Warm ocean temperatures have allowed a non-native bright pink sea slug to arrive in tide pools of central and northern California.
The Hopkins' rose nudibranch (Okenia rosacea), is common in Southern California but is rarely seen in the state's northern regions, the University of California-Santa Cruz reported. Recently, densities of up to dozens per square meter in tide pools from San Luis Obispo to Humboldt Counties have been reported. These are the highest densities of the species and northernmost sightings seen since the extremely strong El Niños of 1983 and 1998.
"We haven't seen anything like it in years. These nudibranchs are mainly southern species, and they have been all but absent for more than a decade," said John Pearse, professor emeritus of ecology and evolutionary biology at UC Santa Cruz.
The unique factor of the recent sightings is that there was no El Niño this year. In a 2011 paper researchers predicted a high recruitment of these brightly colored creatures during periods of warmer temperatures, northward currents, and weak upwelling; all of which are present today.
Since Hopkins' rose nudibranches are fast-growing and have lifespans of less than a year they are ideal specimens for tracking changes in ocean conditions and circulation patterns. The researchers suggested the change in distribution of the sea slugs indicates a major climate shift from cold to warm coastal waters.
"Although the index values of the Pacific Decadal Oscillation have really jumped the past few months, it's probably still too early to say, at least until we become better at decoding the signals," said Jeff Goddard, a project scientist at UCSB's Marine Science Institute. "However, if a decadal shift is in progress, there's a good chance the next El Niño will be a major event, on par with the 1983 and 1998 events, and bring with it myriad surprises from the south."
