There is now indisputable evidence that the planet is experiencing a period of rapid climate change, mainly driven by anthropogenic activities. The three European seas investigated in VECTORS, the Mediterranean Sea, the Baltic Sea and the North Sea, have all undergone continuous warming during the second half of the twentieth century.
The Intergovernmental Panel on Climate Change (IPCC) recently concluded with ‘high confidence’ that due to projected climate change by the mid-21st century and beyond, global marine-species redistribution and marine-biodiversity reduction in sensitive regions will challenge the sustained provision of fisheries productivity and other ecosystem services1.
Climate change has led to sea level rise2, and alters sea water salinity, biogeochemistry, UV radiation, as well as atmospheric and hydrographic circulation patterns, and causes ocean acidification. More frequent extreme weather events have been predicted for Europe, and coasts have been expected to be exposed to increasing risks3. Climate change is considered to be a major threat to biodiversity as well as to ecosystem structure and functioning, thereby also affecting marine resources and global fisheries potential4.
Marine ecosystems are vulnerable to climate change as several key processes are governed by temperature. A notable advance of warm-water adapted organisms against the retraction of cold water species has occurred in several European seas5. Climate change has various implications for marine fish, including direct mortality of sensitive life stages and alterations in transport of fish larvae to their nursery grounds, which may lead to a mismatch between the timing of reproduction and to the occurrence of prey6. Generally, intense fishing is expected to increase the vulnerability of fish populations to climate effects.
Overall, the increase in temperature has been higher in northern than in southern European seas, and higher in enclosed than in open seas7. For the Mediterranean, as a semi-enclosed system, a big concern is a possible loss of endemic species through competition with species introduced through shipping via ballast water or directly through the Suez Canal.
In the Baltic Sea, overfishing of cod has during previous decades amplified climate-induced changes in zooplankton and fish communities. In regions most enclosed, river runoff from increased rainfalls could support a shift from marine to more brackish and even freshwater species.
The North Sea ecosystem has been through phases of different climatic conditions over the last 50 years, distinguished by the amount of Atlantic inflow. In recent decades, warming has led to elevated abundances of Lusitanean (southern European) species and to a shift in the seasonal occurrences of key species, which has resulted in a mismatch in traditional predator-prey interactions and also contributed to a low recruitment of cod.