Effects of oil pollution on the freezing tolerance and solute concentration of the blue mussel Mytilus edulis

Exposure of blue mussels (Mytilus edulis L.) to oil-polluted sea water for 7 d in the laboratory did not affect their body fluid concentrations of inorganic ions and free amino acids. Mussels exposed to-4°C for 12 h did not freeze, whereas freezing occurred invariably in mussels exposed to-7°C or lower temperatures for the same period. Following freezing at-10°C, oil polluted mussels resumed normal activity considerably more slowly than unpolluted ones, but oil-polluted as well as unpolluted mussels showed normal activity 3 h after thawing. Freezing at-15°C was invariably lethal to individuals of both groups. One possible explanation of the delayed recovery of oil-polluted mussels frozen at-10°C may be that oil components had become concentrated to toxic levels as the amount of solvent water diminished during freezing.