Spatial patterns of larval settlement and early post-settlement survivorship of Mytilus galloprovincialis in a Galician Ría (NW Spain). Effect on recruitment success

Larval settlement and recruitment play an important role on the population dynamics of marine benthic invertebrates, and are key factors in the management of aquaculture industries. In order to check the current strategies of mussel seed gathering from collector ropes in the Ria of Ares-Betanzos (NW Spain), this work analyses the seasonal and spatial variability of larval settlement and recruitment of the mussel Mytilus galloprovincialis, as well as the relationship between settlement and recruitment. Our results highlight the importance of the hydrographic characteristics of the Ría de Ares-Betanzos on the spatial distribution of larval settlement and on the early post-settlement mortality, which determines recruitment success. The spatial distribution of larval settlement, with higher abundances in the northern-shore but significant larval retention in the southern culture areas, is in agreement with the positive subtidal circulation of this embayment and the larger residence times in the southern shore. The positive subtidal circulation of the Ría favours larval transport from the culture areas located in the south to the northern shore, while the larger residence times allow larval retention in the southern shore. The strong linear relationship between settlement and recruitment suggest density-independent mortality and allowed estimating recruitment abundances and short-term survival rates. The highest and lowest post-settlement mortalities were registered at the most external and sheltered locations respectively, suggesting that the vulnerability to the hydrodynamic stress may be the main cause of early post-settlement mortality of mussel juveniles on suspended substrates. Our results confirm that the sheltered culture polygons located in the inner area of the Ría of Ares-Betanzos are favourable environments for the recruitment of Mytilus galloprovincialis spat, supporting the current strategies of seed gathering from collector ropes in the Ría of Ares-Betanzos.