Modeling eelgrass spatial response to nutrient abatement measures in a changing climate

Abstract

For many coastal areas including the Baltic Sea, ambitious nutrient abatement goals have been set to curb eutrophication, but benefits of such measures were normally not studied in light of anticipated climate change. To project the likely responses of nutrient abatement on eelgrass (Zostera marina), we coupled a species distribution model with a biogeochemical model, obtaining future water turbidity, and a wave model for predicting the future hydrodynamics in the coastal area. Using this, eelgrass distribution was modeled for different combinations of nutrient scenarios and future wind fields. We are the first to demonstrate that while under a business as usual scenario overall eelgrass area will not recover, nutrient reductions that fulfill the Helsinki Commission's Baltic Sea Action Plan (BSAP) are likely to lead to a substantial areal expansion of eelgrass coverage, primarily at the current distribution's lower depth limits, thereby overcompensating losses in shallow areas caused by a stormier climate.

Climate Change in the Baltic Sea Region: A Summary

“…Using only one climate scenario, Bonaduce et al (2019) found that decreased wind speed in the southern Baltic Sea led to a decrease in mean SWH, whereas increased wind speeds in the north, especially in winter, led to increased mean SWH. As neither study used multi-model ensembles of scenario simulations (an exception for the western Baltic Sea is the work by Dreier et al (2021), and there is high uncertainty in the projected wind speeds and directions, which is not attributed to the decline in ice cover, the results may not be representative. The projected changes in SWH estimates are therefore inconclusive.…”

“…Overall, it is expected that climate change and its interaction with other environmental factors (e.g. eutrophication) will cause complex responses and influence carbon storage in both macroalgae and vascular plants in the Baltic Sea (Jonsson et al, 2018;Takolander et al, 2017;Röhr et al, 2016;Perry et al, 2019;Salo et al, 2020;Bobsien et al, 2021).…”

“…Species distribution modelling has indicated that a decrease of bladder wrack will have large effects on the biodiversity and functioning of the shallow-water communities of the northern Baltic Sea (Jonsson et al, 2018;Kotta et al, 2019). The responses of eelgrass, Zostera marina, to climate change and eutrophication mitigation have recently been modeled by Bobsien et al (2021).…”

Global climate change and the Baltic Sea ecosystem: direct and indirect effects on species, communities and ecosystem functioning

“…A study performed for the southernmost Baltic Sea coupled species distribution and biogeochemical modelling to project how projected wind fields, hydrodynamic conditions and nutrient abatement scenarios affect the distribution of eelgrass Zostera marina in the future (2062)(2063)(2064)(2065)(2066). It was concluded that nutrient reductions that fulfill the Helsinki Commission's Baltic Sea Action Plan (BSAP) will lead to an expansion of eelgrass coverage, despite potentially harmful effects on eelgrass distribution caused by a projected stormier climate (Bobsien et al, 2021). The rapidly changing marine environment in the https://doi.org/10.5194/esd-2021-73 Preprint.…”

“…Overall, observations of past changes, experimental work and modelling studies suggest that climate change can cause complex responses in relation to other environmental factors (e.g. eutrophication) and influence carbon storage in both macroalgae and vascular plants in the Baltic Sea (Jonsson et al, 2018;Takolander et al, 2017a;Röhr et al, 2016;Salo et al, 2020;Bobsien et al, 2021).…”