Restoration transformed sea urchin desert into rich forest

A long-term collaboration between NIVA and the Institute of Marine Research has resulted in a new publication documenting the long-term effects of sea urchin removal in Finnmark. The project is one of the world's largest kelp forest restoration initiatives, both in terms of area (equivalent to 100 football pitches), duration, and the many ecosystem benefits that have been documented.

The project started as a response to the extensive grazing of kelp forests caused by sea urchins.

“Using 200 tons of quicklime, approximately 21 million sea urchins were removed in a large-scale operation in 2013. Within a year, the kelp forest returned, and this forest has now persisted for almost ten years,” says NIVA researcher Hartvig Christie.

Millions of plants, billions of small animals

Four different species of kelp, and a number of other plants and animals that belong in the kelp forests, have colonized the previously deserted seabed. Juvenile codfish have also found their way to the new kelp forests.

“The most striking thing was how quickly the dense kelp forests returned, and how quickly the fish found their way to these rich oases,” says Christie.

The surveys showed no effect of liming on the environment apart from on the sea urchins.

The publication describes how the return of kelp forests led to an increase of kelp fauna, that after a couple of years was estimated to 3.5 billion small animals. The authors believe that this number will increase significantly, and that the kelp forest will provide a daily food supply for cod and other fish in the fjord.

Christie estimates that the more than 10 million new kelp plants bind around 2,000 tons of CO₂. A real long-term benefit is that the new kelp forest will add around 7,500 tons of kelp material to the fjord's food chains every year.

“The project shows that it pays to restore kelp forests. With such large benefits as this limited experiment can show, we hope that it will stimulate investment in the restoration of the large areas of sea urchin deserts that still remain,” says Christie.

The importance of management

The study emphasizes the importance of active management to protect and restore marine ecosystems. Although the lime treatment was successful, long-term success depends on controlling sea urchin densities. The king crab, that has become an abundant predator in the area, has played an important role for the maintenance of the restored kelp forest.

“The king crab eats sea urchins and has contributed to the regrowth of kelp forests even outside the lime-treated areas. This shows the importance of predators in keeping new generations of sea urchins at a low level,” explains Christie, who adds that it is best to focus on native predators, rather than alien species such as the king crab.