While they be fun to look at, a new sight in northern California tide pools are causing quite a bit of concern as the shades of oceanic blue are filled with one-inch blotches of hot pink. The culprits, known as Hopkin's Rose Nudibranch (Okenia rosacea), are sea slugs common to the warmer waters of southern California. But as water temperatures shift, researchers fear that their migration further up the coast may be a sign of what's to come.
Though surveys of tide pools in southern California often find Hopkin's Roses within them, the transects of northern California tide pools are often devoid of the creatures. But as the water temperatures are warming up and down the coast, researchers at universities like the University of California, Santa Cruz are finding the sea slugs in a shocking abundance. In fact, in a series of surveys conducted in the past few weeks in tide pools ranging from Humboldt County to San Luis Obispo, university researchers have reported the highest and northernmost records of the species since the 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" UC Santa Cruz professor emeritus of ecology, John Pearse says. "What makes this event especially exciting for us is that in 2011 we published a paper in which we predicted that oceanographic conditions like we are now experiencing would be marked by heavy recruitment of these and other nudibranchs."
"It's just wonderful to see the prediction coming true."
Some researchers have pointed to global warming as being a potential mitigating factor in the spread of the nudibranchs, but Pearse and his colleagues say that it may be something far more innocuous than that. While the past events occurred during El Niño events, marked by periods of heavy rainfall and warmer-than-average ocean water temperatures, 2015 only shows a 50-60% chance of these conditions according to the National Oceanic and Atmospheric Administration (NOAA).
So then, if it's not climate change and El Niño isn't primarily to blame, then who or what is?
Well according to most intertidal researchers along California's coast, the likely culprit are rare wind patterns that are allowing warm surface waters to remain, boosting the intertidal temperatures high enough for Hopkin's Roses and other species to flourish. But while the sights of the tide pools may be something fun to look at while they last, researchers like Dr. Terry Gosliner of the California Academy of Science caution that the implications of these warmer waters may be far worse the public realizes.
"Our current climate conditions are great for some of my favorite slugs, but we can't ignore that warming seas mean less food for sea birds, and adverse impacts for all marine ecosystems" Gosliner says. "California's unique marine life can't always adapt to so much instability."