Sea urchins are the best studied echinoderms in Icelandic water and a few species are known. The most common in shallow waters, including in Eyjafjörður are the red sea urchin (Echinus esculentus) and the more common green sea urchin (Strongylocentrotus droebachiensis).

The green sea urchin is common along the kelp front in shallow waters but can also be found at several hundred meter depth. He is among a rather few species that has such a vide depth range.

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 it can behave like a locust plague if it is in great numbers. Then the behaviour changes and it starts climbing up the kelp stipes and eating the kelp alive.

This has happened in Eyjafjörður. There the green sea urchin is very common along the kelp front where it is eating the kelp so that the kelp front is retreating and the kelp forests getting thinner. It essentially leaves 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. Therefore the kelp forest does not grow back until the sea urchins area all dead.

In Garðvík, close to the middle of the fjord regular samples have been conducted on this although this is happening all over the fjord. This is a cause for concern as the kelp forest creates vital ecosystem for many other species. Cod and saithe juveniles for example use the kelp forest to hide from predators and forage for food. If the kelp forests disappear their mortalities will probably increase.

Sea urchin have been fished around Iceland since 1992 and reached a zenith in 1994 with 1500 t harvested. The greatest quantities were harvested in Breiðarfjörður and Húnaflói bays, but considerable quantities also in Eyjafjörður. The market for sea urchin roe collapsed in 1997 and catches have been low since that time. There is no lack of sea urchins now and the markets have recovered, but sea urchin roe is a very delicate products and difficult to handle. This is the main reason that the fisheries are currently low.

Green sea urchins grazing down kelp forest in Eyjafjörður (photo Erlendur Bogason) Green sea urchins grazing down kelp forest in Eyjafjörður (photo Erlendur Bogason)

A soliday red sea urchin on a hydrothermal chimney (photo Erlendur Bogason) A soliday red sea urchin on a hydrothermal chimney (photo Erlendur Bogason)