Amphipods—small, shrimplike crustaceans in most aquatic ecosystems—start to fall apart once they hit depths of 4500 meters. There, a combination of crushing pressures, low temperature, and higher acidity causes the calcium carbonate in their exoskeletons to dissolve, making them vulnerable to pressure and predators. Now, scientists have discovered how one species, Hirondellea gigas, can survive in the deepest part of the ocean: with aluminum suits of armor.
Researchers first analyzed H. gigas specimens found at the bottom of the Challenger Deep, more than 10,000 meters below the surface of the ocean. They found that this extreme amphipod constructs a personal suit of armor—a layer of aluminum hydroxide gel covering the surface of its exoskeleton. But aluminum isn’t abundant in ocean water, making it hard to source as a building material. It is, however, abundant in ocean sediment.
To figure out how H. gigas accesses its aluminum, the team exposed sediment from the Challenger Deep—which the crustacean likely swallows when eating—to chemicals in its gut. Within that acidic environment, a byproduct of the plants in its typical diet reacts with the metal-rich sediment to free up aluminum ions. When these aluminum ions are released into alkaline seawater, they transform into protective aluminum hydroxide gel, the researchers report this month in PLOS ONE.
The aluminum armor appears to both relieve stress from deep-sea pressures and prevent the amphipod exoskeletons from leaching calcium carbonate and disintegrating. Thanks to these findings, scientists are one step closer to understanding how it is possible to survive in one of the world’s harshest environments.