Modeling and mapping green sea urchins: mutual benefits for commercial harvest and regrowth of kelp forests in Norway

The green sea urchin (Strongylocentrotus droebachiensis) occurs in high densities along the northern coast of Norway and is regarded as a big problem due to its ability of turning high-productive kelp beds (Laminaria hyperborea and Saccharina latissima) into sea urchin-dominated barren grounds of low diversity and productivity. However, the gonad of the sea urchins is also regarded as a delicacy and thus represents a potentially huge resource for industrial and commercial development. We have studied the basis for harvesting green sea urchins commercially by applying GIS models of barren grounds combined with statistical models of density distribution of sea urchins. The statistical models are based on density data from field studies (793 stations covering the coast from 63˚N to 71˚N). We estimated the environmental gains of “overfishing” the sea urchins resulting in a likely recovery of kelp biomass and production. The recovery of kelp biomass includes an additional positive effect through binding of CO2, and recovery of kelp associated biodiversity and resources. We discuss the mutual benefits of commercial harvesting of sea urchins in the boundary areas between un-grazed kelp forest and barren grounds with a sufficient effort to cause regrowth of kelp forests on a total of 3500 km2 of potential habitat along the Norwegian coast.