Larval and post-larval vertical distribution of the mussel Mytilus edulis in the White Sea

The vertical distribution of veligers, pediveligers and post-larvae of the mussel Mytilus edulis L. was examined in Kandalakshsky Gulf (White Sea), Russia. Plankton samples showed that about 65 % of all planktonic larvae were collected from a depth of 1.5 to 3 m. Maximum numbers of veligers were found at 3 m, immediately above the thermocline. The vertical distribution of veligers was stable throughout the study, The vertical distribution of pediveligers, however, varied over time. Pediveligers were mostly observed at 3 m before settlement peaked while they migrated closer to the water surface (1.5 m) during the settlement period, Pediveliger concentrations were correlated positively with small phytoplanktonic cell (< 150 mum) and dissolved organic matter concentrations before settlement peaked, Both factors were correlated negatively with pediveliger concentrations during the settlement period. Newly settled post-larvae mainly colonized settlement panels situated at 1.5 m below the water surface (ca 70 % of total post-larvae abundance). These results support the hypothesis that planktonic larvae of M. edulis change their vertical distribution in relation to larval stages, which in turn, increases settlement success.