The North Sea, a shallow arm of the Atlantic Ocean, lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. Covering an area of approximately 570,000 to 750,000 square kilometers, it is a significant body of water on the European continental shelf. Its average depth is about 95 meters, though it plunges to a maximum of 725 meters in the Norwegian Trench, which runs parallel to the Norwegian coastline. This dynamic marine environment is one of the world’s most productive seas, supporting a wide array of life from microscopic plankton to large marine mammals.
Fish Species
The North Sea supports a diverse range of fish species, including those that dwell on the seabed, known as demersal fish, and those that inhabit the open water column, referred to as pelagic fish. Many of these species hold significant commercial value and form important parts of the marine food web. Over 230 species of fish live in the North Sea.
Demersal fish commonly found in the North Sea include cod, haddock, plaice, and sole. Other bottom-dwelling species include whiting, monkfish, and hake. These fish often feed on invertebrates found on or in the seabed and sometimes on smaller fish.
Pelagic fish species are also abundant. Prominent examples include herring, mackerel, and sprat. Blue whiting and horse mackerel are also important pelagic species. These fish feed on plankton and smaller organisms, forming a crucial food source for larger predators in the North Sea ecosystem.
Marine Mammals
The North Sea is home to a variety of marine mammals, with both resident populations and occasional visitors. Two common seal species found here are the harbor seal and the grey seal. Grey seals are particularly prevalent along British coasts.
Among cetaceans, the harbor porpoise is the most abundant species in the North Sea. Minke whales and white-beaked dolphins are also commonly sighted, particularly in the central and northern parts of the sea. Bottlenose dolphins inhabit areas like the eastern British coast and the Moray Firth, with their populations showing an increasing trend in some regions. Killer whales are regularly observed in the northern North Sea, and humpback whales have been increasingly recorded, even in the southern North Sea where they were previously rare.
Seabirds of the North Sea
The North Sea provides essential feeding grounds and habitats for numerous seabird species, with many relying on its rich marine life for sustenance. Around 10 million seabirds are present in and around the North Sea at various times of the year. Gulls, such as herring gulls, are commonly seen, though they are more coastal birds.
True seabirds include species like kittiwakes, guillemots, and razorbills. These birds often nest in large colonies on rocky coasts and cliffs in areas like Scotland, northern England, and Norway. Puffins, known for their distinctive appearance, also breed in burrows on grassy clifftops.
Other prominent seabirds include gannets, which are the largest seabirds in the region with wingspans of up to two meters, and fulmars. Gannets are known for their spectacular plunge-diving technique to catch fish. Skuas, which are often observed stealing food from other seabirds, also frequent the area. These birds primarily feed on fish and invertebrates, diving or surface-feeding depending on their species.
Invertebrates and Benthic Creatures
The seabed of the North Sea, particularly its sandy and silty areas, hosts a vast array of invertebrates and benthic creatures, which are organisms living on or within the bottom sediments. These organisms form a fundamental part of the marine food web. The North Sea is home to diverse benthic communities, with species distribution often influenced by sediment type and water depth.
Crabs, such as the edible crab, and lobsters are common crustaceans found crawling across the seabed or hiding among stones. Various species of starfish, including the common starfish, are also prevalent, often acting as scavengers. Shellfish like mussels, oysters, and clams live burrowed in the sediment, filtering nutrients from the water through their siphons.
Jellyfish, such as the moon jellyfish, drift through the water column, while sea anemones, like Metridium senile, attach themselves to hard surfaces on the seabed. Different types of worms, including rag-worms and tube-dwelling worms, burrow through the sand and mud, contributing to the aeration and nutrient cycling of the sediments. Barnacles, a group of crustaceans, are also common, spending their adult lives attached to rocks and other submerged structures.