Green sea urchin
Sea urchins have a hard and rigid exoskeleton. They are also covered with spines for protection. They are grazers or detritus feeders.
Two species of echinoderms have been harvested in Icelandic waters, green sea urchin and sea cucumber (Cucumaria frondoze). Both are large and relatively abundant all around the country.
Usually the green sea urchin is a peaceful animal, crawling slowly along the bottom and scavenging on dead kelp and detritus from the bottom. However, it is known from several localities in the world that they can behave like a locust plague in slow motion if they are in great numbers. Then the behaviour changes and they start climbing up the kelp stipe and eat the kelp alive.
This has happened in Eyjafjörður. These “plagues” of urchins essentially leave just barren ground behind.
The sea urchins can live for a long time with very little food and effectively eats all new kelp growth and therefore prevents the kelp forest to grow back. This is a cause for concern as the kelp forest creates a vital ecosystem for many other species.