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

  • ️Mon Jan 01 2024

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

Marie Maar et al. Heliyon. 2024.

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.

© 2024 The Authors.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1

Map showing A) the location of the Limfjorden (red box) and B) surface salinity (color bar), mussel farms (cyan points), and names of the main basins; Nissum Broad (Nissum), Sallingsund (Sall.), Thisted Broad (Thisted), Løgstør Broad (Løgstør), Skive Fjord (Skive), and Nibe Broad (Nibe). Grey hatched lines are the Natura 2000 areas where mussel farming is not allowed. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2
Fig. 2

Mussel harvest from aquaculture and mussel landings from fishery in the Limfjord area (Data from the Fishery Agency).

Fig. 3
Fig. 3

Forcing data showing annual means (±SD) for each period of A) air temperature, B) precipitation, C) summer wind speed, D) run-off, E) TN river load, and F) TP river load. Values above the columns are the percentage differences from the reference period 2009–2018.

Fig. 4
Fig. 4

Summer (June to September) means (±SD) of A) sea surface salinity (SSS), B) sea surface temperature (SST), C) stratification index (PEA), D) hypoxic area (<4 mg l−1) as percentage of total area, E) surface Chl a concentration, and F) benthic mussel biomass for the reference period (2009–2018) and the three scenarios and the two time-slices 2051–2060 and 2090–2099. The values above the columns are the percentage deviations from the reference period. The horizontal dashed line in E) indicates the thresholds for a good ecological status (GES).

Fig. 5
Fig. 5

Spatial plots showing the difference of physical variables between the three scenarios (years 2090–2099) and the reference (years 2009–2018) for the summer period. A-C) surface salinity, D-F) surface temperature, and G-I) stratification index for the scenarios SSP1-2.6 (1st column), SSP2-4.5 (2nd column), and SSP5-8.5 (3rd column).

Fig. 6
Fig. 6

Spatial plots showing the difference of ecosystem variables between the three scenarios (years 2090–2099) and the reference (years 2009–2018) for the summer period bottom. A-C) bottom oxygen, D-F) surface Chl a concentrations, and G-I) benthic mussel biomass for the scenarios SSP1-2.6 (1st column), SSP2-4.5 (2nd column), and SSP5-8.5 (3rd column).

Fig. 7
Fig. 7

Annual means (±SD) of A) mussel harvest from suspended farms and B) mussel shell length in the scenarios indicated with percentage changes from the reference period 2009–2018. See Fig. 4 for further explanation.

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