Sea urchin population soars 10,000% in five years, devastating US coastline | The Guardian
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.
The underwater annihilation is killing off important fisheries for red abalone and red sea urchins and creating such havoc that scientists in California are partnering with a private business to collect the over-abundant purple urchins and “ranch” them in a controlled environment for sale to a global seafood market.
“We’re in uncharted territory,” said Scott Groth, a shellfish scientist with the Oregon department of fish and wildlife. “You can’t just go out and smash them. There’s too many. I don’t know what we can do.”
The explosion of purple sea urchins is the latest symptom of a Pacific north-west marine ecosystem that’s out of whack.
Kelp has been struggling because of warmer-than-usual waters in the Pacific Ocean. And, in 2013, a mysterious disease began wiping out tens of millions of starfish, including a species called the sunflower sea star that is the only real predator of the ultra-hardy purple urchin. Around the same time, the purple urchins had two excellent breeding years – and with no predators, those gametes grew up and are now eating everything in sight.
“You can imagine all of these small urchins growing up, each one of them looking for food, desperate for food. They’re literally starving out there,” said Steven Rumrill, lead shellfish expert at Oregon’s wildlife agency. “I’ve seen some big-scale fluctuations in the populations of sea stars and urchins, but never on this magnitude.”
