Ecological consequences of climatic forcing in the Arctic marine benthos

Abstract

Climate change is causing unprecedented changes in high-latitude environments, which have widespread implications for the underlying ecology and global climate and ocean systems. Of particular concern is the Arctic seafloor, an integral component of sympagic-pelagic-benthic food-webs, biogeochemical cycling and a variety of ecosystem services. Arctic climate change studies often overlook changes in the physiological, behavioural, and life-history traits of organisms, instead focusing on observable, macro-level responses such as range shifts and biomass turnovers. However, alterations of trait expression are crucial in determining an organism's capacity to adapt and influence the environment, preceding population and community-level responses. Substantial variability of trait expression is already observed across different spatiotemporal scales, between co-existing species and within conspecifics. As a result of these complexities, accurately assessing the impact of climate change on Arctic benthic biodiversity and ecosystem functioning is challenging. Here, I use laboratory-based mesocosm experiments, geochemical tracer analyses and simulative ecological extinction scenarios of Arctic benthic model systems to evaluate the consequences of organism responses to climate-driven environmental changes for benthic ecosystem functioning. Overall, my results demonstrate that organism responses are not generic, and can fundamentally alter their ability to persist and mediate aspects of ecosystem functioning. Specifically, I find that the capacity of species to endure climate-induced environmental change does not always equate to sustained contributions towards functional processes such as nutrient cycling and incurs inter- and intra-specific shifts in behaviour and physiological costs within metabolic pathways. Diverse responses to climate change are also reflected in the paleorecords, where intra-specific variability within long-lived cold-water corals influences their reliability in reconstructing deep-water temperature and seawater barium concentrations. Upscaling from organism responses to species turnover and community-level ecosystem functioning requires an appropriate acknowledgement of species interactions. By factoring in species co-dependencies during the “borealisation” of benthic assemblages, I demonstrate that co-extinctions can intensify the loss of community functioning, while concurrently observing a larger compensation effect from local and surrounding species pools. As such, I provide evidence that incorporating connections between taxa into predictions of biodiversity change enables more realistic assessments of systemic responses to climate-driven environmental change. Collectively, my findings highlight the influence of context on biodiversity responses and their repercussions on ecosystem functioning. In particular, I show that both individual organisms and entire assemblages from south of the Polar Front exhibit different responses to climatic forcing compared to north of the Polar Front and at its transition. In doing so, I draw attention to the importance of incorporating gradients of environmental variability into climate change assessments. I conclude that both environmental and biological variability shape the responses of Arctic benthic invertebrates to climatic forcing and the repercussions on ecosystem functioning. Rather than continuing to generalise responses at the macro-level, climate assessments should move towards incorporating the environmental context, interactions between organisms as well as intra- and inter-specific trait variability to accurately assess cascading effects on ecosystems. Integrating these components enhances our understanding of ecological responses to environmental change and improves predictions of future ecosystem dynamics. This knowledge is crucial for informing the most effective policy and management decisions aimed at mitigating stressor impacts.

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Identifiers

ORCID for Tom Williams: orcid.org/0000-0002-6616-955X

ORCID for Martin Solan: orcid.org/0000-0001-9924-5574

ORCID for Jasmin Godbold: orcid.org/0000-0001-5558-8188

ORCID for Phillip Fenberg: orcid.org/0000-0003-4474-176X

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