Settlement and recruitment pattern variability of the mussel Mytilus galloprovincialis Lmk. from SE Bay of Biscay (Basque Country)

Abstract

The annual settlement and recruitment patterns of Mytilus galloprovincialis Lmk. were assessed using collector ropes deployed at five sites along the Basque coast inhabited by wild mussel populations. The study was carried out over two periods of ten months each in three estuarine and two coastal sites, and enabled the discovery of a potential relationship between observed primary settlement and the spawning period of wild mussel populations, shedding light on the recruitment of these populations. Primary settlers were present throughout the year with highest abundances from early summer to fall. A spatial settlement pattern was also observed, with eastern estuaries showing higher settlement rates than western ones and coastal sites showing intermediate settlement rates. These spatial and temporal settlement variations could be partially explained by seasonal fluctuations in environmental factors, such as temperature and nutrients, as well as by spawning differences observed at these estuarine and coastal sites. Some inter-annual variability of settlement and recruitment was observed, with higher settlement rates in the second studied year. This inter-annual variability was consistent with the inter-annual variability of the environmental factors. The recruitment of juvenile mussels was shown to be more determined by post-settlement processes than by initial settlement abundance. Indeed, there was a substantial loss of post-larvae during fall and winter, which was due to these post-settlement processes. Thus, it is advised that ropes, which were deployed in spring and collected in winter, to be collected earlier to avoid such losses. Little space is available (i.e., due to user conflict) on the Basque Coast. Despite these limitations, these sites, particularly Bidasoa estuary, could be suitable for future seed gathering for the mussel aquaculture industry in the Basque Country. (C) 2019 Elsevier B.V. All rights reserved.