Ecological studies on the deep-water pelagic community of Korsfjorden, Western Norway the Species ofPasiphaeaandSergestes(Crustacea Decapoda) recorded in 1968 and 1969

Abstract

P. multidentata, P. sivado, P. tarda, and S. arcticus were obtained in a series of Isaacs-Kidd samples taken at monthly intervals at depths between 100 and 440 m during the day and between the surface and 400 m during the night. P. multidentata and P. tarda become morphologically distinct at a carapace length of about 12 mm. P. multidentata, the commonest species, breeds throughout most of the year with indications of greater activity in early or mid summer and in late autumn or winter. Maturity is reached at a carapace length of about 18 mm and age of one and a half years. Few specimens live for more than two years. At least two broods are produced and fecundity shows a loose relationship with carapace length. Most specimens occur at depths of 300–400 m during the day-time and there is clear indication, particularly among the larger specimens, of an upward migration at night. It is likely that the Korsfjord population of P. sivado must be recruited from outside as only one generation, which was probably spawned in early autumn 1967, was recorded; the last specimens were taken in September 1969. The growth rate is a little slower than that of P. multidentata, and maturity is attained at an age of about 15 months. P. tarda is rarely found in pelagic hauls but probably maintains a population near the bed of the fjord (690 m). There is evidence of an autumn generation. S. arcticus breeds in the spring in Korsfjorden. Individuals become mature when a year old and can probably live for upwards of two years. Females show a higher growth rate than the males.