The kelp species Saccharina latissima and Laminaria hyperborea form highly productive dense forests in the sublittoral zone along the Norwegian coast, providing habitat, food, nutrients, and shelter to numerous species. The total kelp forest area along the Norwegian coast line was estimated to be about 7900 km2 in 2011, but this is estimated to be less than 50% of the original coverage, with an estimated 9800km2 of kelp forest lost. The causes of kelp forest loss include climate change, increased runoff of particles, increased nutrients and growth of filamentous algae. However the major cause is overgrazing caused by high densities of sea urchins.