Marine food webs describe the linkages between all living organisms found in the marine environment, where every plant and animal species depends on another plant or animal species for its survival. This interdependency can be explored in predator–prey relationships or food chains.
Individual food chains operate within much larger and more complex networks called food webs. Food webs regulate the ecosystem dynamics, and play an essential role in the way ecosystems respond to natural and human-induced changes.
Slight changes in the state of one species can have cascade effects and produce dramatic changes in an entire ecosystem and the food web dynamics. They are referred to as ecological regime shifts, and several have been observed in a number of Europe's regional seas over the past century. Since the late 1980s, climate-caused regime shifts may have made the seas less resilient to other anthropogenic pressures influencing each regional sea, thereby contributing to the patterns of change that have been subsequently observed.
There is currently a lack of consistent approach to assess the state of food webs across Europe’s seas with many assessments considered incomplete and associated with high uncertainty due to lack of suitable data. However, while the overall state of marine food webs across all European seas cannot be fully assessed, there are many examples of trophic guilds showing deteriorating trends over time, probably being affected by anthropogenic pressures (e.g. fishing, climate change or habitat destruction). This especially concerns the reductions in abundance of several top predators, such as birds, sharks and marine mammals.
General outcomes of the regional assessments
While the assessment of the state of food-webs in Europe’s seas is complex, there are various national level indicators which show trends on state of food webs or in food web recovery which can be attributed to the implementation of key EU and other policies.
For example in the North-east Atlantic Ocean long-term changes in zooplankton composition observed through the Continuous Plankton Recorder have been used to assess shifts in ecosystem function and dynamics. The assessment shows that the copepod community of the Celtic and Greater North Seas has changed from cold water species to warm water species between 1960 and 2000. This shift has been observed to impact the growth, recruitment and survival of other trophic levels e.g. fish.
In the Baltic Sea indicators of biomass of zooplankton and zooplankton/phytoplankton ratios have been used to assess environmentally driven changes in the food web and possible impacts of eutrophication.There is evidence of a shift in the functioning of the central Baltic Sea ecosystem during the last 3 decades (Casini et al 2009), in particular from a cod dominated system to a sprat-dominate system.
In the Black Sea the keystone index has shown a shift from top-down control system dominated by dolphins between 1960 and 1969 but a bottom-up control between 1988 and 1994 dominated by jellyfish.
Outcomes from the MSFD assessments
In 2018, Member States had to update the Good Environmental Status (GES) assessments performed under Marine Strategy Framework Directive Article 8. The present dashboard displays the overall status reported by countries for the features, where the results show which is the percentage of assessments where GES has been achieved, not achieved or is unknown or not assessed.