Pushing the limit: Resilience of an Arctic copepod to environmental fluctuations

Abstract

Life history strategies such as multiyear life cycles, resting stages, and capital breeding allow species to inhabit regions with extreme and fluctuating environmental conditions. One example is the zooplankton species Calanus hyperboreus, whose life history is considered an adaptation to the short and unpredictable growth season in the central Arctic Ocean. This copepod is commonly described as a true Arctic endemic; however, by statistically analyzing compiled observational data, we show that abundances are relatively low and later stages and adults dominate in the central Arctic Ocean basins, indicating expatriation. Combining data analyses with individual-based modeling and energy requirement estimation, we further demonstrate that while C. hyperboreus can reach higher abundances in areas with greater food availability outside the central Arctic basins, the species' resilience to environmental fluctuations enables the life cycle to be completed in the central Arctic basins. Specifically, the energy level required to reach the first overwintering stage-a prerequisite for successful local production-is likely met in some-but not all-years. This fine balance between success and failure indicates that C. hyperboreus functions as a peripheral population in the central Arctic basins and its abundance will likely increase in areas with improved growth conditions in response to climate change. By illustrating a key Arctic species' resilience to extreme and fluctuating environmental conditions, the results of this study have implications for projections of future biogeography and food web dynamics in the Arctic Ocean, a region experiencing rapid warming and sea ice loss.

Zooplankton Communities Associated With New and Regenerated Primary Production in the Atlantic Inflow North of Svalbard

“…In addition, because the developmental time and survival of C. glacialis nauplii are sensitive to food quality, the chances to survive are higher when feeding on algae with high proportions of PUFAs (Daase et al, 2011). Due to efficient lipid synthesis and storage, both species can overwinter relatively young; C. glacialis mainly as CIII-CIV (Madsen et al, 2001;Søreide et al, 2010) and C. hyperboreus already as CIII (Kvile et al, 2018). The early egg laying, and the accessibility to high-quality and lipid-rich phytoplankton such as diatoms for the developing nauplii and young copepodids, allows these species to reach the overwintering stage within the first year.…”

“…Most obvious is perhaps the direct effect on the large herbivorous copepods, with life cycles tailored to utilize the short and intense spring bloom for reproduction and lipid synthesis (Falk-Petersen et al, 2009). For example, the large Arctic Calanus hyperboreus reproduce in winter, prior to the productive season (Falk-Petersen et al, 2009;Kvile et al, 2018), C. glacialis reproduce prior to and during the ice algae bloom (Varpe et al, 2009;Søreide et al, 2010) and C. finmarchicus has its main reproductive period during the open water spring bloom (Hirche, 1996;Pedersen et al, 2001). When the large Calanus species have built sufficient lipid storages, they enter diapause at depth to survive the long and less productive winter season.…”

Pan-Arctic Depth Distribution of Diapausing Calanus Copepods

“…This study is based on a recent compilation of published observational data spanning the Arctic Ocean and surrounding seas from the 1930s to present (Kvile et al, 2018). The dataset contains information on abundances of Calanus glacialis Jaschnov, 1955 and Calanus hyperboreus Krøyer, 1838 copepodid and adult stages per location, time, and depth interval.…”

“…We compiled observational data on C. glacialis and C. hyperboreus as described in Kvile et al (2018). In short, we compiled stage-specific abundance data on copepodid stages (C1-C5) and adults (C6 female or male; hereafter, C6f and C6m) from published sources (see Supplementary Table 1, available online).…”

“…However, this appears to contradict the positive association between bottom depth and SD-presumably reflecting that increased availability of suitable diapause habitat increases the breadth of the diapausing population. Alternatively, these results may reflect that, because of lower concentration and shorter duration of food supply, Calanus copepods are resource limited in the central Arctic Ocean and periodically unable to store sufficient lipid reserves for diapause (Ji et al, 2012;Kvile et al, 2018). Recent studies suggest that a combination of external cues, internal clock mechanisms, and lipid content triggers descent to diapause and that animals without sufficient lipid reserves will remain active in the upper waters (Häfker et al, 2018;Schmid et al, 2018).…”