Abstract
The application of high-resolution genetic data has revealed that oceanographic connectivity in marine species with planktonic larvae can be surprisingly limited, even in the absence of major barriers to dispersal. Australia’s southern coast represents a particularly interesting system for studying planktonic larval dispersal, as the hydrodynamic regime of the wide continental shelf has potential to facilitate onshore retention of larvae. We used a seascape genetics approach (the joint analysis of genetic data and oceanographic connectivity simulations) to assess population genetic structure and self-recruitment in a broadcast-spawning marine gastropod that exists as a single meta-population throughout its temperate Australian range. Levels of self-recruitment were surprisingly high, and oceanographic connectivity simulations indicated that this was a result of low-velocity nearshore currents promoting the retention of planktonic larvae in the vicinity of natal sites. Even though the model applied here is comparatively simple and assumes that the dispersal of planktonic larvae is passive, we find that oceanography alone is sufficient to explain the high levels of genetic structure and self-recruitment. Our study contributes to growing evidence that sophisticated larval behaviour is not a prerequisite for larval retention in the nearshore region in planktonic-developing species.
Highlights
Many coastal marine species have a two-phase life-cycle in which adults are sessile or sedentary, with dispersal instead facilitated by pelagic propagules such as eggs and planktonic larvae[1,2]
Seascape genetics has proven to be powerful in helping to identify factors that limit connectivity in the oceans[11,18,19]
All loci were considered suitable for inclusion in population genetic analyses
Summary
Many coastal marine species have a two-phase life-cycle in which adults are sessile or sedentary, with dispersal instead facilitated by pelagic propagules such as eggs and planktonic larvae[1,2]. The study species, Siphonaria diemenensis (Quoy & Gaimard, 1833) is a common rocky shore limpet that occurs throughout southern and eastern temperate Australia[20] It has a high fecundity[21] and a planktonic larval dispersal phase[22], and unlike many other coastal invertebrates, it is not genetically subdivided into regional genetic units whose ranges are linked to the region’s biogeographic provinces[23,24]. Southern Australia is dominated by three ocean currents (the Leeuwin Current, the South Australian Current and the Zeehan Current), which together can potentially connect the region’s entire fauna over a distance > 5000 km[25], realised dispersal is often surprisingly limited[10,11]. We identify high levels of self-recruitment, and demonstrate that near-shore oceanographic constraints play key roles in limiting the spread of passively-dispersing particles
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