Ecological studies on the deep-water pelagic community of Korsfjorden, Western Norway population dynamics of<i>Meganyctiphanes norvegica</i>(Crustacea, Euphausiacea) in 1968 and 1969

Abstract

Abstract Horizontal samples taken on a monthly basis at six depths confirm that M. norvegica breeds in the spring in Korsfjorden. Individuals become mature at an age of one year and can live for just over two years. The population is subject to marked fluctuations, becoming very scarce in the spring and early summer, and an attempt has been made to eliminate this seasonal effect by calculating monthly values of an “environmental factor”. A single empirical expression has been obtained which describes recruitment and mortality of all the sampled generations, based on an adjusted time scale which takes account of seasonal variation in the rate of change. Constants obtained for each generation afford a measure of its relative abundance. The various generations showed evidence of compensatory growth, a relatively high rate in one season being followed by a lower rate and vice versa. Mean growth in carapace length is best described by two equations, again on an adjusted time scale. Younger animals are distributed at a lesser depth than older ones. The level and timing of the autumn increase in numbers strengthen the supposition that this increase is due to an influx from outside.