350 Million Sea Urchins Found On One Oregon Reef; 90% Of N. California Giant Kelp Forests Gone

Tens of millions of voracious purple sea urchins that have already chomped their way through towering underwater kelp forests in California are spreading north to Oregon, sending the delicate marine ecosystem off the shore into such disarray that other critical species are starving to death.

A recent count found 350m purple sea urchins on one Oregon reef alone – more than a 10,000% increase since 2014. And in northern California, 90% of the giant bull kelp forests have been devoured by the urchins, perhaps never to return. Vast “urchin barrens” – stretches of denuded seafloor dotted with nothing but hundreds of the spiny orbs – have spread to coastal Oregon, where kelp forests were once so thick it was impossible to navigate some areas by boat.

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The devastation is also economic: until now, red abalone and red sea urchins, a larger and meatier species of urchin, supported a thriving commercial fishery in both states. But 96% of red abalone have disappeared from California’s northern coast as the number of purple sea urchins increased sixfold, according to a study released this week by the University of California, Davis. Last year, California closed its red abalone fishery, which poured an estimated $44m into the coastal economy per year, and Oregon suspended permits for its 300 abalone divers for three years. The commercial harvest of red sea urchins in California and Oregon also has taken an enormous hit.

“That’s a huge economic loss for our small coastal communities,” said Cynthia Catton, a research associate with the UC Davis Bodega Marine Lab. “In California, there were 30,000 to 40,000 participants in [the abalone] fishery every year for decades, and for the first time ever that fishery had to close.” And while the purple urchins have eaten themselves into starvation as well, unlike other kelp-dependent creatures, the species can go into a dormant state, stop reproducing and live for years with no food. That means the only way to restore the kelp is to remove or destroy the purple urchins. Scientists estimate that in Oregon alone, it would take 15 to 20 years to remove all 100m lb (45m kg) of purple urchins recently surveyed on just one large reef.

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https://www.theguardian.com/environment/2019/oct/24/sea-urchins-california-oregon-population