Temperature tolerance of Iceland scallop, Chlamys islandica (OF Muller) under controlled experimental conditions

The effects of temperature on the survival and behaviour of two size classes of Chlamys islandica was investigated in a laboratory study. The scallops were sampled in spring from three localities in Iceland, Breidafjordur (west), Hunafloi (north), and Hvalfjordur (southwest) and again in August from Breidafjordur and Hvalfjordur. Daily observations of mortality and behaviour were made over a 21-day period at sea temperatures ranging from 7 to 16degreesC in spring (April-May) and 11 to 14degreesC in August. During the spring experiment the tolerance of scallops, as expressed by mortality and behaviour, was distinctly reduced at sea temperatures above 12degreesC among scallops from Breidafjordur and Hunafloi and above 13degreesC among scallops from Hvalfjordur. During the second set of experiments, conducted in August, scallops were transported into the laboratory from a higher sea temperature than in the spring. As a result, mortality rates were much lower demonstrated by the fact that only scallops reared at sea temperature of 14degreesC died. This indicates that C. islandica may tolerate somewhat higher temperatures than have been observed in Icelandic waters in recent years. However, the gradual increase in temperature during the last 10 years has brought the mean temperature close to the species' tolerance limit.