1/30/15
Roses are blooming in Central and Northern California tide pools, leaving scientists scratching their heads.
Warmer ocean temperatures have triggered a population explosion of the Hopkins' rose nudibranch beyond its normal Southern California range.
The brilliant pink sea slug is uncommon north of San Luis Obispo and even rarer north of San Francisco. However, scientists in Santa Cruz, San Francisco and Bodega Bay have spotted the tiny puffs concentrating in tide pools as far north as Humboldt County.
Unexplainable rare wind patterns in the past year have heated West Coast oceans, luring schools of warm-water species like the nudibranch.
There's been many unusual visitors. In September, a fisherman near San Francisco caught a sea turtle normally found off the coast of Mexico and the Galapagos. Humpback whales and dolphins are lingering in the Monterey Bay.
Ocean temperatures off the coast remained about 5 degrees higher than normal for much of last year.
"It never really cooled off and gradually got warmer and warmer," said Logan Johnson, a forecaster with the National Weather Service in Monterey. "It's still running about 58 degrees right now in the Monterey Bay, and it hasn't cooled off to the lower 50s."
These high temperatures harken El Niño years, but what's causing the uptick in temperature is the absence of a normal process called upwelling.
"Northwesterly winds will basically blow away water at the surface, and deeper, colder waters will rise up and replace it," Johnson said. "We just didn't see those winds."
A team of researchers from UC Santa Cruz's Institute of Marine Sciences, UC Santa Barbara's Marine Science Institute, the California Academy of Sciences and University of Zadar, Croatia, published a 2011 paper that predicated these rare oceanographic conditions would lead to a bloom of the nudibranchs.
"At first, we were worried the nudibranchs were being killed off by something, but it turns out it's more of a natural fluctuation," said John Pearse, ecology and evolutionary biology professor at UC Santa Cruz. "We're now entering again another warm phase. We have no idea whether this is part of the ongoing oscillation back and forth or if it's perturbed by global warming; probably both."
Researchers believe colder currents likely are limiting the southern sea slug's range because their prey lives abundantly along the Pacific Coast up to British Columbia. The Hopkins' rose nudibranch gets its pink pigmentation by eating a rose-colored encrusting bryozoan, a moss-like species.
But now, northward and onshore currents are carrying the slug's larvae to tide pools -- they aren't being washed away by upwelling.
"The nudibranch can just crawl short differences and don't live very long," said Jeff Goddard, a scientist at UC Santa Barbara's Marine Science Institute, so they're useful in monitoring quick changes in ocean conditions.
Northbound southern species is just one effect of warmer water.
"There are some detrimental impacts to the ecosystem," Goddard said. "Higher temperature often means the water is less productive."
Fewer plankton and thinner kelp forests reverberate up the food chain and, for example, affect salmon and sea birds.
