Forests of giant kelp are found all around the world, but only along our coast anywhere north of the equator. In a healthy kelp forest, sea urchins stay in cracks and crevices on the rocky reef to protect themselves from predators. They eat kelp that falls to the ocean floor. In an unhealthy kelp forest, sea urchins feed on living kelp plants that are still intact.
The Science Center's Role
Working in collaboration with Santa Monica Baykeeper, California Science Center divers have removed over 120,000 sea urchins from the reef below the site of the old Marineland of the Pacific on the Palos Verdes Peninsula. This number doesn't include the urchins Baykeeper has removed. This removal will help to give kelp and other algae a foothold on the reef, restoring the kelp forest once found there.
Why is it necessary?
When storms or other disturbances reduce the amount of drift kelp for the urchins, they will emerge from their holes and feed directly on living kelp plants. Predators, in a healthy system, can reduce the urchins and give the kelp a chance to re-grow. Where predators have been reduced (often through human overfishing) and when disturbances reduce the kelp food supply, urchins emerge from their holes and the predators can't keep the numbers down. The urchins reproduce and the population explodes.
With so many urchins, the rocky reef is grazed bare of all but the most resistant algae, leaving almost nothing but bare rock. This is called an urchin barren. Sometimes these urchin barrens can last for years.
Humans are able to restore the balance by reducing the density of urchins to give kelp and other algae a chance to grow back. When this happens, hundreds of species that associate with kelp return to the reef, restoring the previous species diversity.