Secondary production at the Barents Sea polar front in summer: contribution of different size classes of mesozooplankton

The Barents Sea polar front is characterized by high primary production following the retreat of the ice edge during spring. However, secondary production estimates of mesozooplankton across the front are scarce, despite being essential for understanding energy flow through the food web. We investigated mesozooplankton community composition and production across the Barents Sea polar front (75 degrees-78 degrees N) in June, covering both Atlantic and Arctic water masses with high spatial and taxonomic resolution. We highlight the contribution of small and large groups of mesozooplankton and estimate secondary production by comparing and evaluating 4 commonly used growth rate models. The zooplankton community composition and size distribution changed across the polar front. In the Atlantic region, Rotifera, Chaetognatha and Appendicularia were common, while copepods and their nauplii contributed most across the polar front and in Arctic water masses. Mesozooplankton secondary production took place mainly in the surface and was highest south of the front, declining towards Arctic waters. Considering production by copepods alone, highest values were found in the northern sector of the polar front and in the Arctic region. Young developmental stages (CI-CIV) of Calanus spp. and small-sized taxa contributed most to copepod production in Atlantic waters, while calanoid copepod nauplii contributed considerably to copepod production in Arctic waters. We emphasize that the production estimates were strongly influenced by the growth rate model and conclude that copepod secondary production in a summer situation with non-limiting food concentration was best described using a model that solely considers water temperature and copepod body weight.