On the acclimatization ofCalanus finmarchicus(Crustacea, Copepoda) to different temperature conditions in the North Atlantic

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Abstract
Data on the distribution of the developmental stages of Calanus finmarchicus (Gunnerus) obtained during the Norwestlant Surveys have been used to study the timing and rate of development of the spring generation in the north-west Atlantic. It was found that breeding was starting uniformly over the whole area in April. It is suggested that a widespread environmental factor, such as the increasing light in spring, is responsible for maturation of the population. Later a geographical pattern began to emerge so that by July the generation was most advanced in the southern off-shore waters and on the Icelandic shelf, and least advanced in the far north, on the shelf round Greenland and off the coast of Labrador. There was found to be a loose relationship between temperature and the speed of development which became more precise when the data were divided up according to geographical regions; the individual relationships showed displacement relative to each other. It is suggested that this indicates the existence of populations acclimatized to different temperature conditions, such that those populations in the cold areas, as well as those in warmer water, can complete a generation in the year. These conclusions are compared with those of Fox (1939) concerning the acclimatization of poikilothermal animals.