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.

哲水蚤属（Calanus）浮游桡足类在北大西洋与北极海洋食物网中占据核心地位。本研究借助分子标记，重新绘制了栖息于北大西洋及北冰洋的哲水蚤属物种的分布范围，并揭示其分布范围较此前报道的更为广阔，重叠分布区域也更为广泛。北极陆架物种冰川哲水蚤（C. glacialis）在诸多挪威峡湾的浮游动物群落中占据优势地位，而此前仅报道过芬氏哲水蚤（C. finmarchicus）在此栖息；同时在这些峡湾中，还发现了北极物种厚壳哲水蚤（C. hyperboreus）的高出现率。分子标记结果显示，最常用的物种鉴定方法——前体长度法，无法在挪威峡湾中可靠区分这两类物种。对这两个物种的峡湾种群间遗传分化程度的差异分析表明，冰川哲水蚤相比芬氏哲水蚤，是峡湾中更为持久的定居类群。本研究未发现这两个物种间存在种间杂交的证据。本研究结果表明，亟需更广泛地应用分子标记技术，以可靠鉴定和区分这些形态相似的桡足类物种——这类物种是气候响应的重要指示类群。