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

Abstract

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.

Seasonal and interannual variability of the Queen Maud Gulf ecosystem derived from sediment trap measurements

“…With a composition dominated by M. longa , Microcalanus spp., Pseudocalanus spp., O. similis , T. borealis , and C. glacialis , the sediment trap assemblage was similar to the zooplankton community of Resolute Passage (Michel et al 2006). While the large oceanic copepod C. hyperboreus dominates the mesozooplankton biomass on the deep margins of the Arctic shelf seas and has frequently been observed in Barrow Strait (Michel et al 2006; Darnis et al 2019), only low numbers of C. hyperboreus stage C3 and older were collected in the sediment trap in the Gulf (Fig. 5e).…”

“…5e). As the life‐history strategy of C. hyperboreus involves a long overwintering season in diapause at depths of several hundred to thousands of meters (Ashjian et al 2003; Darnis et al 2019), it is unlikely that successful reproduction occurs in the rather shallow Gulf, explaining the absence of younger copepodite stages. Furthermore, vertical distribution of this species mostly at depth for a major part of the year would prevent its transport over the Gulf shoaling.…”

Sea-ice decline makes zooplankton stay deeper for longer

“…An earlier descent of omnivorous copepods such as Metridia spp. can lead to increased predation on C. hyperboreus nauplius larvae before they have outgrown the prey size range of Metridia spp, compromising the recruitment of C. hyperboreus 46 (Fig. 5).…”

Combining Traditional Taxonomy and Metabarcoding: Assemblage Structure of Nematodes in the Shelf Sediments of the Eastern Antarctic Peninsula

“…Nauplii are early larval stages of mainly copepods, and their assemblage can be a proxy for environmental changes. They are highly sensitive to environmental stressors, and indicate the recruitment of copepods, hence their reproductive success (Bunker and Hirst, 2004;Gonçalves et al, 2010;Darnis et al, 2019). The variability of larval stages is typically linked to the availability and quantity of food, thus potentially representing a proxy of surface primary productivity in DB.…”