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SOURCE: San Francisco Chronicle

DATE: October 22, 2019

SNIP: A climate-related catastrophe off the California coast has resulted in the death of 90% of the kelp from San Francisco to Oregon as an explosion of ravenous urchins devours everything in sight. And it’s happening at the same time native fish in San Francisco Bay are dying out, two studies released Monday documented.

The studies, by government, university and scientific institute researchers, offer a disturbing look at an underwater ecosystem suffering more than anyone previously suspected — along the coast, in San Francisco Bay and in the Sacramento-San Joaquin River Delta.

“It’s very serious,” said Laura Rogers-Bennett, a Fish and Wildlife senior environmental scientist and a research associate with UC Davis’ Bodega Marine Laboratory who was lead author of the kelp study. “This is a huge environmental disaster underwater.”

The kelp study, published Monday in the journal Scientific Reports, chronicles a dramatic decline in the ocean ecosystem that started in 2013 when millions of sea stars along the coast of California withered and died. Without their main predator, the native kelp-eating purple sea urchin population skyrocketed to 60 times its historic numbers.

That was followed, from 2014 to 2017, by a marine heat wave and an El Niño weather event of unprecedented scale. The ocean heated as much as 6 degrees during that time, and toxic algae formed along the coast, killing many species.

The warm water began killing off the lush forests of bull kelp, and then ravenous urchins finished them off, leaving a barren seascape.

Only about 10% of the historic kelp population in a 217-mile-long swath along the entire North Coast of California into Oregon still exists, Rogers-Bennett said, and the problem is spreading. About 50% of the kelp south of San Francisco, including Monterey Bay, is also gone.

That, in turn, has caused the mass starvation of red abalone and other species dependent on kelp from Baja California to Alaska. The red abalone fishery was closed in 2018 because of the die-off.

“What we’re seeing now are millions and millions of purple sea urchins, and they’re eating absolutely everything,” Rogers-Bennett said. “They can eat through all the anemones, the sponge, all the kelp, the fleshy red algae. They’re even eating through calcified alga and sand.”

Bull kelp is a key indicator of ecosystem health because it is one of the fastest-growing plants on Earth, capable of growing 2 feet a day, Rogers-Bennett said. It thrives in cooler water temperatures, but the vast kelp forests that once existed failed to return even after the warm water period earlier in the decade ended.

The problem, she said, is that bull kelp is an annual plant — meaning it must regrow from seeds every spring and summer — and the ravenous purple sea urchins are eating even the spores, or seeds, that the kelp need to regenerate.

Things aren’t any better inland, where a new State of the Estuary Report released Monday documented the steady decline since the 1980s of virtually every native species of fish in San Francisco Bay.

The fish most at risk are chinook and coho salmon and delta smelt, which have suffered from loss of habitat, lack of cold water, polluted runoff, elimination of flood plain habitat and construction of dams that have cut off spawning grounds.

In the Sacramento-San Joaquin River Delta, 96.8% of the more than 380,000 acres of vegetated wetlands that once existed is gone. Only about 15% of the historic marshland habitat around the main part of San Francisco Bay still exists, according to the study.