In 2013, California began removing millions of purple urchins from barren reefs; seven years later, more than 55 acres of kelp forest had returned

• Kelp forests are among the most productive ecosystems in the ocean.
• They provide habitat for fish and invertebrates while supporting marine mammals and other wildlife.
• [Photo credit: Enric Sala, National Geographic]Beneath the waves off Southern California, a once-lush underwater forest had been reduced to something resembling a desert.