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 less and less in the wild. The iconic cod (Gadus morhua) is a typical structure loving species. Having suffered much from over-fishing, cod can still be found in low numbers around the North Sea basin. With larger individuals being more prone to be fished out, most cod don't reach their potential size anymore; with an average of 1m and large females even able to reach 2m length!
Cod are a migratory species, moving between feeding and spawning grounds. Juveniles prefer the shallower coastal waters up to 30m, with larger adults moving to deeper waters of 200m and beyond. They are a cold water species, prefering temperatures below 20*C and below, making them vulnerable to climate change. They are opportunistic omnivors, eating continuously as juveniles and during dusk and dawn as adults. Cod are often found around man-made structures such as platforms and shipwrecks.

(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.