Crustaceans Fake Out Predators With Glare-Resistant Coating

Today in "You Guys, The Ocean Is So Weird": Scientists say some crustaceans wear mattifying living layers to hide from predators. A report on the sea critters’ clever camo was published in the journal Current Biology.

Amphipods are a group of shrimplike crustaceans that make their homes in a variety of venues, from freshwater to beaches and deep into the sea. They’re not particularly charismatic creatures, but charisma doesn’t count for much in the darkness of the ocean. What counts is adaptability.

Some species have developed glowing fishing poles; others, sparkling arms. Some creatures light up in order to be seen, while others use illumination to hide. Others, like these amphipods, would prefer to avoid light altogether.

This is harder for them than it would be for you or me. Why? Because they’re naturally transparent—and reflective.

Scientists put seven specimens of mid-water amphipod species under high-powered microscopes and looked closely at their shells. When they zoomed way in, they discovered that all the amphipods were sporting little coats of what looked like beads on their bodies and legs. The beads themselves are microscopic, ranging from 50 to 300 nanometers in diameter depending on the species. This makes them just the right size and shape for absorbing undersea light.

Coating on the leg of a Cystisoma amphipod. Image Credit: Laura Bagge, Duke University

 
Biologist Laura Bagge is lead author on the study and a Ph.D. candidate at Duke University. Speaking in a press statement, she said the coating reduces reflections “the same way putting a shag carpet on the walls of a recording studio would soften echoes.” Some species’ coatings could cut down on glare by as much as 250-fold, rendering them effectively invisible to wide-eyed predators.

The coats are certainly effective. But what are they?

We're not totally sure. “They have all the features of bacteria,” Bagge said, “but to be 100 percent sure, we’re going to have to perform an in-depth sequencing project.”

Crustaceans shed their shells on a regular basis. For carefully camouflaged amphipods, this could mean becoming shiny again—unless they take their special coats with them. If the mattifying layers are indeed made of bacteria, they could easily be transferred to a new shell as the amphipod tugs its way out of the old one.

Mama Phronima with offspring inside a salp nest. Image Credit: Laura Bagge, Duke University

 
They could also share them with their kids. Phronima amphipods raise their babies in the hollowed-out bodies of a translucent creature called a salp. The researchers say it would be pretty simple for a mama amphipod to pass her coating materials on to little ones in the nest.
 
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