Temporal patterns in multiple stressors shape the vulnerability of overwintering Arctic zooplankton

Our study investigates the winter survival of the Arctic copepod C. glacialis under multiple stressors, exploring stressor temporal dynamics and exposure duration. We conducted experiments with pulse (intermittent) and press (continuous) exposure temporal scenarios, involving microplastics, pyrene, and warming in a fully factorial design. We observed significant effects on copepod survival, with pronounced impacts during later stressor phases. Two-way interactions between microplastics and pyrene, as well as pyrene and warming, showed significant effects, further intensified with the presence of a third stressor. Continuous stressor exposure for 9 days (press temporal scenario) led to greater reductions in copepod survival compared to the pulse scenario, characterised by two 3-day stressor exposure phases. Notably, the inclusion of recovery phases, free from stressor exposure, positively influenced copepod survival, highlighting the importance of temporal dynamics. Our findings underscore the intricate interactions among multiple stressors and their temporal patterns in shaping overwintering Arctic copepod responses. This study has crucial implications for managing Arctic aquatic ecosystems in the context of ongoing climate change, highlighting the need to predict and mitigate combined stressor effects in these environments.

Methods

In January 2023, copepods were sampled near Billefjorden in the Arctic using a Zooplankton Net from the RV Helmer Hanssen. Collected copepods, specifically in the main diapausing and CIV, CV stages of Calanus glacialis, were transported to a controlled-temperature room at the University Centre in Svalbard (UNIS) within a day. After sorting, selected specimens were sent to the University of Oslo for an experiment in February 2023.

The experiment, conducted at the Department of Biosciences, involved exposing C. glacialis to three stressors (warming, microplastics, and pyrene) in a fully crossed design. Three temporal regimes were examined: pulse (stressors applied twice for 3 days each with recovery phases), press (continuous exposure for 9 days with a single 5-day recovery phase), and a control group with no stressor exposure. The pulse treatment spanned 14 days, and the press treatment lasted for 14 days as well.