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On the edge: The influence of multiple stressors on thermal tolerance in poleward edge populations in a climate change era

Periodic Reporting for period 1 - EdgeStress (On the edge: The influence of multiple stressors on thermal tolerance inpoleward edge populations in a climate change era)

Reporting period: 2020-02-01 to 2022-01-31

Global climate change has a profound effect on species and ecosystems across the globe. Temperatures at the equator are becoming too hot for many species to survive, and in response species are re-distributing to avoid deadly heat. They do so in a mainly poleward direction, and they are moving fast - more than 50-70 km per decade on average. The Arctic is warming 3 times faster than the global average, and non-Arctic species have started to expand into the Arctic seeking a ‘thermal refuge’ away from the heat. However, recent measurements indicate that temperatures in some Arctic regions already exceeds the temperature limit of many species, thus the Arctic may already too warm to provide shelter from climate change. Moreover, climate change is not only affecting species by warming their environment. In the Arctic, climate change is also causing ocean acidification (a decrease in the pH level of the water), and an unpreceded melting of the Greenland Ice Sheet, which decrease ocean salinity though a process called ‘freshening’. The project EdgeStress improves knowledge and perspectives on the effects of multiple climate change stressors on species and ecosystems at high latitudes.

Specifically, the overall objectives of the project are:

O1. Investigate if high summer temperatures lead to lethal heat stress in populations at their poleward limits.
O2. Investigate if the combination of several interacting stressors in a natural environment decreases the thermal tolerance of habitat-forming species, hereby changing ecosystem structure.
O3. Investigate if freshening and increased warming allow the expanding blue mussel Mytilus edulis to outcompete a native sister species in the Arctic
This first period of the project has focused on Objective 1 and Objective 2.
To understand the effects of climate change on ecosystem structure and functioning, a requirement is to have a baseline description of the ecosystem. The intertidal system at high latitudes is poorly described, and global patterns in biodiversity isn’t well understood. I started analysing and describing intertidal ecosystem structure in Greenland and globally, and these results have been published. For Objective 1 have I placed biomimetic temperature sensors for measuring body temperatures of key species, and some mussels had their heart rate measured in the field. I am currently building heat and cold budget models for blue mussels based on these data in combination with environmental data.

Blue mussels have also been collected at sites with contracting salinity and temperature conditions, and some mussels were brought to the laboratory where I have conducted thermal tolerance experiments investigating if temperatures lead to lethal heat stress at high latitudes. The results from these studies so far shown a remarkable resilience in blue mussels to global warming. Physiological measurements have been done on all biological levels from genes, protein expression, to whole-animal responses, and the first results has been published. Furthermore, have I been exploring the effects of parasites on thermal tolerance. The preliminary results clearly show that parasite infections interfere with thermal tolerance of the host organisms.
I have investigated the interaction of ocean acidification and thermal stress on several blue mussel species. We have studied the processes behind the effects of acidification on thermal tolerance using NMR analysis, amino acid composition and quantification analyses, and membrane fatty acid structure.

For Objective 2, I have fabricated settlement plates, which was developed in the research group. The panel has been deployed alongside salinity/temperature loggers to investigate the effects of warming using a field-based experiment. The panel are placed in areas of different salinity, hereby allowing for a comparison of salinity-temperature effects on community structure and species interactions.

I have been involved in several new projects. In these now collaborations I have, among other, conducted thermal tolerance experiments on native and invasive intertidal species to understand the effects of heat waves and cold waves on biodiversity and species distribution.
The data and results have already progressed the current state of the art. Little is known about how species cope with the climate change at higher latitudes, but I have shown that blue mussels at their northern edge are resilient to climate warming. For example, we found no evidence for cellular stress response in animals collected on a warm summer day in the Arctic, and for the first time identified a massive expansion of the HSPA12 heat shock protein in the blue mussel Mytilus edulis. This novel discovery indicates an unknown evolutionary adaptation to the intertidal life. Thus, blue mussels appear to have considerable capacity to withstand the current rates of Arctic warming, but I have also produced data showing that increased freshwater runoff from the Greenland Ice Sheet in response to warming render key intertidal species more sensitive to heat stress. From another of my studies, it seems that parasites increase thermal tolerance in some species, which was until now unknown, so the effects of multiple stressors work in different directions and their internal interactions are a fruitful topic for future research.

I have described how intertidal communities are controlled by local- rather than large-scale environmental drivers, and the Greenlands intertidal ecosystems seems resilient to climate change. This indicates that no major changes in community structure is expected in a near future. These results on the resilience of species and ecosystems at high latitude are novel, and the papers produced so far has moved beyond the current state of the art. Therefore they are receiving significant attention and is already being widely cited.

The results obtained in EdgeStress are important for scientists and societies as improved knowledge and perspectives on the effects of multiple climate stressors on individuals to ecosystems is crucial for understanding the effects on species survival, biodiversity changes and ecosystem stability. New information on multiple climate stressors on coastal systems is important worldwide. Coastal systems provide nursery grounds for commercially important fish and shellfish species, and ecosystem services such as, carbon sequestration and shoreline protection with an estimated value in the trillons of euro. The results from this project will therefore have implications for global and local communities and economies as it will be used to inform stakeholders, organisations, researchers, and the public about the future effects of climate change on one of the most sensitive ecosystems on earth.

Until the end of the project, I will continue to submit manuscript for peer-review in International leading journals. I will conduct more public outreach though participation in science festivals, and I plan write a popularised article.
Intertidal blue mussels at high latitudes