Revealing the hidden kingdom of seahorses
On a Bahamian island, in a landlocked lagoon, the planet’s densest collection of seahorses is offering scientists new insights into the secret lives of one of the world’s most mysterious fish.
Heather Mason was used to her quarry being much more elusive. Seahorses are often only a few inches long, can change colors like a chameleon, and rarely gather in groups. Their ability to disappear into their habitats—tropical seagrasses, mangroves, and reefs—helps keep the slow-swimming, largely defenseless fish from becoming an easy meal. That makes devoting a career to studying them, as Mason, a marine ecologist at the University of Tampa, has done for decades, an exercise in patience. But when she first snorkeled the pristine waters of Sweetings Pond on the Bahamian island of Eleuthera, she found herself in a seahorse-studded heaven.
Over her first weekend in the pond’s clear blue water, in 2013, she counted 16 seahorses—far more than the one or two she’d be lucky to spot during multiweek research trips along the coast of the Bahamas. Immediately, Mason realized that the mile-long Sweetings Pond was special: a safe haven for one of the ocean’s most enigmatic creatures. “It was life-changing, as someone who looks for seahorses in the wild,” she says. And this rare window into their existence has revealed fascinating behaviors.
Mason’s life-changing moment can be traced back some 7,000 to 10,000 years. That’s when scientists estimate Sweetings Pond filled with ocean water that filtered in from nearby Hatchet Bay (roughly one mile east) through underground cracks and holes. The landlocked saltwater lagoon, in turn, became a fortress for brittle stars, spider crabs, octopuses, bioluminescent plankton, and, of course, the seahorses. A refuge where several of the species’ regular predators—skates and rays, tuna, sharks—can’t possibly break in. “It’s an island on an island,” explains Mason.
Inside Sweetings Pond, Mason found seahorses as singular as the body of water itself. With oddly long snouts, squat bodies, and short tails, they differed radically from anything she had seen since she’d begun studying the creatures in 1990. She and her collaborator, evolutionary biologist Emily Rose, classified them as lined seahorses, Hippocampus erectus—but the seahorses of Sweetings are on the path to becoming their own subspecies. Observing so many of them in isolation offers “an opportunity to study evolution in action,” as Mason puts it.
But the biggest breakthrough came in the dark. Botanist Ethan Freid, who works for the Bahamas National Trust, the nonprofit that manages the country’s national parks, had originally learned from locals about Sweetings’ seahorse population and contacted Mason. After the marine ecologist’s initial visit, Freid had an idea: What if they explored the pond at night?
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Under a starlit sky, Mason and Freid donned scuba gear with dive lights and waded into Sweetings. They could barely believe their goggled eyes. “I ran my light across the bottom, and it was like road reflectors at night,” Mason recalls. “You could see seahorses lit up everywhere.” Freid describes the scene as resembling “a seahorse rave.”
On a later trip, over the course of four days and nights Mason and a research team documented 800 seahorses—roughly five times as many as they’d counted during daylight hours in the same limited area. Some were just a few days old—a surprise, as tiny juveniles are rarely seen, and little is known about what happens to newborn seahorses in the wild. Most striking was the difference in the fish’s behavior. “During the day, the seahorses are face down; they’re cryptic, they’re hiding,” Mason says. “And at night, they come up higher in the vegetation, so they’re upright and obvious.”
That nighttime rave, as Freid puts it, doesn’t necessarily mean all seahorses are nocturnal; Sweetings is isolated, and its seahorses’ behavior may be unique. Nor does the research team understand why these seahorses spend their days face down, though it’s possible they’re resting after a night of eating plankton and small crustaceans—or hiding from birds that feed on them in shallow waters. Still, the overnight survey and subsequent research resulted in the first published paper on seahorses’ nocturnal lives. In 2023, the team reported that Sweetings Pond is home to the highest known density of seahorses in the world—a number in the thousands.
At the time of the dark-of-night discoveries, the pond was still open to the public. But Mason’s years of research helped the Bahamas National Trust petition the Bahamian government for protection. Two years ago, Sweetings Pond became part of the newly created Seahorse National Park, a preserve that spans 548 acres and includes Hatchet Bay Cave, one of the longest dry cave systems in the Bahamas. The park closed to the public a few months later, and the trust now raises funds and prioritizes conservation over access.
Mason is still plumbing the data she collected over a decade and hopes to return to the pond. Answers to questions about courtship rituals, the reason for male pregnancy, and where seahorse babies go after being born may float in the pond’s placid waters. Sweetings might also show how the species responds to rising water temperatures.
“Before this project, I would have hesitated to ever use this word about a system, but Sweetings Pond is magical,” Mason says. “There is a sea of questions to answer.”
For now, the seahorses of Sweetings Pond are safe in their island inside an island and can keep their secrets a little while longer.
