Within the EU, there is a strong incentive towards developing sustainable, low-trophic aquaculture. At the same time, climate change leads to changes in temperature, freshwater inputs and stratification in the marine environment , affecting nutrient and primary production patterns. This can subsequently affect the system’s carrying capacity for low-trophic, extractive aquaculture. As part of the FutureMARES EU Horizon H2020 project, we investigated the potential for large-scale sugar kelp and mussel aquaculture in the Dutch North Sea , and how it might be influenced by climate change.
We used a 3D coupled hydrodynamics, water quality and ecology model of the North Sea. Within the model, we also computed s ugar kelp and mussel dynamics, together with their respective feedbacks on the environment. We simulated hypothetical large-scale cultivation scenarios for both species, separately and combined. In the Netherlands, future offshore aquaculture will be co-located in wind farms. In our simulations, we therefore placed the aquaculture farms within planned offshore wind farms , based on their suitability for cultivation of the simulated species . These upscaling scenarios were run for a historical state, and for 2050 and 2100 conditions according to a global sustainability scenario and a more pessimistic scenario with respect to climate change.
Our results show that sugar kelp cultivation yields close to a 1 kgDW/m2 target can be achieved in every farm of the historical state. For the most sustainable scenario, y ields achieved in 2100 are 2-10% higher than in the historical state , due to higher winter nutrients along the Dutch coast. In the least sustainable scenario, temperatures simulated in 2100 are significantly higher and offshore nutrients in the Dutch EEZ are lower. Consequently , simulated sugar kelp yields are 2-16% lower compared to the historical state. Results from mussel cultivation scenarios show that final cultivation yields vary much more from one farm to another and are more sensitive to the cultivation density, than for sugar kelp . Highest yields are achieved in the most near-shore farms with in the Rhine region of freshwater influence, receiving high nutrient loads and exerting higher primary production . When large-scale mussel cultivation is combined with large-scale sugar kelp cultivation, the production yields for both species are not significantly altered.
Additional runs were performed including flat oyster beds in areas potentially suitable for restoration , in addition to large-scale low-trophic aquaculture . Results show that the presence of oyster beds might affect mussel cultivation yields negatively, but they have very little effects on sugar kelp yields. Using the same model , we also investigated the effects that cultivation scenarios have on the environment (e.g. nutrients and phytoplankton). In all cases, cultivation at such large scales lead to significant decreases in phytoplankton biomass, which may impact the marine food chain.