Twice in my three decades living on the Monterey Peninsula I’ve witnessed two invasions by pelagic red crabs, also called tuna crabs, or langostino by some. These are spectacular and rare occurrences along our coast, although we’ve had a couple this year, the most recent last week. The first local invasion that I could find mention of was in 1895 (Boyd 1967).

 A pelagic red crab (Pleuroncodes planipes) looks like a small lobster — it’s even called a squat lobster — about 5 inches (13 cm) long. They’re part of the “micronecton,” that is, small swimming marine organisms that live in the water column. Adults tend to live closer to the bottom and feed on plankton near the surface. However, they’re swimming abilities are limited and they’re easily caught up in tides and currents. As a result, they sometimes end up in the wrong place (for a pelagic crab), like our Monterey Bay beaches.

This year, as with the last invasion I observed in the early 1980s, was an El Niño year, a natural recurring event (every 7 years or so) when waters off Peru and Ecuador become unusually warm, changing Pacific water flow and weather worldwide. The sight of red crabs indicates warm subtropical waters moving northward off the west coast of the U.S. These crabs are most typically found off Baja California and in the Gulf of California, although they are seen off Chile and up to Washington state.

The brightly colored crabs not only attract the attention of people, but that of shorebirds, especially gulls. They were gorging themselves on the bounty in the shallow water, jumping the waves and trying to avoid one another. The crabs are probably a welcome, easy, tasty meal. Many gulls looked too full to move.

While researching this post, I found a Yummly page with red crab recipes. If gulls, tuna and whales can enjoy them, why not people? Although, the Scripps Institution of Oceanography recommends not eating red crabs because of possible toxins (of which significant amounts were found in shellfish this year causing a long delay to the opening of the Dungeness crab season). If not edible, the display is certainly a shoreline spectacle.

References & Sources

Boyd, C.M. (1987). The Benthic and Pelagic Habitats of the Red Crab, Pleuroncodes planipes. Pacific Science XXI (3): 394-403.

National Marine Sanctuaries. Pelagic Red Crabs. 

Scripps Institution of Oceanography UCSD. Red Crabs Invade San Diego Shores.