MEPS 228:143-152 (2002)  -  doi:10.3354/meps228143

ABSTRACT: The effect of salinity (5 to 25 ppt) on Mytilus edulis and M. trossulus that co-exist in Atlantic Canada was examined in 2 laboratory experiments. The first experiment tested the effect of salinity on survival and duration of development from fertilization to settlement in the 2 species. Hyposalinity reduced survivorship and percent metamorphosis, and lengthened duration of development. At 5 and 10 ppt, all early stages of both species died. At 25 ppt, >90% of individuals of both species survived through the oocyte to swimming embryo and swimming embryo to D-veliger stages, but only ca. 40% survived through the D-veliger to eyed-veliger stage, and 30 to 42% of eyed-veligers successfully metamorphosed. At 15 ppt, the 2 species significantly differed in survival rate, duration of development, and metamorphosis. M. edulis did not develop through any of the 3 stages from oocyte to eyed-veliger. No M. edulis eyed-veligers metamorphosed. In contrast, in M. trossulus, 26% of oocytes and 15% of swimming embryos developed into swimming embryos and D-veligers, respectively, and 13% of eyed-veligers metamorphosed into plantigrades. At 20 ppt, some M. edulis developed through each of the 4 stages, but the development time was longer and there was a lower percentage than for the corresponding stage of M. trossulus. The second experiment examined the effect of salinity on survival of juveniles and adults. The 2 species responded to hyposaline stress similarly. Survival ranged from 0 at 5 ppt to 100% at 20 to 25 ppt. At 10 ppt, reproductive status affected mortality, with <5% mortality in juveniles and post-spawning individuals, but 60 to 67% mortality in reproductive mussels. A similar situation occurred at 15 ppt except there was lower mortality for reproductive individuals. Thus, we found that only in the early ontogenetic stages was M. edulis less tolerant to low salinity stress than M. trossulus. Such difference suggests that selective mortality against M. edulis in early ontogenetic stages rather than post-settlement stage may be responsible for the persistence of a few pure M. trossulus populations along the Gaspé Peninsula. We also found that the ability to tolerate hyposalinity was weakened during the reproductive period, which indicates that salinity may also act as a selective factor in determining the abundance and size structure of wild mussel populations.

KEY WORDS: Mussel · Mytilus · Salinity · Ontogeny · Life cycle