Baja California ain't a bad life for the pelagic tuna crab, or Pleuroncodes planipes. But the squat, little lobster-like creatures are making Southern California beaches more crowded than the Golden State Warriors bandwagon. And by the looks of Instagram and Twitter, you've observed them:
Strandings observed over time
Tuna crab strandings have been observed for 60 years. “Typically such strandings of these species in large numbers are due to warm water intrusions," says Linsey Sala, collection manager for Scripps' Pelagic Invertebrates Collection.
Beach sightings only partly capture whats going on out in the open ocean.
"Red crabs are abundant in the water column where we are ca. 10 nm west of Pt. Loma, but they are very patchy," wrote Scripps biological oceanographer Dr. Mark Ohman in an email to me from the research vessel Sproul, now cruising through the California Current System. "At one point we traveled through a patch I estimated at 100,000-400,000 individuals visible near the sea surface, but immediately afterward almost none were visible for a few miles."
Red crabs migrate up and down in the water column every day, Ohman says, making them vulnerable to changes in currents that transport water northward.
But they're probably not a sign of climate change yet.
"If they were to persist for many years, that would signal a change in ocean conditions," Ohman says.
El Niño & "The Blob"
The red crabs may signal an El Niño event, still predicted for this fall. "It is quite possible that the local presence of red crabs is an expression of ocean circulation change associated with that event," Ohman says.
One complication is that northward moving water happens in association with El Niño, and without it.
They may also be influenced by a warm patch of water that stretches from Southern California north to the Bering Sea. Nicknamed "The Blob," the huge area of water was first spotted in 2013. More blobs started showing up last near, on average at least 5 degrees warmer than usual.
Earlier this spring, researchers at NOAA and the University of Washington released a study concluding that warmer ocean temperatures "aren’t due to more heating, but less winter cooling." The blob doesn't appear to be caused by climate change; instead, it's a by-product of recent trends in surface ocean temperature and variability in the Pacific.
“This is a taste of what the ocean will be like in future decades,” said Nick Bond, a climate scientist at the University of Washington. “It wasn’t caused by global warming, but it’s producing conditions that we think are going to be more common with global warming.”
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