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 characterist ics in the Ria de Vigo (NW Spain). Larvae were more abundant in plankt on samples (20 x 10(3) larvae m(-3)) taken near mussel culture rafts t han 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 wa ter temperature (spring to summer). Post-larvae were found in plankton from the intertidal mussel beds, from late summer to early autumn, sp ecially in the intertidal zone of exposed rocky shores (1.2 x 10(3) m( -3)). Post-larvae were occasionally found in plankton samples taken ne ar mussel rafts (< 10(2)/m(3)). in the intertidal mussel beds, post-la rvae sizes reached 2.1 mm, while the maximum size found in the vicinit y of mussel rafts was of 1 mm. The low number, and even absence, of po st-larvae in plankton samples taken near the surface from localities a way 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.