The Biology of the Marine Planktonic Copepods of Scoresby Sound, East Greenland

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Abstract
An account is given of the abundance and size-changes of the common marine copepods throughout the year. In Calanus finmarchicus some specimens hatched during the summer may attain maturity that same autumn below the 50-m level. Most of the remainder reach maturity in the following summer, and a certain number survive through yet another year. Although food conditions are responsible for the changes in size, large and small groups of the late stages often represent different year-groups. Calanus hyperboreus, breeding earlier than C. finmarchicus, exhibits unimodal size-groups in the late stages and probably comes to maturity in 1 year. In Pseudocalanus minutus most individuals pass through 1 generation a year, those hatching in summer reaching maturity that autumn or winter as a numerically large group of small size. Some moult to the mature state the following summer and appear as a minority of individuals of large size, and some of these apparently survive a 2nd winter. In Oithona similis most individuals pass through 1 generation a year, some through 2. Microcalanus pygmaeus passes through 1 generation at the surface, most of the young stages developing early in the year before the phytoplankton. It may have a 2nd generation below the 50_m level over the period of phytoplankton production. It shows a wide size variation. Metridia longa and Pareuchaeta pass through 1 generation in the year, breeding in the depths over summer. Species which develop through the summer appear able to pass through their life-cycle in about 20 weeks; those which develop in winter take longer. Microcalanus develops through several stages in winter: this can only mean that some form of predacious feeding goes on, although it does not have strongly raptorial mouthparts. Other apparently filter-feeding copepods may also obtain food in winter by predation. Nauplii and small stages of Oithona which may serve as food for larger copepods are present in considerable numbers throughout the year. There is a lag of about a week between time of attainment of maximum size of 1 cope-podite stage and beginning of the next more advanced stage. Development time from stage to stage is about a month; therefore the size attained by a copepod on moulting from one state to the next is due almost entirely to the state of nutrition at the time of the moult and but little to the size of the preceding stage. The winter size-increase of Calanus and Pseudocalanus, hitherto undescribed, occurs simultaneously in all the later stages. It is attributed to upward movement of large individuals formed in summer which had sunk to lower levels than the smaller individuals in the autumn and spring. This mid-winter increase in size indicates that some individuals survive for 2 years.

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