Comparative life histories in the genera Calanus and Neocalanus in high latitudes of the northern hemisphere

Abstract

At least nine species of Calanidae occupy the area of interest, four in the Atlantic and five in the Pacific. All store wax esters and probably can undergo diapause. Latitudinally overlapping or onshore-offshore associations of two or more species occur in both oceans. Interzonals, with reduced mouth parts in the adult female, arc endemic to the Pacific subarctic gyre where their life cycles are completed in one year. Presumably its nearly closed circulation and environmental stability have favored the evolution of endemic species well adapted to those conditions. Lack of ice-and/or salinity-induced stability also limits blooms there. The sub-arctic Atlantic contains several smaller oceanographic features, open to both arctic and Atlantic influences and populated by species of different origins, arctic species can behave as interzonals but may also require two or more years to complete their life cycles. Females may need to feed one year to reproduce the next and therefore they retain functional mouthparts. In some places in the North Atlantic, blooms may start in the sub-ice zone and seed the remaining euphotic zone. There the earliest stages of some the Calanus species can develop close to the ice, using primarily ice algae as food, while the remaining stages are adapted to utilize brief periods of intense primary production in the water column. Salinity-induced stability and shallow water favor blooms in the boundary waters of both oceans, which may be of greater importance in the Atlantic because of the proportionally greater area of continental shelf there. In both oceans the smaller species of Calanidae can produce up to three generations per year.