Data from: Genetics redraws pelagic biogeography of Calanus

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 hybridisation 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.