| Summary: | Calanus finmarchicus sensu lato belongs in the order Copepoda of the class Crustacea. It is probably the most widespread marine copepod, being found throughout the world in all but the tropical seas. Over much of its distribution it is the dominant member of the zooplankton and is an essential part of the food web on which many economically important fish depend. An understanding of its ecology will play a fundamental part in the scientific management of fisheries. The aim of the thesis is to attempt an understanding of certain aspects of this vast subject. The scope of the thesis has been broadened, paradoxically perhaps, by previous work which has produced various opinions on the systematic status of populations in different water masses. It has been necessary, therefore, to define the main populations in systematic terms and then to use these definitions in a number of ecological studies. The scientific history of Galanus finmarchicus s.l, began two hundred years ago with its discovery and description, as Monoculus finmarchicus, by Gunnerus. Today it has been suggested that it should be regarded as a complex of seven species, each characteristic of different water masses. Three of these, C, finmarchicus, sensu stricto, C. glacialis and G. helgolandicus are known from the North Atlantic and they form the subject of the present investigations. Morphological separation of these species is based mainly on the structure of the fifth (last) pair of limbs; in adult females and stage V copepodids the shape of the inner border of the coxopodite and the size of the teeth on this border are the main characters. In C. finmarchicus the teeth are small and the border approximately straight; C. glacialis, which is larger than the other two, also has small teeth on a concave border; and C. helgolandicus has larger teeth on a strongly concave border. Adult males are distinguished mainly by different proportional lengths of the rami of this pair of limbs. The material for the investigations has come for the most part from ...
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