Abstract
Planktonic copepods of the genus Calanus play a central role in North Atlantic/Arctic marine food webs. Here, using molecular markers, we redrew the distributional ranges of Calanus species inhabiting the North Atlantic and Arctic Oceans and revealed much wider and more broadly overlapping distributions than previously described. The Arctic shelf species, C. glacialis, dominated the zooplankton assemblage of many Norwegian fjords, where only C. finmarchicus has been reported previously. In these fjords, high occurrences of the Arctic species C. hyperboreus were also found. Molecular markers revealed that the most common method of species identification, prosome length, cannot reliably discriminate the species in Norwegian fjords. Differences in degree of genetic differentiation among fjord populations of the two species suggested that C. glacialis is a more permanent resident of the fjords than C. finmarchicus. We found no evidence of hybridization between the species. Our results indicate a critical need for the wider use of molecular markers to reliably identify and discriminate these morphologically similar copepod species, which serve as important indicators of climate responses.
Highlights
Copepods of the genus Calanus are central in North Atlantic and Arctic pelagic food webs
Four species of the genus Calanus occur throughout the North Atlantic and Arctic Oceans: C. helgolandicus (Chel), C. hyperboreus (Chyp), C. finmarchicus (Cfin) and C. glacialis (Cgla); and there has been considerable effort to document and model their distributional changes [1,2]
Identification of Calanus species using molecular markers revealed that all four species have much wider distributional ranges than previously reported, as suggested by an earlier molecular study [6]
Summary
Copepods of the genus Calanus are central in North Atlantic and Arctic pelagic food webs. Four species of the genus Calanus occur throughout the North Atlantic and Arctic Oceans (figure 1): C. helgolandicus (Chel), C. hyperboreus (Chyp), C. finmarchicus (Cfin) and C. glacialis (Cgla); and there has been considerable effort to document and model their distributional changes [1,2]. We re-examine the distributional ranges of four cooccurring Calanus species in the North Atlantic and Arctic Oceans, using six molecular markers designed to ensure reliable species identification.
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