Community activists save the sea.

• Author: Helvarg, David
• Position: CORALations

I'M DIVING THROUGH A MARINE reserve off Catalina Island in Southern California twenty-two miles from Los Angeles. There's a rock wall with lots of spiny urchins, where I spot four lobsters in caves and a big purple sea hare, and a couple of five-foot bat rays flying through the water column that is also teaming with kelpfish, senoritas, red and black California sheephead, and orange garibaldis, like goldfish on steroids.

My dive buddy Scott and I move into the kelp forest with its tangled brown strands, some fifteen feet thick and rising fifty feet to the surface, infused with afternoon cathedral light like an underwater redwood grove. I check out the bottom cover, where pink strawberry anemones appear as tiny flowers next to a decorator crab, covered in red seaweed and green algae. Just then a 600-pound sea lion streaks past like some sleek, flexible torpedo on the hunt. Distracted, I don't watch where I'm going and soon have to untangle my tank and flotation device from the clutches of several rubber-hose-like kelp strands.

Giant kelp, along with bull kelp, are the dominant marine plant species along this coast and can grow a foot a day, which sounds awesome till they're yanking on your regulator hose. While I'm clearing my gear, Scott spots an old abandoned hoop net used for catching lobsters before this patch of ocean was protected and frees a four-foot leopard shark trapped inside. Back topside, a pod of Risso's dolphins, some twelve-feet long, cruises by feeding on squid.

Last year, California set aside 16 percent of its state waters as marine reserves like this one after a fierce thirteen-year battle pitting the recreational fishing industry against conservationists, scientists, sport divers, and others. Much of the conflict resulted from a top-down process. The Department of Fish and Game put out maps showing the locations of the reserves without local consultations. As the backlash grew, the state had to scrap its original plans and start over by holding public hearings up and down the coast. Luckily, because almost every Californian has a sense of entitlement to the ocean, this unnecessarily rowdy process led to a reasonable outcome. Today, California's world-class state park system has moved into the water column.

In the 1990s, scientists began suggesting 20 percent of the ocean be set aside as Marine Protected Areas, extraction-free zones that could act as reserves for the threatened biodiversity of the seas, what National...