Temperature tolerance of Iceland scallop, Chlamys islandica (O.F. Müller) 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, Breidafjördur (west), Húnaflói (north), and Hvalfjördur (southwest) and again in August from Breidafjördur and Hvalfjördur. Daily observations of mortality and behaviour were made over a 21-day period at sea temperatures ranging from 7 to 16°C in spring (April-May) and 11 to 14°C in August. During the spring experiment the tolerance of scallops, as expressed by mortality and behaviour, was distinctly reduced at sea temperatures above 12°C among scallops from Breidafjördur and Húnafló i and above 13°C among scallops from Hvalfjördur. 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 14°C 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.