National Museum of Natural History

Scientists Brave One of the Darkest Places on Earth for Rare Predatory Worm

Staring into the mouth of flooded cave passages on the islands of the Turks and Caicos. Hidden cave pools are illuminated by dive lights and photo flash. (Joost Daniels, Monterey Bay Aquarium Research Institute)
Staring into the mouth of flooded cave passages on the islands of the Turks and Caicos. Hidden cave pools are illuminated by dive lights and photo flash. (Joost Daniels, Monterey Bay Aquarium Research Institute)

In 1982, marine scientists from Texas A&M led an expedition to a series of underwater caves in the Turks and Caicos. They discovered a vibrant ecosystem teeming with life but what they didn’t expect to find in these shallow waters was a rare species of scale worm that was far removed from its deep-sea relatives. Why and how it got there remained a mystery.

Nearly 40 years later and armed with modern genetic technology, Smithsonian marine biologist Brett Gonzalez and his team revisited the caves to pick up where the original researchers left off. They spent 10 days exploring one of the darkest, most extreme environments on Earth to learn more about life in caves and this perplexing species of scale worm.

The watery underworlds of the Turks and Caicos

Trees line the entrance to an underground cave.
The entrance to an underwater cave system explored by Gonzalez and his team during the research trip. (Brett Gonzalez, Smithsonian Institution)

The dense jungle of the Turks and Caicos, with its rash-inducing flora, venomous spiders and bountiful mosquitos holds little threat when compared to the caves below. These watery underworlds are pitch-black, claustrophobia-inducing mazes to the unprepared.

“It’s the darkest place you’ve ever been in,” says Gonzalez. “So dark, you only know your hand is in front of your face because you’ve put it there.” To navigate the inky blackness, divers are aided by dive lights and carefully placed nylon guidelines mapping the way back to the cave’s only exit.

“Caves are unforgiving,” stresses Gonzalez. “Letting your guard down, even for a second, may spell certain disaster or death if you’re not prepared.

A Diver in a dark, underwater cave.
Brett Gonzalez donning his diving gear before entering the water in one of the underwater caves on the island. ((Joost Daniels, Monterey Bay Aquarium Research Institute) )

If the darkness weren’t bone-chilling enough, there is always the potential of getting stuck while exploring the tunnels and tight crevasses of the caves. And if the divers lose focus, their fins can kick up vision-blocking underwater silt-storms that make finding the way back to the surface nearly impossible.

But Gonzalez and his team carefully train for these perils. “When I’m in a cave, I don’t have to worry about the unknowns, like currents, storms or large predators as you would when diving in the open ocean,” says Gonzalez. “We plan and prepare for each dive, including worst case scenarios.”

Flooded evolutionary microcosms

Despite the dangers, scientists including Gonzalez continue to dedicate their careers to exploring these treacherous environments because they are home to species that help biologists better understand adaptation and evolution.

“Cave environments are essentially evolutionary microcosms,” explains Gonzalez. “They force noticeable changes in response to the demands of the habitat, making it easy to connect an animal’s adaptations to environmental pressures.”

Interestingly, some cave species show less adaptation than others, as if they are in an intermediate phase of their evolution. This transitional state is something rarely seen in other habitats.

The flooded caves of the Turks and Caicos are a prime example of how an extreme environment can force adaptation. To combat the lack of light, limited food supply and isolation of the caves, many of the inhabitants traded their sight for enhanced sensory appendages, developed extremely efficient ways to store calories and have become the perfect hunters for their limited prey.

The new mission

When Gonzalez and his team donned their wetsuits and dove into the submerged cave, they hoped to finally unravel several longstanding evolutionary questions about cave life that had been left largely unanswered since the 1982 expedition.

Orange marine worm on black background.
Scale worm, Pelagomacellicephala iliffei, was first discovered by Thomas M. Iliffe in 1982. A dislodged scale can be seen above the animal. It was one of the main species Gonzalez was after on his trip. (Jørgen Olesen, Natural History Museum of Denmark, University of Copenhagen)

Gonzalez’s sought-after scale worm puzzled scientists since its discovery. Its closest known relatives are found thousands of meters below the ocean’s surface. Not in the shallow pools of a tropical cave.

“A lot of animals that live in these caves have their closest relatives in the deep sea, and share similar adaptations,” says Gonzalez. “I’m trying to understand how body plans, behavior and genetics change in response to these extreme environments.”

After 10 grueling days in the caves, Gonzalez found his scale worm. “It always seems to happen that way with field work, things come together at the last possible moment,” Gonzalez reminisces.

A fruitful endeavor

In addition to Gonzalez’s scale worm, the team brought back numerous samples of other animals, discovering several new species in the process.

Gray and orange crustacean on black background.
Like the one seen here (Lasionectes entrichoma), a new remipede species was found during the expedition. (Jørgen Olesen, Natural History Museum of Denmark, University of Copenhagen)

Most excitingly, the researchers found a new species of a blind crustacean called a remipede which is only found in these types of caves. Using high-speed videography, the team captured swimming behavior of both scale worms and remipedes to compare locomotor mechanisms and efficiency of their paddle-like appendages.

This expedition contributed to a larger effort — the Global Genome Initiative — to catalog half of the globe’s genomic diversity by 2022. Specimens from this trip are preserved in the Smithsonian’s high-grade, genetic tissue collection, or Biorepository, and are available to scientists around the globe for study. They are a priceless record of life on Earth at a time when its ecosystems are undergoing drastic changes and many of these animals may soon be lost for good.

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Raven Capone Benko

Raven Capone Benko was a science communication and policy fellow with the Smithsonian’s Office of Government Relations. She holds a B.S. in Biology and a B.A. in Environmental Policy from Western Washington University where she conducted research in harbor seal ecology. She has also conducted research on the responses of larval fish to environmental stressors with NOAA. Raven is a passionate advocate for science-based policy and science communication and aims to streamline engagement between scientists, policymakers and the public.

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