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Crabs Swarm on the Seafloor When (from left) WHOI biologist Jesús Pineda, pilot Eli Temime, and WHOI researcher Victoria Starczak descended on Hannibal Seamount in the submersible Nadir, they were astonished to see a huge swarming throng of crabs on the seafloor. (Hanu Singh, Yogeh Girdhar, Jeff Anderson, WHOI)

Crabs Swarm on the Seafloor

Life turns up in curious places in the ocean

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Expeditions to the tropics and Antarctica have turned up crab populations—for better or worse—in unexpected parts of the globe.

At the Hannibal Bank Seamount, an 1,180-foot-high undersea mountain off Panana’s Pacific, a 2015 expedition led by Woods Hole Oceanographic Institution (WHOI) marine ecologist Jesús Pineda found mesmerizing swarms of red crabs on the seafloor—where the water has almost no oxygen. To investigate the Pleuroncodes planipes crab swarms, the research team used cameras mounted on an autonomous underwater vehicle called SeaBED, developed by WHOI engineer Hanumant Singh. DNA analyses of the Hannibal crabs revealed that they were the same species as crabs living off Baja California, where tuna and other big fish thrive. Hannibal Seamount is also an ecological “hot spot” where diverse marine life flourishes, and Pineda believes the crabs could be an important source of food that helps explain Hannibal’s abundant fish populations.

More than 5,000 miles away, another Singh-developed camera captured images of a different crab species—this one with potentially dire ecological impacts. Using the robotic Seasled camera, a team led by Florida Institute of Technology marine biologist Richard Aronson took the first photographs of breeding populations of king crabs on the continental slope west of the Antarctic Peninsula.

So far, cold water temperatures have kept the crabs from spreading onto the continental shelf, closer to shore. But climate change and warming ocean waters around Antarctica could allow these predatory crustaceans to expand their range. That could spell bad news for current shelf inhabitants, such as sea stars and other spiny-skinned echinoderms. “Because other creatures on the continental shelf have evolved without shell-crushing predators, if the crabs moved in, they could radically restructure the ecosystem,” Aronson said. 

The Antarctic king crab study was funded by the National Science Foundation, the Swedish Polar Research Secretariat, and the Swedish Research Council, and included scientists from Florida Tech, the University of Alabama at Birmingham, WHOI, the University of Gothenburg in Sweden, and the University of Southampton in the U.K. Support for the Hannibal Bank crab study was provided by the Dalio Explore Fund. Research findings were published March 2016 in PeerJ by Jesús Pineda, Victoria Starczak, Annette F. Govindarajan, Yogesh Girdhar, Rusty C Holleman, James Churchill, Hanumant Singh, and David K. Ralston (WHOI); Walter Cho (Point Loma Nazarene University), and Héctor M. Guzman (Smithsonian Tropical Research Institute).

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