Multiple interacting stressors in Arctic Ocean ecosystems
By Rosalie Wright
Oceans provide many critical ecosystem services but face a complex array of interacting stressors, the cumulative impacts of which are not yet well understood. This is particularly prevalent in the Arctic Ocean, which experiences acute anthropogenic impacts (e.g., shipping, resource extraction) in addition to climate-related stressors.
Recently published in Nature Communications, research led by Arrigo et al. (2020) found that neglecting stressor interactions led to vastly underestimated risk of animal population crashes, highlighting the necessity of accounting for stressor interactions in comprehensive environmental risk assessment and management planning.
But how can we better understand complex stressor interactions? The combined pressures and drivers of change in marine systems cannot be easily studied in controlled experimental settings. Ecological modelling and analytical frameworks instead offer particularly useful tools for quantitative assessment of multiple stressors and predicting subsequent shifts in community dynamics. However, ecological modelling has traditionally considered only one or two impacts on a species or ecosystem, failing to address non-additive interactions such as synergistic (amplified) or antagonistic (dampened) effects.
Image source: Arrigo et al. 2020
Using a novel framework for modelling stressor interactions – the Ocean System Interactions, Risks, Instabilities, and Synergies (OSIRIS) model – Arrigo et al. demonstrated that chronic climate-related stressors (e.g., sea ice loss, warming seas, acidification), in the Chukchi Sea ecosystem were more harmful to animal populations than acute threats such as shipping and subsistence harvesting. The model included a range of trophic levels, from phytoplankton and Pacific salmon to polar bears and gray whales, and found that organisms varied greatly in sensitivity to multiple interacting stressors.
“We focus on the Arctic Ocean because it is changing rapidly as a result of warming, causing ecological upheaval and opening a “new ocean” for commercial and industrial development.”. The Chukchi Sea is also “one of the most productive ecosystems in the world and is characterized by a relatively simple food web… an ideal system for understanding the impacts of non-linear interactions among different environmental stressors on key marine species.”
The Nature Communications article clarifies three key takeaways from the modelling results: “First, synergistic interactions amplify adverse stressor effects on ocean ecosystems. Second, the impact of synergy is predicted to increase with the magnitude of stressors, which are anticipated to grow with expanded human activities. Third, synergies will make population and ecosystem responses more unpredictable.” In future, the team suggest that:
“Research should aim to identify possible levers for mitigating impacts, by, for example, identifying the stressors that more frequently and significantly interact synergistically with others. As such, research that increases our understanding and capacity to anticipate tipping points should be prioritized.”
With continually accelerating climate change, ecological models incorporating multiple interacting stressors will help to avoid underestimating the risks faced by marine environments and clarify the limitations of single-stressor management approaches. Quantifying and mapping ecological responses to multiple stressors will also support ecosystem-based management actions, that may help mitigate large-scale consequences to oceans and the services they provide.
Access the paper here: https://www.nature.com/articles/s41467-020-19899-z