Larval dispersal of intertidal organisms and the influence of coastline geography

The dispersal stages of organisms with sessile adults must be able to select habitats with suitable conditions for establishment and survival, and must also be able to reach those locations. For marine planktonic larvae, movement due to currents is often orders of magnitude greater than movement due to swimming behaviour, so transport is largely passive. Current patterns are determined by the interaction of geography with tidal forces, modified by meteorological conditions. These linkages impose an area-specific focus to connectivity studies. Yet, how geographical features and meteorological forcing combine to produce specific current patterns and resultant connectivity among populations remains unclear. In this study, we aimed to understand marine larval connectivity as a function of coastal topography, and considered dispersal from equally spaced coastal sites in a complex fjordic region. We studied a range of larval durations (1-28 days), and two different but typical meteorological forcing scenarios. Larvae released from regions of high current velocity, open coastline and low local habitat availability travelled furthest but were less likely to disperse successfully. Extensive natal habitat in the vicinity of a site generally had a positive impact on the number of larvae arriving, as did low current velocities. However, relationships between numbers of arriving larvae and local geographical indices were complex, particularly at longer larval durations. Local geography alone explained up to 50% of the variance in success of larvae released and around 10% of the variation in the number of larvae arriving at each site, but coastline properties fall short of predicting dispersal measures for particular locations. The study shows that meteorological variation and broad scale current patterns interact strongly with local geography to determine connectivity in coastal areas.