Comparative settlement depths of Mytilus edulis C. Linnaeus, 1758 and M-trossulus Gould, 1850: I. A mesocosm study

摘要

Production on many commercial mussel farms in Eastern Canada is hampered by the presence of Mytilus trossulus. a comparatively thin-shelled but close relative of M. edulis, the principal species collected and grown. Exploitation of a species-based difference in depth preference could potentially increase the collection of M. edulis at mixed species sites. As a first step in the investigation, larval cultures of each species were reared to settlement in replicated mesocosms in a study conducted at Dalhousie University's Aquatron facility in Halifax, Nova Scotia. Depth preference for settlement was examined with and without a thermocline. Both M. edulis and M. trossulus had the largest percentage of larvae settling at the surface. Settlement occurred below the thermocline at 6 m in both species, although in significantly lower proportions. In mixed water, a significant species-depth interaction was detected. This was driven by a significantly large number of M. edulis spat settling at 8 m, a pattern not found in M. trossulus.