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KLIMAFORSK-Stort program klima

Plankton size and planktivore competition along the Norwegian coast and fjords: ecological implications of warmer and darker waters

Alternative title: Planktonstørrelse og beitegrunnlag for pelagisk fisk under oppvarming og formørking av økosystem langs Norskekysten

Awarded: NOK 8.0 mill.

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Project Period:

2023 - 2027

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Coastal waters are some of the most productive of marine ecosystems. In a changing climate, coastal waters are getting warmer and darker, and the ecological implications are unknown. In this project we will study how the foraging opportunities for pelagic fish (herring, sprat, mackerel etc.) may change as a result of these two climate change associated stressors. Pelagic fish are visual foragers, and the size and visibility of their prey (zooplankton) may be more important than prey abundance for fish foraging efficiency and production (Aarflot et al. 2020 MEPS). Both warming and coastal water darkening are expected to alter the size structure within plankton communities that have rapid life cycles and respond fast to changes in the environment. In this project we will expose historical zooplankton samples to new technology for revealing community size structures, and incorporate plankton size in an existing ecosystem model for Norwegian coastal waters. With this we aim to enhance our understanding of how temperature and light affects the size structure within planktonic communities along the Norwegian coast – both historically and in the future. If fish become less efficient predators, jellyfish may gain a competitive advantage as they do not rely on vision or prey size to localize their food. We will therefore also assess the competitive relationship between fish and jellyfish in selected Norwegian fjords, and the potential for regime shifts towards more jellies and less fish in the future.

Coastal waters are some of the most productive marine ecosystems. Ocean warming and increased light attenuation (reduced penetration of light into the water) are two climate change associated stressors impacting coastal waters, and the ecological implications are unknown. Both stressors may affect the size structure and dynamics within planktonic communities, which is important for fish foraging efficiency and energy transfer from primary production to higher trophic levels. Also, the optical foraging environment for fish may be impaired, potentially leading to ecosystem regime shifts. In PELAGIC, we will utilize stored zooplankton samples collected over a 30-year period and expose them to modern technology, establishing a novel dataset on the size structure of zooplankton in coastal waters. The data will be used to advance our understanding of how the quality of prey for pelagic fish (e.g., herring, sprat, mackerel) varies over spatial and environmental gradients and is affected under climate change. Furthermore, we will collect new light observations from Norwegian fjords and perform a theoretical assessment of the potential for increased dominance of jellyfish (at the expense of fish) as these waters gets darker. Ecosystem models are vital tools for assessing potential future states of marine ecosystems under climate change, but existing large-scale global and regional models do not resolve plankton communities in realistic dimension. With PELAGIC, we will develop an ecosystem model with more realistic plankton size structure and dynamics, and an improved light environment necessary for modelling plankton dynamics in coastal waters. Using this tool, we will assess how future plankton communities will be affected by ocean warming and coastal water darkening and potential consequences for the energy transfer to higher trophic levels in the ecosystem.

Funding scheme:

KLIMAFORSK-Stort program klima