Combined effects of global climate change and regional ecosystem drivers on an exploited marine food web

Abstract

Changes in climate, in combination with intensive exploitation of marine resources, have caused large-scale reorganizations in many of the world's marine ecosystems during the past decades. The Baltic Sea in Northern Europe is one of the systems most affected. In addition to being exposed to persistent eutrophication, intensive fishing, and one of the world's fastest rates of warming in the last two decades of the 20th century, accelerated climate change including atmospheric warming and changes in precipitation is projected for this region during the 21st century. Here, we used a new multimodel approach to project how the interaction of climate, nutrient loads, and cod fishing may affect the future of the open Central Baltic Sea food web. Regionally downscaled global climate scenarios were, in combination with three nutrient load scenarios, used to drive an ensemble of three regional biogeochemical models (BGMs). An Ecopath with Ecosim food web model was then forced with the BGM results from different nutrient-climate scenarios in combination with two different cod fishing scenarios. The results showed that regional management is likely to play a major role in determining the future of the Baltic Sea ecosystem. By the end of the 21st century, for example, the combination of intensive cod fishing and high nutrient loads projected a strongly eutrophicated and sprat-dominated ecosystem, whereas low cod fishing in combination with low nutrient loads resulted in a cod-dominated ecosystem with eutrophication levels close to present. Also, nonlinearities were observed in the sensitivity of different trophic groups to nutrient loads or fishing depending on the combination of the two. Finally, many climate variables and species biomasses were projected to levels unseen in the past. Hence, the risk for ecological surprises needs to be addressed, particularly when the results are discussed in the ecosystem-based management context.

Controls of Multiple Stressors on the Black Sea Fishery

“…The current ecosystem models are presently not coupled with the carbonate chemistry to investigate the acidification problem under synergistic effects of climate change and eutrophication. How the Black Sea ecosystem might respond to future changes in climate in combination with other drivers appears to depend on characteristics of other stressors (Niiranen et al, 2013). Preliminary studies have been conducted by Cannaby et al (2015) but a deeper analysis under different scenarios of stressor combinations (different combinations of fishing and nutrient load management scenarios) are worthwhile to perform.…”

“…Coastal, shelf, and semi-enclosed seas providing important economic resources experience additional stressors arising from the local/regional natural climatic variations, eutrophication, eutrophication-induced changes (such as acidification, de-oxygenation, loss of biodiversity, degradation of food web, etc), overfishing, and alien species invasion (Boldt et al, 2014). For these ecosystems, both CO 2 and non-CO 2 related stressors acting together have potential to alter trophic structure, food-web dynamics, energy and material flows, and biogeochemical cycles and thus impact considerably the ecosystem services for humans, as in the case of Baltic Sea (Niiranen et al, 2013;Jutterström et al, 2014). The Black Sea offers one of the best examples for how the multiple stressors act together to alter its ecosystem structure through regime shifts (Daskalov et al, 2007;Oguz and Gilbert, 2007;Oguz and Velikova, 2010;Llope et al, 2011;Akoglu et al, 2014).…”

Past and future challenges in managing European seas

“…Besides temperature-induced changes, salinity in semienclosed seas, like the Baltic Sea, can be of major importance for species distribution. Meier et al (2012) projected a significant lower salinity and deep-water oxygen concentrations until 2100, which may lead to a shift from marine to more brackish or even freshwater species, negatively affecting the abundance of commercially important fish species, such as cod (Niiranen et al 2013). Also, in the Mediterranean and Black Seas, endemic species may disappear, and there is a high risk that associated niches will probably be filled by species originating from adjacent waters (Philippart et al 2011).…”

Effects of ocean acidification on pelagic carbon fluxes in a mesocosm experiment

“…Human activities (e.g., agriculture, shipping, and fishing) cause a number of environmental problems such as eutrophication and pollution. As a coastal sea projected to change rapidly due to interaction of direct and indirect anthropogenic pressures, the Baltic Sea can be seen as a model ecosystem for studying global change scenarios (Niiranen et al, 2013).…”