominance hierarchy theory predicts that when a range of life-history groups of a given population exploit similar niches, dominance will ensue (Werner and Gilliam, 1984). In this way, subordinate groups can be forced to occupy broader home ranges than dominant individuals, who capitalize on smaller easily- defendable territories that offer superior foraging opportunities (Buchheim and Hixon, 1992; Chase et al., 1994). Within this context, we investigate the diet and movement of various size-classes of R. dewaali that reside within S. serrata burrow microhabitats. We Journal of Experimental Marine Biology and Ecology 462 (2015) 1–7 ⁎ Corresponding author. E-mail address: ryanwas21@gmail.com (R.J. Wasserman). http://dx.doi.org/10.1016/j.jembe.2014.10.012 0022-0981/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe