Red Crab Swarm Is A Scientific Enigma — Creatures Gather In Massive Crustacean Traffic Jam

Nature is infinitely mysterious and scientists often find themselves surprised and perplexed by new and unexpected discoveries.

That’s what happened to a team of scientists studying an underwater mountain near Panama. They were in a submersible vessel, looking for something else, when they came upon a swarm of red crabs, Live Science reported.

Biological oceanographer Jesus Pineda, who works at the Woods Hole Oceanographic Institution, described that unusual day.

“When we dove down in the submarine, we noticed the water became murkier as we got closer to the bottom. There was this turbid layer, and you couldn’t see a thing beyond it. We just saw this cloud but had no idea what was causing it. We saw a cloud, a really big cloud. We were thinking, what in the world is this?”

It was a swarm of red crabs, thousands of them, scurrying along the seafloor and kicking up a plume of mud 30 feet high, The Los Angeles Times described.

Scientists were shocked by the swarm because they’d never seen anything like it before. They were even more shocked when they found out the little crustaceans were the culprit, because they’re not supposed to be so far south.

When Pineda and his colleagues saw the swarm they were at a depth of 1,200 feet. They counted three groups, tightly clustered together; the densest grouping was at the center, with about 78 of the creatures counted per square meter, or seven per square foot.

Red crabs are reddish orange and look like mini-lobsters. Their usual haunt is off the northwest coast of Mexico, but they’ve been seen off southern and central California during El Niño. Also called squat lobster and tuna crab (yellowfin tuna like to eat them), they swim and drift in the water when they’re young, which means they are vulnerable to changes in ocean currents as caused by El Niño.

The swarm was found at an underwater mountain off the coast of Panama called the Hannibal Bank seamount. The spot is of interest to scientists because it attracts diverse populations of marine life, and scientists do not yet know why. The red crabs only add to the mystery.

So far, researchers believe that seamounts redirect ocean currents and nutrients near the water’s surface, which also gets more light. Phytoplankton and plants can grow there, and then large fish and other animals follow.

But why the red crabs? They’re not supposed to be near Panama at all and have never been spotted in that area. Adding to the enigma is two other swarm sightings. A huge number were found stranded on a San Diego beach in 2015. Later that summer, they were seen in the Channel Islands off the coast of southern California, The Christian Science Monitor added.

The swarm of red crabs near Panama is likely unrelated to these other sightings, but their presence alone raises questions and hints that the species’ range is more far-reaching than once believed.

Red crab swarm spotted further south than ever
An underwater mountain. [Photo By Jung Hsuan/Shutterstock]
“To find a species at the extreme of their range, and to be so abundant, is very unusual,” Pineda noted.

He does have a theory, however: the red crabs, which usually hang out in shallow waters, may have plunged into the ocean’s depths to flee from predators.

Even more significant is the fact that a swarm like this has never been seen before, in red crabs or any other sea creature. Pineda searched and searched for evidence of other swarms in lobsters, shrimp, and other species, but found nothing. He believes the swarm could just be the settling of a huge “school.”

“In other regions, (they) migrate daily. During the day, they are found at depth, whereas at night, they swim up, and can be found near the surface of the ocean. My hypothesis is that the swarms represent a ‘school’ … that settled down.”

The surprised and confused scientists will head back to the seamount to piece together the puzzle.

[Photo By vanchai/Shutterstock]

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