Why manta rays have long tails remains a mystery

New research suggests manta ray tails may act as sensory tools.

A reef manta ray swims in the Red Sea, Egypt, on December 13, 2023. Photo by Tahsin Ceylan/Anadolu/Getty Images

By Laila Azzahra

Manta rays, with their horn-like facial fins and diamond-shaped bodies spanning nearly 30 feet, are some of the ocean's most unique creatures. Among their many fascinating features, one remains particularly puzzling—their long, whip-like tails. Unlike stingrays, which use their tails for defense or propulsion, manta rays' tails lack venomous spines and seem to serve a different purpose altogether.

Recent research suggests these elongated tails may function as sensory tools, helping manta rays and their relatives detect underwater threats. A study published in the Proceedings of the Royal Society B: Biological Sciences analyzed cownose rays, smaller relatives of manta rays, to uncover the secret behind their unusual tails. The findings point to the possibility that these tails act as fine-tuned antennae, capable of detecting subtle underwater movements.

The research, led by marine biologist Júlia Chaumel of Harvard University, uncovered surprising complexity within the tails of cownose rays. "The complexity inside the tail was super surprising," said Chaumel. "We had no idea that this huge structure had a sensorial function."

To explore the mystery, Chaumel and her colleague George Lauder studied cownose rays using specimens from Harvard's Museum of Comparative Zoology and two recently deceased rays. By creating three-dimensional micro-CT scans and examining tissue samples, they discovered that the tails were dotted with holes connected to the lateral line canal, a sensory system found in fish and amphibians.

The lateral line is a network of sensory organs that runs along a fish's body, allowing it to detect changes in water movement. While this system is usually most intricate near a fish's head, the researchers found that in cownose rays, it extends through the tail and branches out to pores in the skin.

The researchers believe this unique adaptation allows cownose rays to sense stimuli in their surroundings, particularly when they are vulnerable. For example, when cownose rays dive to the seafloor to feed on buried clams, they expose their heads and become easy targets for predators.

"A shark coming in from behind would cause these huge movements of water, which lets the ray know it’s time to zoom away," Chaumel explained. This sensory capability could provide the rays with a critical advantage, acting as an early warning system against potential threats.

Cownose rays belong to the myliobatid order, which also includes manta rays and other open-water species. Unlike stingrays, which typically have short, muscular tails equipped with venomous barbs, myliobatid rays have long, noodle-like tails that appear rigid underwater.

Matt Ajemian, a researcher at Florida Atlantic University who was not involved in the study, noted the striking difference in tail structure between these groups. "When you pick it up, it’s almost like a giant noodle, but in the water, it’s very rigid," Ajemian said. "Nobody really had a clue what these tails were being used for."

The study’s findings suggest that these tails may have evolved as sensory tools, but researchers are still investigating other possible functions. Chaumel’s team is now examining manta rays to determine if their tails share similar adaptations.

While the study sheds light on the sensory capabilities of cownose rays’ tails, it also raises questions about their adaptability. Ajemian’s team has observed rays in the wild with damaged or missing tails, suggesting that while the tails are useful, they are not essential for survival.

"We thought the tail was something that could easily be shed," Ajemian said. Even so, Chaumel believes the tails play a crucial role, especially in helping the rays navigate their environment and avoid predators.

Manta rays, the largest members of the myliobatid order, share many traits with cownose rays, including their elongated tails. These gentle giants spend most of their lives in open water, flapping their large pectoral fins to "fly" through the ocean. They are known for their long migrations and their filter-feeding habits, which involve scooping up plankton as they swim.

Researchers believe manta rays’ tails may also serve a sensory function, helping them detect changes in water flow or stabilize their movements, much like a kite’s tail. Chaumel’s team is currently analyzing manta ray tails to determine if they possess similar adaptations to those found in cownose rays.

The discovery of sensory capabilities in ray tails highlights the complexity of marine life and the many adaptations that have evolved to help species survive in challenging environments. Rays, with their unique physiology and behaviors, continue to captivate scientists and reveal new insights into the underwater world.

Understanding the purpose of these tails is not only important for scientific curiosity but also for conservation efforts. Many species of rays, including manta rays, are threatened by overfishing and habitat destruction. By uncovering more about their biology and behavior, researchers can better advocate for their protection.

The mystery of manta rays' long tails is far from fully solved, but studies like Chaumel’s bring us closer to understanding these fascinating creatures. As researchers continue to explore the sensory capabilities and potential functions of these tails, they are uncovering new layers of complexity in the lives of manta rays and their relatives.

Ultimately, this research underscores the importance of looking deeper into the natural world. What may seem like a simple anatomical feature can turn out to be a sophisticated adaptation, honed by millions of years of evolution to ensure survival in the vast, unpredictable ocean.

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