Mar Biol (2010) 157:945–953 DOI 10.1007/s00227-009-1375-y 123 ORIGINAL PAPER Genetic structure across the GBR: evidence from short-lived gobies Claire A. Farnsworth · David R. Bellwood · Lynne van Herwerden Received: 15 December 2008 / Accepted: 11 December 2009 / Published online: 29 December 2009  Springer-Verlag 2009 Abstract The Great Barrier Reef (GBR) exhibits distinct cross-shelf zonation. These patterns are particularly well documented in reef Wshes and have been attributed to either environmental gradients (e.g. wave energy, oceanography) or barriers to gene Xow. This study examined the extent to which barriers to gene Xow contribute to cross-shelf patterns by examining the mitochondrial DNA of gobies (genus Eviota). The genus Eviota was selected due to its extreme life history characteristics (shortest vertebrate life- span) and cross-shelf distribution patterns (E. queenslan- dica, inner- and mid-shelf, and E. albolineata mid- and outer-shelf). Although cross-shelf barriers to gene Xow were predicted, this study found no population structure between shelf locations. However, a genetically distinct population of E. queenslandica (the inner-shelf species) was observed at North Direction Island (Phi st = 0.088, P = 0.004). As no comparable structure was observed in E. albolineata (the outer-shelf species) it may be that habitat type (E. queenslandica = reef lagoon, E. albolineata = reef crest) is a signiWcant factor driving the structure observed in E. queenslandica. Larval behaviour, olfactory or audi- tory senses and reef selection at settlement could be assist- ing larvae to return to reefs similar to natal reefs. We suggest that ecological gradients are more important than barriers to gene Xow in structuring cross-shelf distributions within Eviota. Introduction Several studies of population dynamics in reef environ- ments have uncovered small-scale genetic divisions, for example in blennioid Wshes (Riginos and Nachman 2001; Riginos and Victor 2001), stomatopods (Barber et al. 2002), gobies (Taylor and Hellberg 2003) and snapper (Ovenden et al. 2004). It appears that small-scale genetic subdivisions are possible even in the apparently highly con- nected marine environment. On the Great Barrier Reef (GBR), it may be hypothesised that the strongest divisions will be observed across the reef shelf as this displays one of the clearest biogeographic patterns. There is distinct zona- tion in coral reef systems as one moves away from the coast. Such cross-shelf patterns have been described for a wide range of organisms including algae (Wismer et al. 2009), corals (Done 1982; Dinesen 1983), sponges (Wilkinson and Ceshire 1989), crustaceans (Preston and Doherty 1994) and reef Wshes (e.g. Russ 1984; Bellwood and Wainwright 2001; Kingsford and Hughes 2005). These patterns appear to extend along the entire length of the GBR, stretching over 2,000 km and 12 degrees of latitude (Williams 1983). Such cross-shelf zonation is not unique to the GBR. Similar patterns have been recorded in the PaciWc Communicated by T. Reusch. Electronic supplementary material The online version of this article (doi:10.1007/s00227-009-1375-y) contains supplementary material, which is available to authorized users. C. A. Farnsworth · D. R. Bellwood (&) · L. van Herwerden School of Marine and Tropical Biology, James Cook University, Townsville, QLD 4811, Australia e-mail: david.bellwood@jcu.edu.au C. A. Farnsworth · L. van Herwerden Molecular Evolution and Ecology Laboratory, James Cook University, Townsville, QLD 4811, Australia D. R. Bellwood Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia