Settlement of Mytilus galloprovincialis on collectors suspended at different depths in Bahía de Todos Santos B. C., Mexico

The blue mussel Mytilus galloprovincialis is cultured in Bahía de Todos Santos where it sustains a growing economic activity. This culture depends on seed collection from artificial collectors in the environment. It is known that the settlement season takes place from late autumn to early winter. However, there is no information on the settlement in different points of the culture area or at different depths. Neither is there knowledge on size composition of the settling population under these conditions. This information is useful for improving seed collection practices and for improving the understanding of the substrate colonization. For obtaining this information, pieces of about 105 cm2 of synthetic fibrous material were used as collectors and were placed at 2, 5, 7, 9, 10, 11, 13, 15 and 18 m depth in three points of the culture area during the settlement season. Additionally, an analysis of size composition of the settling population was carried out. Major settlement occurred in January in the three studied points. Settlement decreased according to the orientation of the sampling point with respect to the current from West to East, and according to depth. Higher values were found at 2 m depth and lower values were found at 18 m depth in all the three points. Settlement in February dropped nearly 43% with respect to January and it was relatively uniform in the 3 studied points. Size composition of the settling population shows that the greatest percentage (98%) settled directly as competent larvae and only 2% corresponded to drifting post-larvae. Around 40% of the seed was collected below 7 m depth; thus, mussel growers could place their collectors between all the studied depths for catching more seed.