Sea urchins and kelp forests
Sea urchins are found all along the Norwegian coastline. In Norway, there are 16 different species. Sea urchins are echinoderms in the class Echinoidea. The term echinoderm comes from the Greek words for “hedgehog” and “skin” – quite the fitting name. In Norway, the most common sea urchins are the red-coloured European edible sea urchin (Echinus esculentus) and the green sea urchin (Stronglyocentrotus droebachiensis).
Sea urchins are easily recognizable. Most are round, some more oval or disc-shaped, and all have distinct spikes. The spike length and thickness vary according to species, and the sea urchins can move the spikes individually.
Sea urchins are mostly found in shallow waters, but they have been found down to depths of approximately 1,200 metres. They prefer hard bottoms.
Kelp, sea grass and diatoms are the sea urchins’ preferred food, but they can also eat barnacles and other animals.
Photo: Geir Eliassen.
In the last decades there has been a large increase in sea urchin numbers. Experts have not been able to determine why, but it is assumed to be because of overfishing of the fish species that prey on sea urchins. This population boost has led to an increase in kelp forest grazing, which in turn could be a cause for concern. Along the entire coast of Northern Norway, especially in sheltered areas, overgrazing has led to larger areas of bare rock – rock that was previously covered by kelp forests.
Disappearing kelp forests affect the animals living there, among which are crustaceans, bristle worms and molluscs. These small animals are food for larger animals, and thus important links at the bottom of several food chains. The disappearance of these animals would therefore lead to a disruption in the energy transfer further up in the food chain. This in turn creates a domino effect that can affect us humans directly, for instance through a negative impact on the fishery industry.
In addition, kelp forests are especially important for the climate. The kelp forests both bind large amounts of CO2, as well as produce oxygen – they are at least as important as the tropical rainforests on land.
Photo: Stein Fredriksen / Institute of Marine Research