Combined Effects of Environmental Drivers on Marine Trophic Groups – A Systematic Model Comparison

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 toward 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.

The meagre future of benthic fauna in a coastal sea—Benthic responses to recovery from eutrophication in a changing climate

“…Also Saraiva et al (2019) The larger biomass decreases in climate change scenarios compared to current climate can be explained by the combined effects of reduced input of organic matter as food, faster degradation of the food banks and increased metabolism due to warmer temperatures. In a previous systematic sensitivity analysis using BMM, we found quite small effects of temperature on macrofaunal biomass compared to the effects of POC input (Ehrnsten, Bauer, et al, 2019).…”

“…The long‐term and seasonal dynamics of BALTSEM have been validated previously (see model description). Ehrnsten, Norkko, et al () validated BMM against time‐series of macrofauna biomass in two coastal sites of the Baltic Sea, and Ehrnsten, Bauer, et al () studied the sensitivity of the model to changes in temperature, organic matter sedimentation rate and oxygen conditions.…”

“…Previously, Timmerman et al () estimated the balance between biomass lost and gained with changes in nutrient loading at six stations in the deeper parts of the Baltic Sea using a physiological macrofauna model driven by outputs from a physical–biogeochemical model, but did not investigate the effects on carbon cycling. This model was further developed to simulate the biomass and metabolic carbon processing of benthic fauna in two coastal areas in the near past (Ehrnsten, Norkko, Timmermann, & Gustafsson, ) and to systematically investigate the effects of temperature, food supply and hypoxia on local benthic communities in the Baltic Proper (Ehrnsten, Bauer, & Gustafsson, ). Here, we extend these developments to explore the response in biomass and metabolic carbon processing of benthic macrofauna to the combined effects of different scenarios of changing nutrient loads and climate on the scale of the Baltic Sea over a century.…”

Understanding Environmental Changes in Temperate Coastal Seas: Linking Models of Benthic Fauna to Carbon and Nutrient Fluxes

“…Evidently, mechanistic models are useful tools to quantitatively study the biogeochemistry of coastal ecosystems and to tackle managements questions such as the relationships between nutrient inputs, human interventions (e.g., restoration, constructions, shellfish farming) and the nutrient filtering capacity or ecological state of the ecosystem. Such models also have great potential to investigate the influence of climate change on coastal benthos (Thomas and Bacher, 2018;Ehrnsten et al, 2019a) and the role of coastal ecosystems as sources or sinks for greenhouse gases (Sohma et al, 2018). Isaev et al (2017) also demonstrate how an ecosystem model can be used to study the combined impact of climate change and invasion of a bioturbating species on coastal nutrient fluxes.…”

Effects of Nutrient Management Scenarios on Marine Food Webs: A Pan-European Assessment in Support of the Marine Strategy Framework Directive

“…The reason why these systems responded differently to a reduction in nutrient load is probably because the level of eutrophication observed in the Baltic Sea is worse than in other regional seas, as shown also by McQuatters-Gollop et al (2009), and oxygen is one of the main ecosystem drivers (Ehrnsten et al, 2019) thus, the system is more prone to improve, even if little as in this case, than the others. Theoretical studies suggest that an increase in species diversity might occur when productivity shifts from high (eutrophic) to intermediate levels and predator and/or fishing pressure stays low to medium (Kondoh, 2001;Worm et al, 2002).…”