Pelagic red crabs on the shore of Pacific Grove. Photo: ©Kate Cummings

The southern shore of Monterey Bay turned a glistening crimson Thursday morning as thousands of pelagic red crabs swarmed ashore in a rare stranding event attributed to the powerful El Niño in the equatorial Pacific.

"Thousands of tuna crabs on the beach in Pacific Grove this morning – El Niño keeps bringing us interesting things!" naturalist Kate Cummings, who runs Blue Ocean Whale Watch in Moss Landing," stated on Facebook.

Photographer Patrick Webster chronicled the stranding with a series of posts on Instagram, referring to the event as “the other red tide.”

It marks the first time pelagic red crabs, also referred to as tuna crabs because they’re prime forage for tuna, have been documented in Monterey Bay since 1982-83 (another powerful El Niño season), according to the Office of National Marine Sanctuaries. It's only the fifth known time a mass stranding has occurred in the iconic Central California embayment, the first occurring in 1859.

Pelagic red crabs typically roam the currents off Baja California, Mexico, in such abundance that they become prey for several species of tuna, migratory fishes, giant squid and Humboldt squid, sea birds, turtles, whales and pinnipeds.


Pelagic red crabs color the shore red. Photo: Kande Williston/Monterey Bay National Marine Sanctuary

In late spring and early summer, similar strandings occurred in Southern California, primarily in San Diego and Orange counties.

This year's developing El Niño, a warm-water event whose influence reaches far to the north in terms of the increase in sea surface temperatures, could be the strongest ever recorded.

With the warmer water comes a variety of subtropical species, which sometimes can be found along the entire California coast, but predominately in Southern California.

Pelagic red crabs look like baby lobsters, and are considered the most abundant species of microplankton in the California Current.

It's not clear why they strand, but once they do they cannot make it back to the sea and perish, or are consumed by gulls and other seabirds.

Crabs were still coming ashore in the Pacific Grove area on Friday morning and this stranding, like past strandings in Southern California, might eventually require a smelly cleanup effort.

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