MEPS 606:39-53 (2018)  -  DOI: https://doi.org/10.3354/meps12782

ABSTRACT: Settlement is a complex biological process that, for most species, marks the end of pelagic larval life and the beginning of benthic life, and is therefore critical for the replenishment and persistence of marine benthic populations. Increasing evidence points to the surf zone as an important last hurdle modulating successful onshore larval settlement in intertidal and shallow subtidal habitats. Wave hydrodynamics cause the development of near-bottom flows, which have been suggested as a mechanism of cross-surf zone transport of heavy sinking competent larvae of mussels. Here, we tested the generality of this model with new data, contrasting 2 distant (100 km) sites with different surf zone configurations and slopes. Daily mussel settlement rates were measured for 3 periods of 10 d over 3 different settlement seasons between 2015 and 2017, and were related to potential cross-shore transport mechanisms. When corrected for differences in surf zone slope between sites and de-seasoned, near-bed bottom flows explained 87% of the variance in daily settlement at both sites, with the exception of the steep surf zone site in 2016, when settlement increased even faster with the flow. When flow direction is considered, site-specific alongshore and cross-shore transport patterns emerge at the reflective and dissipative shores, respectively. These patterns suggest that wave-induced transport through the surf zone can be a general mechanism favoring onshore mussel settlement, and highlight the importance of local topography in modulating such transport mechanisms.

KEY WORDS: Larval supply · Orbital velocities · Coastal orientation · Upwelling