The photos are striking: San Diego's coastline from Ocean Beach to La Jolla covered in red from an invasion of small red tuna crabs, or pelagic red crabs. But why are they flocking to the beaches by the thousands?

According to CNN, Linsey Sala, a museum scientist at the Scripps Institution of Oceanography, UC San Diego, said that the red tuna crabs may have been crawling up San Diego's beaches for the past few weeks due to warm water carrying the crustaceans from their usual home along the west coast of Baja California and the Gulf of California.

"Typically such strandings of these species in large numbers are due to warm water intrusions," Sala said.

Daniel Pondella II, director of the Southern California Marine Institute, told the Pilot in January that the crab phenomenon "could just be a sign of the warm water we're currently experiencing."

Additionally, some speculate that warm ocean currents from the tropical Pacific migrate farther north than usual in a growing El Nino event. 

The crabs are 1 to 3 inches long and do not pose a threat to humans, the Los Angeles Times reports.

"Once they are on the sand their life cycle has typically come to an end," Marine Protection Officer Jeremy Frimond said. "However, some may still move slightly as their death is not instant once beached."

The animals move with ocean currents, and occasionally are carried to the shore.

Some beachgoers in Newport Beach were spotted picking up some live crab and taking them home to cook up and eat, Newport lifeguard battalion Chief Brent Jacobsen said.

"I heard they were pretty salty," Jacobsen said.

However, experts warn against eating the red tuna crabs because they could contain unknown toxins, CNN reports.