The collapse of Northern California kelp forests will be hard to reverse

Satellite imagery shows that the area covered by kelp forests off the coast of Northern California has dropped by more than 95 percent, with just a few small, isolated patches of bull kelp remaining. Species-rich kelp forests have been replaced by 'urchin barrens,' where purple sea urchins cover a seafloor devoid of kelp and other algae. A new study documents this dramatic shift in the coastal ecosystem and analyzes the events that caused it.