Impacts of climate change on water quality, benthic mussels, and suspended mussel culture in a shallow, eutrophic estuary

Marie Maar; Janus Larsen; Momme Butenschön; Trond Kristiansen; Hans Thodsen; Daniel Taylor; Vibe Schourup-Kristensen

doi:10.1016/j.heliyon.2024.e25218

Impacts of climate change on water quality, benthic mussels, and suspended mussel culture in a shallow, eutrophic estuary

Heliyon. 2024 Jan 28;10(3):e25218. doi: 10.1016/j.heliyon.2024.e25218. eCollection 2024 Feb 15.

Authors

Marie Maar¹, Janus Larsen¹, Momme Butenschön², Trond Kristiansen^{3

4}, Hans Thodsen⁵, Daniel Taylor⁶, Vibe Schourup-Kristensen¹

Affiliations

¹ Department of Ecoscience, Aarhus University, Frederiksborgvej 399, PO Box 358, 4000 Roskilde, Denmark.
² CMCC Foundation-Euro-Mediterranean Center on Climate Change, Bologna, Italy.
³ Farallon Institute, 101 H St., Petaluma, CA 9495, USA.
⁴ Actea Inc, San Francisco, CA, USA.
⁵ Department of Ecoscience, Aarhus University, CF Møllers Allé 3, 8000 Aarhus C, Denmark.
⁶ Section for Coastal Ecology, National Institute of Aquatic Resources, DTU Aqua, 7900 Nykøbing-Mors, Denmark.

Abstract

Climate change is a global problem that causes severe local changes to marine biota, ecosystem functioning, and ecosystem services. The Limfjorden is a shallow, eutrophic estuary influenced by episodic summer hypoxia with an important mussel fishery and suspended mussel culture industry. Three future climate change scenarios ranging from low greenhouse gas emissions (SSP1-2.6), to intermediate (SSP2-4.5) and very high emissions (SSP5-8.5) were combined with nutrient load reductions according to the National Water Plans to investigate potential impacts on natural benthic mussel populations and suspended mussel culture for the two periods 2051-2060 and 2090-2099, relative to a reference period from 2009 to 2018. The FlexSem model combined 3D hydrodynamics with a pelagic biogeochemical model, a sediment-benthos model, and a dynamic energy budget - farm scale model for mussel culture. Model results showed that the Limfjorden was sensitive to climate change impacts with the strongest responses of physics and water quality in the worst case SSP5-8.5 scenario with no nutrient reductions. In the two low emissions scenarios, expected improvements of bottom oxygen and Chlorophyll a concentrations due to reduced nutrient loads were counteracted by climate change impacts on water physics (warming, freshening, stronger stratification). Hence, higher nutrient reductions in the Water Plans would be needed to reach a good ecological status under the influence of climate change. Suspended mussel culture was intensified in all scenarios showing a high potential harvest, whereas the benthic mussels suffered from reduced food supply and hypoxia. Provided the environmental changes and trends in social demands, in the future, it is likely that suspended mussel cultivation will become the primary source of mussels for the industry. Model scenarios can be used to inform managers, mussel farmers, fishermen, and the local population on potential future changes in bivalve harvesting and ecosystem health, and to find solutions to mitigate climate change impacts.

Keywords: Biogeochemical cycles; Chl a; Ecosystem model; Eutrophication; Low-trophic aquaculture; Oxygen.