A sea urchin explosion threatens a delicate kelp forest ecosystem.
WHEN CORONAVIRUS SHUTDOWNS SCUTTLED international travel for underwater photographer Brandon Cole, he sought “aqua therapy” in what had once been familiar home turf: the giant kelp forests off the California coast. But what he found was stark and shocking. An explosion of purple sea urchins moved like a voracious “advancing army,” devouring once-lush stands of giant kelp in central California’s Monterey Bay (above). Urchins chomp the tangled holdfasts that anchor the kelp to rock and also eat kelp’s ropelike stalks and leafy blades. Farther north, along the coasts of Mendocino and Sonoma counties, Cole saw total devastation of kelp forests. “It was like an atomic wasteland,” he says.
The urchin explosion began in 2013 as a wasting disease began killing sea stars such as the giant sunflower sea star, the main predator of urchins. Warming seas have also weakened kelp, speeding its decline. The loss of kelp—a vital food for abalone—has devastated the once-thriving abalone fishery (now closed) and hurt the snails, fish, crabs and other animals that feed on or hide in kelp. “I fear this enchantingly beautiful ecosystem is becoming a ghost town,” says Cole.
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Bird’s-eye view of a forest of giant kelp
This aerial view shows California’s Carmel Bay, near Point Lobos State Natural Reserve. The rocky reefs, kelp forests and dramatic granite pinnacles in these protected waters are home to abundant fish and invertebrate species—and offer some of the finest scuba diving in California.
Under the kelp canopy
Blue rockfish swim underneath a healthy forest canopy of giant kelp plants in the North Monastery region of Carmel Bay, just south of Monterey Bay off the coast of California. Kelp forests farther north have been largely denuded by grazing sea urchins. Underwater photographer Brandon Cole, ”My sincere hope is that the tide turns soon to spare the Monterey Peninsula kelp the same widespread devastation experienced farther up the California coast.”
Bull kelp
A blue rockfish swims past the air-filled bladders of bull kelp of the California coast. These air-filled bladders, called pneumatocysts, buoy up the stalks and blades of this fast-growing marine algae.
Red abalone surrounded by purple sea urchins
Red abalone—a highly prized sea snail—and sea urchins eat kelp and algae. In recent years, urchin numbers have soared, and the spiny invertebrates have devoured kelp and algae, causing abalone numbers to plummet.
Giant sunflower sea star
This giant sunflower sea star clings to a colorful rocky reef on the Monterey Peninsula in the early 2000s. Once abundant, this species has been especially hard hit by a sea-star wasting disease. Detected in 2013, the disease caused population losses of more than 90 percent in some areas. Sea stars are the main predator of sea urchins, so the loss of this key species from kelp forests in northern and central California has contributed to the explosion of the spiny invertebrates.
Survey of marine life in a kelp forest in Monterey Bay
Reef Check California’s Maxwell Seale conducts a survey of marine life in a kelp forest on a rocky reef in Monterey Bay. Here, purple sea urchins are feeding on bull kelp, clustered together on the holdfasts, the plant’s base, which anchors kelp to rocks. When urchins wipe out kelp and other algae, they leave behind a denuded substrate called “urchin barrens.” Many kelp forests in central and northern California have been decimated, significantly altering the ecosystem.
Lover's Cove in Monterey Bay
Once home to a thick kelp forest that harbored a diverse population of fish and invertebrates, Lover’s Cove is now an urchin barren. Yet as sea urchins raze giant kelp and bottom algae and create a bleak scene of rock and sand, they too suffer nutritionally. Some urchins die, leaving behind white skeletons called “tests.” Most enter a near-dormant state where they can survive without eating for years.
Dead sea star with wasting disease
This dead sea star, likely a Stimpson’s sun star, has died from wasting disease. This disease has affected more than 20 species of sea stars in the northeast Pacific Ocean, causing significant mortality and impacting entire ecosystems. The exact causes of the disease are still not entirely understood, though a virus appears to be at least partially responsible. The affliction causes lesions to develop and spread through the animal’s body.
Purple sea urchin with wasting disease
Afflicted with wasting disease, the spines of this purple sea urchin are falling off. When urchin populations explode in the absence of abundant predators such as sea stars, they raze kelp and algae, creating urchin barrens where there is little left to consume. The wasting disease is likely tied to stressors that include high urchin densities, poor nutrition, warming waters and poor water quality.
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