North Sea ecosystem

• Category: Marine and Oceanic Biomes.
• Geographic Location: Europe.
• Summary: This ecologically rich North Atlantic basin is the nautical corridor connecting northern Europe ecosystems with the wider seas.

The North Sea is a semi-closed, continental-fringe sea in the North Atlantic Ocean. Given its strategic position as a doorway to the Atlantic, it has had a major part in shaping European history—and this has heavily affected its ecology. Commercial productivity of the region lies mainly in its fisheries, hydrocarbon fuels, and renewable energy. Conservation is also of the utmost importance, with many of Europe’s most valuable natural habitats occurring around its perimeter.

The North Sea lies between Great Britain and the coastline of continental Europe, with Norway at its northern extremity and France to the south. It is the only marine interface for Belgium and the Netherlands, and also a major component of the marine territory of Great Britain, Germany, Denmark, Sweden, and Norway. It spans approximately 289,577 square miles (750,000 square kilometers); and its gently sloping topology is shallowest in the south, typically around 164 feet (50 meters) deep, reaching 328 feet (100 meters) in the center of the basin, and more than 2,297 feet (700 meters) in the Norwegian Trench.

Scattered throughout the basin are several large sandbanks, including the Dogger Bank, the Broad Fourteens, and the Deep Forties. With an area of approximately 6,795 square miles (17,600 square kilometers), the Dogger Bank is one of the most productive fishing grounds in the North Sea.

Current flow tends to be counterclockwise, with the greatest inflow entering via the Norwegian Sea. The circulation of the North Sea is influenced by strong tidal variations. The large-scale surface currents are mainly driven by the wind. They follow a counter-clockwise flow direction. Atlantic water also enters via the English Channel, but this flow is somewhat more restricted. Brackish water also infiltrates the North Sea from the Baltic Sea via the Kattegat and Skagerrak. The salinity and temperature of North Sea waters fluctuate with the North Atlantic Oscillation.

Species and Biomass

The North Sea has an extremely diverse coastal extent, including fjords, sandbanks, mudflats, large estuaries, and deltas, but the seabed itself is mostly sandy or muddy. There is a general pattern of increased species richness around the circumference of the North Sea. A variety of invertebrates are found on the North Sea benthos, including polychaete worms, sea urchins, brittle stars, shrimp, and lobsters.

Extensive beds of coldwater coral Lophelia have been mapped along the shores of Norway, particularly along the Norwegian margin of the Skagerrak, where a unique yellow variety has been recorded. Sabellaria reefs are also known to exist, although their distribution has yet to be fully studied. Sabellaria spinulosa reefs are rare and typically found in areas with high suspended sediment in the North Sea, making their full extent difficult to assess. A 2017 expedition revealed the unexpected presence of living Sabellaria reefs in Dutch waters, previously believed to have disappeared due to overfishing and human activity. These reefs were found in multiple locations on Brown Bank, an ecologically significant area in the southern North Sea. Brown Bank supports a diverse range of marine life, including cetaceans, seabirds, and commercially important fish species like cod and herring. However, it faces significant threats from human activities such as bottom fishing, wind energy development, oil and gas exploitation, and ship traffic, which harm its biodiversity and ecosystems. They are listed under Annex I of the European Habitats Directive, the United Kingdom's Biodiversity Action Plan, as threatened habitats.

The pelagic fish community is dominated by herring, with summer peak abundances in mackerel and horse mackerel. Cod, haddock, whiting, and saithe are also important, in addition to flatfish such as sole and dab. The relative abundance and distribution of fish varies from year to year in accordance with climatic conditions. At the beginning of the twenty-first century, highly migratory species such as tuna and halibut that once were abundant became rare, although sightings increased since 2014 and some enormous halibut have been caught in the 2020s.

In the 1930s, the North Sea hosted a popular bluefin tuna fishery, but it collapsed by the 1950s due to overfishing, and sightings became rare. By the 1990s, bluefin tuna had largely disappeared from the North Sea. However, after the International Commission for the Conservation of Atlantic Tunas (ICCAT) launched a recovery plan in 2007, bluefin tuna populations began to rebound, and sightings in UK and Irish waters resumed by 2010. By the mid 2020s, bluefin tuna were commonly seen in the North Sea. Bluefin tuna were removed from the IUCN Red List of Endangered species in 2021 and were reclassified as a species of Least Concern. While the species has been removed from the IUCN Red List, caution is needed to manage commercial and recreational fishing to prevent overfishing and ensure sustainable populations as tuna numbers continue to recover.

Although overfishing is often blamed for the disappearance of many fish species, scientists also suspect that climate change has also had major impacts on the food chain in the North Sea, reducing the food supply for larger sea creatures.

The basin is a key ecosystem for seabirds, and around five million birds of twenty-eight bird species breed in the area each year. These birds occupy niches from surface feeders to divers and waders. Foraging expeditions can range over hundreds of miles (kilometers) at a time. Many of these seabirds interact with fisheries in the area through competing for resources and consuming discards.

Marine mammals in the North Sea tend to be transient, with a few resident populations of harbor and gray seals, occurring particularly along the British coast. Seals compete for resources with fishing boats and commonly depredate passive fishing gear. Three main marine mammal species frequent this sea: minke whales, white-beaked dolphins, and harbor seals. Minke whales tend to remain in the northern reaches of the sea, while dolphins are more abundant in the south, and it is thought that the North Sea may be the most important habitat in the world for these animals.

Resources

The commercial and recreational value of the North Sea basin is considerable, especially in terms of fishing and boating. It is also a major conduit for freight ships, military vessels, and underwater cables. Considerable oil and gas deposits lie beneath the North Sea. For this reason, the area has attracted investment from the world’s energy producers. Several European states now have well-established operations within the basin, including Belgium, Denmark, France, Germany, the Netherlands, Norway, and the United Kingdom (UK).

European nations have been harnessing wind power in the North Sea since the early 1990s. One of the world’s largest offshore facilities, the Thanet wind farm, was inaugurated in 2010 and is located close to the shore of southeast England. Projects established in the Scottish Orkney Isles are generating wave and tidal energy. Plans are under way to establish an electricity supergrid connecting renewable energy resources from across the North Sea area. The 1.8 billion British pound (£) Viking Link project, launched in 2024, will connect the UK and Denmark. It will have a capacity of 1.4 gigawatts (GW), powering up to 2.5 million UK homes. The project will be the longest land and subsea cable in the world. The project is expected to deliver 5.2 billion Bitish pounds in benefits to UK consumers and will play a key role in both the UK and Denmark's efforts to achieve net-zero carbon emissions by facilitating renewable energy sharing.

Conservation Efforts

European waters are conserved through several international policies, including the Habitats Directive and the Birds Directive. Numerous locations have been designated as Natura 2000 sites to meet the objectives of these two directives, while the Ramsar Convention designates wetlands of international importance, and other conventions aim to establish a network of marine protected areas.

Perhaps the most important region of conservation interest is the Wadden Sea, which follows 311 miles (500 kilometers) of coast from the northern reaches of the Netherlands, along the German shoreline, to the western seaboard of Denmark. Its extensive mudflats provide important habitat for seabirds and shorebirds, and rich feeding grounds for migratory species. It is an immensely valuable ecosystem because of its rich diversity, and part of the Wadden Sea is now listed as a World Heritage Site.

Bibliography

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