Life cycles and seasonal vertical distributions of copepods in the Iceland Sea

Abstract

The sub-Arctic Iceland Sea is an important feeding area for the Icelandic capelin stock with copepods as a major food item. Information on the life history of copepods in the area is limited, and therefore the major aim of the present paper is to describe the population development and ontogenetic vertical migrations of dominant copepods in the area. Depth stratified samples were collected on six cruises covering all seasons of the year from 2006 to 2008. Calanus hyperboreus dominated the biomass (~ 45% of copepods), with C. finmarchicus ranking second (~ 28%) and Metridia longa third (~ 17%). The copepods differed in their life history strategies. C. hyperboreus is unique in that it has the deepest winter distribution (~ 800–1000 m), reproduces at depth in February–March in the absence of phytoplankton food, and spends relatively short time in the surface layers during summer. C. finmarchicus also hibernates at depth, however much shallower (~ 200-600 m), and the reproduction at the surface in May–June is timed to the productive period of phytoplankton. A 2- to 3-year life cycle is proposed for C. hyperboreus and a 1 year for C. finmarchicus. Pseudocalanus spp. appear to have a similar life history as C. finmarchicus, while occupying intermediate depths (~ 400–1000 m) during the overwintering period. The life history of the omnivorous species M. longa appears relatively decoupled from the phytoplankton spring bloom. The same applies to the omnivorous species Oithona spp. and Oncaea spp. The information presented adds to the comparative description and understanding of copepods in sub-Arctic areas in general.