Molecular evidence supports coastal dispersal among estuaries for two benthic marine worm (Nephtyidae) species in southeastern Australia

Understanding patterns of dispersal of marine organisms among estuaries is important for the conservation of biodiversity and the design of marine park networks. Whereas numerous studies have recently assessed dispersal potential among key marine vertebrates and habitat-forming macroalgae, relatively few have assessed the potential for dispersal in ecologically important benthic polychaete worms. Here, we used phylogeographic analyses to test for evidence of genetic disjunctions among populations of polychaete worms from different estuaries in southeastern Australia. Our study focused on two species from the family Nephtyidae (Aglaophamus australiensis and Nephtys longipes) that are found intertidally in soft sediments in estuaries. Both species have planktonic larvae, but little is known about the survival times of the larvae, or their potential to disperse to other estuaries rather than settling locally. Genetic analyses of two mitochondrial (cytochrome c oxidase subunit I and 16S rDNA) markers in both species and a nuclear marker (28S rDNA) in A. australiensis were carried out to assess whether geographically distinct populations show genetic differences. Little evidence of genetic differentiation among populations was found, despite a high level of genetic diversity within each species. Although some significant population pairwise F-ST differences were detected for both species via AMOVA, these appeared largely driven by singleton haplotype diversity, whereas several common haplotypes were shared among all populations. Our results suggest that sedentary, benthic estuarine organisms with planktonic larvae can disperse to distant estuaries with the aid of tidal flushing and coastal ocean currents.