Distribution and abundance of mussel (Mytilus galloprovincialis Lmk) larvae and post-larvae in the Ria de Vigo (NW Spain)

To compare the presence and abundance of mussel larvae and post-larvae in offshore and inshore areas, plankton sampling was carried out over 18 months in four locations with different environmental characteristics in the Ria de Vigo (NW Spain). Larvae were more abundant in plankton samples (20 x 10(3) larvae m(-3)) taken near mussel culture rafts than in those from the intertidal mussel beds (1.6 x 10(3) larvae m(-3)). Increments in the abundance of larvae were closely related with the spawning periods of Mytilus galloprovincialis and with the rise in water temperature (spring to summer). Post-larvae were found in plankton from the intertidal mussel beds, from late summer to early autumn, specially in the intertidal zone of exposed rocky shores (1.2 x 10(3) m(-3)). Post-larvae were occasionally found in plankton samples taken near mussel rafts (< 10(2)/m(3)). in the intertidal mussel beds, post-larvae sizes reached 2.1 mm, while the maximum size found in the vicinity of mussel rafts was of 1 mm. The low number, and even absence, of post-larvae in plankton samples taken near the surface from localities away from the intertidal mussel bed could explain why previous studies disregarded the existence of a planktonic dispersion of post-larvae in this species. However, detailed studies on vertical distribution and daily (tidal) fluctuation of mussel planktonic stages are needed. (C) 1998 Elsevier Science B.V. All rights reserved.