Growth of mussels (Mytilus edulis galloprovincialis) on cultivation rafts: Influence of seed source, cultivation site and phytoplankton availability

Mussel seed, obtained from the intertidal zone; and permanently immersed collector ropes, was cultivated on ropes suspended from three rafts located at three different sites within the Ria de Arousa (Galicia, NW Spain), Sites were characterized by different levels of phytoplankton availability. The source of seed stock had a marked influence upon subsequent mussel growth; seed originating from collector ropes had higher growth rates than seed collected from intertidal areas and was probably due to the higher condition index and previous adaptation to rope culture conditions (permanent immersion) for these samples. Cultivation site also affected mussel growth; differences in chlorophyll a content and water current speed, which influence phytoplankton availabilty, were the major factors underlying variation in growth rate and condition index. It is recommended that seed obtained from collector ropes should be used in the commercial exploitation of this species, since it would shorten the total duration of the cultivation process by more than 10%.