Red crabs have washed ashore Southern California beaches, from San Diego to Newport Beach, possibly due to warmer temperatures. (Scripps Institution of Oceanography, UC San Diego)

Red crabs, by the thousands, have invaded Southern California beaches, washing ashore from San Diego to Newport Beach.

Sea surface temperatures some 4-7 degrees warmer than normal, possibly connected to a radical change in a Pacific ocean weather pattern, are likely driving the crabs northward away from their typical habitat.

[Why these bright, tiny crabs are blanketing Southern California beaches]

“Experts said the crabs … haven’t been seen in the area for decades,” reported the Orange County Register.


La Jolla, California, June 11, 2015. (Scripps Institution of Oceanography, UC San Diego)

The crabs, resembling miniature lobsters too small to eat, are known as tuna crabs or pelagic red crabs.

“Typically such strandings of these species in large numbers are due to warm water intrusions,” said Linsey Sala of Scripps Institution of Oceanography, UC San Diego.

The crustaceans usually inhabit the west coast of Baja California, the Gulf of California, and the California Current (spanning from offshore the U.S. West coast down to southern Baja California), a Scripps news release said.


(Scripps Institution of Oceanography, UC San Diego)

 

In addition to the crabs, the warm Pacific coastal waters have drawn northward a number of other creatures seldom or never previously seen, which last fall included: a live ocean sunfish and warm-water blue shark in the Gulf of Alaska, mahi mahi off the coast of Oregon, a Pacific sea turtle common in the Galapagos near San Francisco, and marlin in the waters off Southern California.

[In the red: West Coast waters are warmest in decades]

“In recent weeks, blue, jellyfish-like creatures known as ‘by-the-wind sailors’ have been spotted, and tropical fish like yellowtail and bluefin tuna are showing up earlier than normal this year,” the Orange County Register said.

The warm plume of water developed in the spring of 2014.


Sea surface temperature difference from normal June 15, 2015 (NOAA)

Nick Bond, a climatologist at the University of Washington, dubbed it “the blob” and published a study exploring its origins. “[The study] finds that it relates to a persistent high-pressure ridge that caused a calmer ocean during the past two winters, so less heat was lost to cold air above,” explained a University of Washington news release. “The warmer temperatures we see now aren’t due to more heating, but less winter cooling.”

The blob has been linked to the weather pattern that has led to drought in California, and much colder than normal conditions during winter in the eastern U.S. the past two years.

The emergence of the blob may be related to a long-term shift in the phase of the Pacific Decadal Oscillation (PDO), from its cool (negative) to warm (positive) phase.


Time series of the Pacific Decadal Oscillation (NOAA)

In a piece earlier this spring, the Post’s Chris Mooney explained how a shift to a positive PDO pattern may spur increasing global warmth:

If the PDO is not only positive but is going to stay that way, it could be a big deal. Here’s why: Some scientists think a persistent cool phase of the PDO cycle may be a key part of the reason why there has been a much discussed “slowdown” of global surface warming recently. And if they’re right about that, then with the end of the cool phase, we may also see an end to any global warming “hiatus.”

[The Pacific Ocean may have entered a new warm phase — and the consequences could be dramatic]

The PDO has been in its positive phase since July 2014, almost a full year. Many of the warmest months on record for the planet have occurred during that span.

[Earth has warmest 12-month stretch on record for fourth straight month]

The flip to the positive PDO, toasty coastal waters and continued global warming could well mean what were previously unusual creature sightings on the West Coast become the “new normal” for years to come.