Camouflaged Predators of the Deep: Ultra-Black Eels' Evolutionary Strategy Revealed

Researchers have determined that ultra-black eels in the deep sea evolve independently to camouflage themselves and lure prey with glowing tails before consuming them.

The analysis, focusing on Anguilloidei eels including various types, revealed multiple instances of independent evolution of tar-like pigmentation. This insight sheds light on the predatory behavior of these enigmatic deep-sea creatures.

New Insight Into the Mysterious Behavior of Deep-Sea Eels

The team described their findings in full in the journal Environmental Biology of Fishes, offering understanding of the elusive actions of these enigmatic deep-sea organisms, which often lack extensive research.

The research emphasizes the limited knowledge of the vast ocean ecosystem. Mike Ghedotti, the study's lead author and a marine biology professor at Regis University, highlighted the challenges in exploring the deep sea due to its cost and infrequent exploration compared to shallower waters.

While discovered at greater depths, deep-sea eels predominantly inhabit the ocean's Midnight Zone about 3,300 to 13,100 feet (1,000 to 4,000 meters) beneath the surface, a realm devoid of sunlight.

In this perpetual darkness, the eels' physical forms have evolved peculiarly, with the pelican eel's mouth being notably stretchy. Tracking their activities proves difficult. To illuminate their enigmatic conduct, researchers examined pelican eel skin tissue under a microscope, revealing unusual jet-black pigmentation on their bodies.

Research on various eel species, including deep-sea inhabitants like swallower eels and bobtail snipe eels, has revealed consistent ultra-dark pigmentation akin to pelican eels. Pelican eels, poor swimmers, potentially employ bioluminescent tails as lures to attract prey such as crustaceans and squid to their mouths, though their hunting behavior remains mostly unseen.

The effective hunting approach involves the use of ultra-dark pigmentation that absorbs bioluminescent light, causing the glowing tail tips of pelican eels and swallower eels to resemble solitary and captivating light sources in the dark-adapted eyes of potential prey. Once entranced prey is drawn near, the pelican eel employs its expandable mouth, five times its usual size, to consume the victim whole.

According to Mike Ghedotti, maintaining concealment of the predator's body beyond the lure is crucial during light-based prey attraction, which applies to various fish species using bioluminescence for different purposes.

Science Behind the Changing Coloration of Animals in Deep Sea

With the influence of light that penetrates the ocean water, the coloration of marine animals conforms to a consistent pattern based on depth. They start to camouflage within their environment that led them to change color and appearance.

Their color changes from blue near the surface to transparent with red stomachs in greater depths, and eventually red or black at the deepest parts, primarily for camouflage purposes.

For effective invisibility, an animal's color and brightness must match its background, but the variability of surrounding light hinders this. Water's filtering of light means red light is absent at deeper ocean depths, rendering red animals living there practically invisible due to their lack of contrast with the environment.

Color-camouflaging animals face challenges in matching both background and surrounding light, with seafloor dwellers benefiting from shared illumination, while aquatic swimmers encounter more complex lighting interactions, prompting ongoing exploration of marine animals' camouflage strategies.