Larval dispersal and population connectivity: implications for offshore renewable energy structures
The installation of marine renewable energy devices (MREDs) is progressing rapidly along many coastlines. It has been suggested that MRED arrays could provide stepping-stones for larval dispersal, mediating species range expansions or invasions. As common members of hard-substrate fouling communities and likely colonisers of MREDs, the larval dispersal processes of barnacles (Cirripedia: Thoracia) in the Firth of Lorn (Scotland) are assessed at scales ranging from mm to 10s ¿ 100s km. At the scale of the organism itself, significant differences in larval mass densities and sinking velocities were observed between species of cirripedes, suggesting that larval physiology and morphology play an important role in water column vertical positioning. The importance of vertical positioning to horizontal transport and dispersal of larvae was identified in field surveys of the horizontal and vertical distributions of cirripede larvae, which revealed the interplay of wind-driven and tidally-oscillating currents in determining transport distances. Numerical simulations of larval dispersal based on a three-dimensional hydrodynamic model then demonstrated that larvae with shallower abundance distributions often experienced greater horizontal transport, but that net dispersal distances were often greater for larvae deeper in the water column. Overall, simulated transport and dispersal distances were greatest for particles released at habitats further from the coast, such as MREDs, suggesting that the connectivity of these adult populations may be enhanced. Together, larval morphology, vertical positioning, and the coastal proximity of adult habitat could serve as useful indicators of larvae capable of reaching nearby newly installed offshore structures. For locations designated for MRED development in the Firth of Lorn, it is suggested that species with dispersal abilities similar to the cirripedes in this study could feasibly use these structures as stepping-stones for dispersal and range expansion, which could have important consequences when fouling communities are comprised of commercially important or invasive species.
renewable energy, larvae, dispersal, cirripede
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