A recent study by the Oregon Department of Fish and Wildlife (ODFW) found a 10,000 percent increase in purple sea urchins over the past five years. The spike threatens the Oregon coast kelp beds and diversity.
ODFW’s Scott Groth, a shellfish scientist led the study. He said it’s a complex issue, but he thinks the rise in ocean temperatures and the demise of sea stars are partly to blame.
“There’s kind of this perfect storm situation where everything has been going in this purple sea urchins way and the result is this gigantic increase,” Groth said.
Sea stars, namely pycnopodias or sunflower sea stars, prey on urchins. In 2014, sunflower star populations were decimated by wasting disease. Their decline means urchins can thrive largely unchecked.
Groth’s study recorded 350 million purple sea urchins living near Port Orford, Oregon since 2014.
“It went from an area where there basically wasn’t purple sea urchins, to an area where now purple sea urchins dominate,” he said.
Urchins will often overgraze kelp beds and form an Urchin Barren, where diversity in the area drops to only urchins and rock.
“[Purple sea urchins] tend to compete with abalones and the commercially valuable red sea urchins, but they also just eat anything,” Groth said.
Further north in Newport, Oregon Coast Aquarium Director of Husbandry and offshore dive research team leader Jim Burke, said he’s seen similar changes.
“Now there are thousands and thousands, anywhere from smaller than a golf ball to baseball-sized urchins,” Burke said.
With the sheer numbers of purple sea urchins on the coast, researchers are left looking for feasible solutions.
Burke said he’s hoping sunflower sea stars will make a rebound, though he acknowledged that he hasn’t seen one in Oregon during his dives.
Another major predator for urchins is sea otters. Burke said they could potentially come down from Washington.
“The caveat of that though is that sea otters also depend on kelp to raft up in and seek refuge,” Burke added.
Purple sea urchins are only appealing to predators, including humans, when they eat kelp said Scott Groth with ODFW. On the possibility of harvesting them for human consumption like Uni, Groth said Uni comes from red sea urchins, which are larger and meatier.
“With these sea urchins that are a problem, they don’t have any market value, they’re just like little sea urchin zombies out there, not much inside of them,” Groth said.
He added, even if purple sea urchins could be marketed, whether through harvesting or by other means, there’s too many of them to make a dent.
Both Burke and Groth agreed that another solution may be to accept a different environment.
“These sea urchins live a hundred years, in some cases, and the kelp is an annual plant and it might just be the perfect storm that this happens once in a while,” said Groth.