The ocean’s dark depths remain one of the greatest mysteries on Earth. Thousands of feet below the surface, there could be any number of discoveries, and one example is the “glow-in-the-dark” sharks found in 2020. Their discovery has provided insight into the bioluminescent world of the deep ocean, and there’s more to be uncovered than ever before.
Bioluminescent Sharks
In 2020, researchers on a fisheries research vessel used a commercial-scale trawl net to survey species inhabiting the ocean’s mesopelagic or “twilight” zone – roughly 660 to 3,300 feet below the surface. During their expedition, three bioluminescent shark species were brought up in nets off the east Coast of New Zealand. The resultant study, published in Frontiers in Marine Science, provided the first-ever documentation of bioluminescence in sharks.
The Kitefin Shark
The Kitefin shark (Dalatias licha), one of the three sharks discovered in 2020, is the largest luminous vertebrate, measuring up to six feet. While the species had been known since the 18th century, it was not until now that scientists saw it glow for the first time. It is described as having brown-black skin and a large, gaping eye, and it glows blue in color. It is one of 57 shark species that have bioluminescent skin.
Other Luminous Sharks
In addition to the kitefin shark, researchers also documented that the blackbelly lanternshark (Etmopterus lucifer) and the southern lanternshark (Etmopterus granulosus) also glow in the dark. Blackbelly lanternsharks are small, roughly 47 centimeters long, and are said to live in shallower, southern waters at a depth of 150 to 1,250 meters. The southern lanternsharks are slightly larger, measuring roughly 60 centimeters long, and they are commonly found in the southeast Pacific at a depth of 220 and 1,460 meters.
How Bioluminescence Works in Sharks
Bioluminescence typically occurs due to luciferin, a chemical compound that glows when it interacts with oxygen. However, research suggests these sharks might produce light through a different biochemical mechanism – hormones. The study’s marine biologist and lead author, Jérôme Mallefet, suggests that these sharks use two to three hormones to trigger or turn off their bioluminescence. He further states, “Once they light up, they cannot change rapidly.”
The Purpose of Bioluminescence
The exact reasons for bioluminescence in these sharks are still being studied. Because bioluminescence is usually a survival mechanism, scientists question its use in sharks, as they are considered apex predators. Thus far, scientists theorize that the sharks’ glowing bellies could serve as camouflage, making them harder to spot from below, and, with the kitefin shark in mind, it could illuminate prey on the seafloor.
Other Bioluminescent Sea Creatures
Bioluminescence is relatively common in the depths of the seas, with many species exhibiting luminescent behaviors. These include fish, squid, coral, turtles, eels, stingrays, and sea horses. Bioluminescence can show various patterns, distinguishing males from females, helping animals blend into their environment, and, in some species, facilitating mating.
A Realm of the Unknown
The deep sea has hardly been explored, with trenches and entire ecosystems never captured on film or studied. This is likely because of extremely cold water temperatures and difficulties in technology and equipment that can withstand deep-water pressure. However, as technology advances and more discoveries are made, researchers and conservationists seek to explore the ocean’s floors.
Protecting the Deep-Sea Environment
The discovery of these glowing sharks highlights the importance of protecting deep-sea environments. These unique species and their habitats, which have yet to be studied and could add to our growing knowledge of marine life, are particularly vulnerable to human activities, such as deep-sea mining and pollution, as well as changes in water temperatures due to climate change (which results in habitat and food source losses).
The Bizarre Deep-Sea
Besides bioluminescent sharks, the deep sea is home to many other bizarre creatures. The deep sea is home to anglerfish, such as the Frogfish, sea cucumber–like the Pink See-Through Fantasia, Isopods–such as the Munnopis and Giant isopods, jellyfish, and snails. With each discovery, the incredible adaptations that life has developed to thrive in this extreme environment can be studied and protected.
New Species in the Deep Ocean
Over the last three decades, two new species living in the ocean’s deep waters have been discovered: Bathydevius caudactylus, a sea slug, and a pocket shark. The pocket shark, which measures 5.5 inches and resembles a sperm whale, was found in the Gulf of Mexico, while the sea slug, the size of an apple, was found offshore of Monterey Bay. Both are bioluminescent.
The Future of Deep-Sea Exploration
Since continued exploration is essential for understanding the biodiversity and ecological mechanisms in the ocean’s depths, scientists are continually developing new ways to explore the sea. For example, marine biologist and explorer-photographer David Gruber teamed up with roboticist Rob Wood from Harvard University to create a “one-person submarine suit” that allowed them to explore the deep sea safely and where they could interact with marine life without harming it.
Illuminating the Deep Dark Ocean
With the discovery of the shark species and other creatures living in the depths of the widely unexplored ocean, scientists and the public are beginning to see the importance of marine conservation and advanced technologies. Using both will allow us to explore the sea, learn from it, and simultaneously protect it. By studying unique ecosystems, we better understand the natural world far beyond what was imagined 50 years ago.
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