Species

Known for its vibrant colors and large claws, the European lobster (Homarus gammarus), the largest crustacean of the North Sea. This impressive animal can grow up to 50cm and live up to 20 years. After reaching maturity between 4 and 10 years old, the lobster grows very slowly, shedding its armour to be replaced with a larger one. Lobsters are mostly nocturnal animals, spending their evenings looking for smaller shellfish and worms. They’ll also eat small fish and algae, if it’s on the menu! When lobsters are still small, they can be a food source for species including cod or dogfish (small sharks).

Lobsters love to live in complex habitats with different structures and surfaces. They set up homes around hard substrates, holes, and crevices. For food collection and nursery areas, they prefer softer surfaces such as sand and mud. Juveniles may shelter communally, while adults prefer the solitary lifestyle. They use and guard their burrows during vulnerable times, like molting, and can dig themselves inside for weeks at a time during the winter.

Well-known on the plate, but diminishing in the wild, the iconic cod (Gadus morhua) is a typical structure-loving species. Cod are a migratory species often found around man-made structures, like platforms and shipwrecks. Juveniles prefer the shallower coastal waters up to 30 meters, with larger adults moving to deeper waters of 200 meters and beyond. This cold water species prefers temperatures below 20°C, which makes them vulnerable to climate change.

Having suffered much from over-fishing, cod can still be found in low numbers around the North Sea basin. As larger individuals are more prone to be fished out, most cod don’t reach their maximum size anymore. Male cods can grow up to one meter long, and females can reach two meters!

(Image by OCEANA)

The blue or common mussel (Mytilus edulis) is a well-known resident of the North Sea. This filter-feeding reef builder is sturdy, adapting to many different conditions and turbulent waters. Mussels live on hard surfaces such as rocks, man-made objects, and even each other! To survive, larvae must attach to a suitable settlement substrate. Blue mussels can cluster into ‘beds,’ forming habitats for many other species. Along with providing living spaces, these small critters can also filter water and influence the carbon cycle by depositing their pseudofeaces. They’re also a favorite food of birds, star fish, crabs – and humans!

Blue mussels are mostly found near shores and up to a few meters below the low water mark. However, they are also present on farther-out structures such as platforms, buoys, and wind turbines (mostly in the upper part of the water column). Mussels also appear on wrecks and scour protection, which proves their resilience and potential to survive in deeper North Sea areas.

Native to the North Sea, the European flat oyster (Ostrea edulis) is known for its ability to create reefs that attract a diverse range of marine life. These oysters can cluster together to form rich biodiversity hubs where species like goldsinny wrasse, cod, and spotted catshark thrive. In these vibrant ecosystems, sponges, tubeworms, hydroids, anemones, and crustaceans also find a home.

Did you know that the European flat oyster can also change its sex? As a so-called ‘protandrous hermaphrodite’, oysters start their spawning season as a male and later change to female. This can even happen within the same season! Under the right circumstances, a female oyster can hold up to one million fertilized eggs. Once the larvae are released (after eight to ten days), they have another sprint of eight to ten days to find a suitable place to settle. This relatively short mobile phase means that the dispersal of flat oysters is limited as well – spanning from zero to ten kilometres.

The ross worm (Sabellaria spinulosa) is a polychaete tubeworm species that constructs small tubes from sand or shell fragments. They are usually found on hard substrate, where sand is available for tube building. Over the majority of its distribution, Ross worms are found individually or in small groups. However, in large numbers, the tubes formed by Ross worms can become their own reef. These reefs can grow several hectares wide and up to 60 centimeters high. Like skyscrapers, the height is achieved when there is competition for space, resulting in tubes built high away from the substrate.

Once a worm is detached from its settlement substrate, it cannot build a new tube. This makes them sensitive to displacement that occurs from stormy weather and activities like dredging, trawling, and infrastructure installation. Thanks to the team spirit of these worms, their recovery potential is high due to fast colonization.

(Image by OCEANA)

This fishy friend is known by many names: bib, pout, pout whiting or pouting (Trisopterus luscus). Although part of the cod family, this saltwater fish won’t grow quite as big as its cousins, as adults are an average size of 20 to 30 centimeters (and up to 45cm). Pout typically have three or four vertical pale bands across their darker-colored body, but larger adults may lose the bands entirely.

Another pout marker is a black spot (about the size of their eye) at the base of their pectoral fin. Juvenile pout prefer to travel in groups, and occur in large schools. To locate prey like crustaceans, small fish, molluscs, and polychaetes (worms), pout will use their well-developed chin barbel.

The sand mason worm (Lanice conchilega) is a polychaete worm which makes a tube out of sand grains and shell fragments. It is typically sand colored with yellow, pink, or brown hues, and has three pairs of blood red bushy gills. This worm uses small white tentacles to trap particles of food, deposit feeding, or suspension feeding depending on density. Larvae can spend up to 60 days in a water column before settling down, giving this species potential for great spatial distribution. Larvae may settle in areas where adult sand mason worms are already present, or colonize new locations. They can be found individually or in thousands, forming structures which can increase species richness.