Abstract
The responses of food webs to simultaneous changes in several environmental drivers are still poorly understood. As a contribution to filling this knowledge gap, we investigated the major pathways through which two interlinked environmental drivers, eutrophication and climate, affect the biomass and community composition of fish and benthic macrofauna. For this aim, we conducted a systematic sensitivity analysis using two models simulating the dynamics of benthic and pelagic food webs in the Baltic Sea. We varied environmental forcing representing primary productivity, oxygen conditions and water temperature in all possible combinations, over a range representative of expected changes during the 21st century. Both models indicated that increased primary productivity leads to biomass increase in all parts of the system, however counteracted by expanding hypoxia. Effects of temperature were complex, but generally small compared to the other drivers. Similarities across models give confidence in the main results, but we also found differences due to different representations of the food web in the two models. While both models predicted a shift in benthic community composition towards an increased abundance of Limecola (Macoma) balthica with increasing productivity, the effects on deposit-feeding and predatory benthic groups depended on the presence of fish predators in the model. The model results indicate that nutrient loads are a stronger driver of change for ecosystem functions in the Baltic Sea than climate change, but it is important to consider the combined effects of these drivers for proper management of the marine environment.
Highlights
Marine ecosystems are threatened by multiple anthropogenic pressures (Halpern et al, 2008)
oxic areas (OxAr) had a positive effect on cod (Figure 3A) and L. balthica (Figure 3E), due to their increased consumption of benthic food
We have used two distinct food web models to study the effects of environmental drivers on marine ecosystem components in the Baltic Sea
Summary
Marine ecosystems are threatened by multiple anthropogenic pressures (Halpern et al, 2008). Climate change affects the life-histories and distributions of marine species, and is recognized as a major driver of food-web reorganizations (Poloczanska et al, 2013; Cloern et al, 2016). Process-based ecological models are powerful tools to conduct such tests (Christensen and Walters, 2004; Coll et al, 2015; Seidl, 2017). Such models can be used to study the relative importance of direct (e.g., physiological) and indirect (e.g., food-web mediated) effects on ecosystem components (Blackford, 2002; Fulton et al, 2004; Condie et al, 2012)
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