From macro-models to macroalgae: assessing the impacts of climate change on farmed and wild populations in the marine environment

Sammendrag

This thesis investigates potential impacts and sources of resilience for marine systems in the face of climate change. Throughout, a risk management framework is used to better identify risks posed to aquaculture species by climate change, analyze the potential of proposed interventions to reduce this risk, and assess the impact of ongoing mitigation measures within Norwegian kelp aquaculture. The first chapter looks at global aquaculture under a range of climate change scenarios to identify regions and species most exposed to climate dissimilarity, an alternative metric to assess climate change vulnerability. Here, it was revealed that under a conservative climate change scenario corresponding to Paris Agreement adherence existing aquaculture production is largely unimpacted. However, under increased emissions scenarios all major aquaculture producers experience significant climate dissimilarity – environmental conditions currently not found within the native range of key aquaculture species. While relocation of aquaculture within currently productive Exclusive Economic Zones (EEZs) can avoid projected climate dissimilarity, impacts on emerging aquaculture in enclosed seas are harder to avoid, posing challenges for proposed development in areas such as the Baltic Sea. The second chapter utilized Species Distribution Models (SDMs) to determine how much of a thermal tolerance increase is required to reduce or reverse projected reductions in the ranges of cold-adapted, economically important kelp in the North Atlantic. Though approaches to enhancing thermal tolerance in kelp are increasingly available, the thresholds guiding their development and application were lacking. This study demonstrates that a tolerance increase of 1-2C can halve losses across species and climate change scenarios. However, areas with highly productive kelp forests and kelp cultivation economies such as Maine require tolerance increases beyond 2C in most climate change scenarios, highlighting the need for approaches that match regional needs. While portions of the southern range extent in North America are not recoverable with modeled tolerance increases up to 5C, areas such as Scotland and Northern Norway are not projected to experience losses under any climate change scenario, even without an increase in tolerance. The findings of chapter two highlight the need for a two-pronged approach to conserve cold-adapted kelp forests: stringent reductions in greenhouse gas emission reductions in line with the SSP1-1.9 scenario, and strategies to boost kelp’s thermal tolerance by at least 1-2°C. This dual approach is crucial to maintain 90% of the current suitable habitat of S. latissima and L. digitata, and 70% for A esculenta and L. hyperborea. Existing techniques, such as thermal priming, can contribute to this target, but more aggressive interventions such as genetic modification and interspecific crossing may required to minimize losses under scenarios with increased warming. The third chapter compares genetic profiles obtained via whole genome sequencing of farmed and wild populations of Saccharina latissima from a 900 km stretch of the Norwegian coastline. By incorporating samples from a spectrum of cultivation approaches, comparisons within and between the groups provides a basis to assess the role of cultivation versus geographic distance in driving the genetic differentiation of these populations. When compared, cultivation approaches involving multiple years as vegetative gametophyte cultures produced genetic differences at the same magnitude as were observed between wild samples collected 800 km apart on opposite sides of significant oceanographic barriers. However, the absolute genetic distance between all samples remained relatively low, highlighting the high overall connectivity between populations in the study area. This first description of the concrete impact of cultivation method on genetics provides key information for farmers and policymakers seeking to facilitate strain enhancement without compromising the integrity of wild populations. These findings suggest that commercial cultivators may be able to source naturally advantageous parent material from further away if it is directly outplanted in the same growth year, though precautionary management is still warranted. Overall, this thesis examines the threat posed by climate change from global to local scales through techniques ranging from macro models covering all marine aquaculture species to molecular markers in specific macroalgae. Taken together, these results that while mitigation measures and climate-aware marine management can reduce the impact of climate change, they are no substitute for global policy to dramatically reduce emissions in line with the Paris Agreement.