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Biology

Under pressure: Amphipod uses aluminum to survive in the deep sea

Originally Posted May 2019

Crushing pressures and freezing temperatures prevent many animals from surviving in the deepest depths of our oceans; yet, somehow, a deep-sea amphipod beats all odds and is able to survive and flourish where few other animals can. Scientists have revealed how these amphipods survive under so much pressure.

Source: Kobayashi, H., Shimoshige, H., Nakajima, Y., Arai, W., & Takami, H. (2019). An aluminum shield enables the amphipod Hirondellea gigas to inhabit deep-sea environments. PLoS ONE, 14(4), 0–5. 

 

Think about the harshest and most inaccessible point on this planet and you may jump to thoughts of Mount Everest, a mountain summit so inhospitable we view climbing to the top as an embodiment of human strength and perseverance.  But there is a place on earth so extreme, it has only been visited by humans three times: The Mariana Trench.

The Mariana Trench system is located in the Pacific Ocean. At its deepest point, Challenger Deep, the trenches reach 10,944 m. Image from wikimedia commons

The Mariana Trench is a series of troughs in the Pacific Ocean and is home to the deepest point in the ocean, Challenger Deep, nearly 11,000 meters (over 36,000 feet) below the surface of the ocean. Challenger Deep is so deep, in fact, that even if Mount Everest were placed on the bottom of the trench, the summit would still be over 1 mile below the surface!  Humans would be crushed under the extreme pressures at these depths (more than 1,000 times greater than atmospheric pressures at sea level) and must rely on specialized submarines and submersibles to explore the Mariana Trench.

In addition to this crushing pressure, the Mariana Trench is shrouded in darkness (sunlight cannot penetrate below 1,000m), has near-freezing water temperatures, and receives only trace amounts of food formed in the productive surface waters thousands of meters above. These environmental conditions are so extreme that scientists thought it would be impossible for animals to inhabit the unforgiving waters of the hadal ( below 6000 m deep) Mariana Trench.  Scientists were shocked to realize that life prevails even under the most inhospitable condition.

In an effort to examine the different creatures inhabiting these astounding depths, scientists sent baited traps down to the bottom of the Mariana Trench. When the traps were pulled up to the surface, only a single type of animal was in them: shrimp-like crustacean called an amphipod  (Hirondellea gigas). Scientists were curious to learn how these deep-sea “bugs” could live in the extreme environment of the hadal trenches and how they managed to build their tough outer shells (called an exoskeleton) under such high pressures (Watch how scientists collected the Hirodenellea gigas amphipods).

 

High pressures in the deep sea hinder normal exoskeleton development

The deep-sea amphipod, Hirondellea gigas, is found in the deepest oceanic trenches. Image from wikimedia commons

Calcium carbonate is a critical component used by crustaceans to build their exoskeletons. In shallow water systems, crustaceans absorb this readily-available building block from ocean waters and turn it into a solid, supporting structure in their shells. But as you travel deeper in the ocean, increasing pressures and decreasing temperatures make it harder to turn calcium carbonate into a solid state. At the depths these amphipods reside, calcium carbonate can no longer be solidified and only exists dissolved in the ocean water. So how could the amphipods from the Mariana Trench build an exoskeleton?

When the team of scientists examined the chemical composition of the amphipod’s exoskeleton, they discovered that these amphipods still used calcium carbonate to build their shells, but the scientists also found traces of a mineral never-before seen in crustacean exoskeletons: These deep-sea amphipods use aluminum to strengthen their body armor.

 

Aluminum amphipod armor

Aluminum is abundant in the sediments of the Mariana Trench, and scientists wondered if the aluminum they detected in the exoskeleton was simply a by-product of chronic exposure to the metal. If this were the case, aluminum would be found throughout many body tissues. But scientists only found aluminum in the outer layer of the exoskeleton, ; suggesting it was instrumental in allowing the amphipod to survive and produce its exoskeleton under such great pressures.

A closer examination revealed that the aluminum was only on the outer surface of the exoskeleton, creating a barrier between the hardened calcium carbonate and the surrounding ocean water. The scientists hypothesize that the aluminum protects the solidified calcium carbonate in the exoskeleton from dissolving into the surrounding waters. The scientists suspect that the amphipods are able to ingest aluminum from the sediments and turn it into a different form they can use to coat the outside of their exoskeleton.

The creatures living on our planet have evolved incredible mechanisms to cope with life in even the most extreme environments. We are still learning about the incredible organism inhabiting the farthest reaches of our planet.  As we learn and discover more about the variety of organism in our world, we are able to adapt what we learn from nature in an effort to solve our own problems.

 

Ashley Marranzino

I received my Master’s degree from the University of Rhode Island where I studied the sensory biology of deep-sea fishes. I am fascinated by the amazing animals living in our oceans and love exploring their habitats in any way I can, whether it is by SCUBA diving in coral reefs or using a Remotely Operated Vehicle to see the deepest parts of our oceans.

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