Could offspring predation offset the successful reproduction of the arctic copepod Calanus hyperboreus under reduced sea-ice cover conditions?

• Published in: Progress in Oceanography
• Main Authors: Darnis, Gérald, Wold, Anette, Falk-Petersen, Stig, Graeve, Martin, Fortier, Louis
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2019
• Subjects: Amundsen Gulf; Arctic; Arctic copepod; Beaufort Sea; bowhead whale; Calanus hyperboreus; Phytoplankton; Sea ice; Copepods
• Online Access: https://epic.awi.de/id/eprint/48531/; https://epic.awi.de/id/eprint/48531/1/2018_Darnis-etal-Calanus-hyperboreus.pdf; https://doi.org/10.1016/j.pocean.2018.11.004; https://hdl.handle.net/10013/epic.20ba0952-70cd-496f-8ef0-8d20fc4e3554

Life cycle and reproduction of Calanus hyperboreus were studied during a year of record low ice cover in the southeastern Beaufort Sea. Stages CIV, adult females and CV dominated the overwintering population, suggesting a 2- to 3-year life cycle. Within two spring-summer months in the upper water column females filled their energy reserves before initiating their downward seasonal migration. From February to March, vigorous reproduction (20–65 eggs f−1 d−1) delivered numerous eggs (29 000 eggs m−2) at depth and nauplii N1-N3 (17 000 ind. m−2) in the water column. However, CI copepodite recruitment in May, coincident with the phytoplankton bloom, was modest in Amundsen Gulf compared to sites outside the gulf. Consequently, C. hyperboreus abundance and biomass stagnated throughout summer in Amundsen Gulf. As a mismatch between the first-feeding stages and food was unlikely under the favourable feeding conditions of April-May 2008, predation on the egg and larval stages in late winter presumably limited subsequent recruitment and population growth. Particularly abundant in Amundsen Gulf, the copepods Metridia longa and C. glacialis were likely important consumers of C. hyperboreus eggs and nauplii. With the ongoing climate-driven lengthening of the ice-free season, intensification of top-down control of C. hyperboreus recruitment by thriving populations of mesopelagic omnivores and carnivores like M. longa may counteract the potential benefits of increased primary production over the Arctic shelves margins for this key prey of pelagic fish, seabirds and the bowhead whale.