One of the most unusual and heavily populated communities of seahorses on the globe lives in a land-locked lake in the Bahamas, yet this aquatic marvel is also threatened by human activities.

A unique body of water 1.5 km wide and 2.5 km long with a maximum depth of 13 meters is hidden away in the north of Eleuthera, one of the Bahamas’ largest islands, and is blocked off from the sea by a strip of land just a few meters across. Sweetings Pond is how the locals refer to it, and it is home to a unique and unusual colony of seahorses that has been entirely concealed from the rest of the world until now. However, human activities have put this lagoon-like lake in jeopardy, and it must be protected if its fascinating species are to remain.

Hidden In Plain Sight

If you go snorkeling at Sweetings Pond in quest of seahorses, you might assume you’ve been misled about their existence. As you carefully examine the shallow borders of the lake, gazing intently at the golden algae beds, you begin to believe that you are entirely alone, but then you notice one out of the corner of your eye. A tiny seahorse emerges through the seaweed with its short nose poking inquisitively.These tiny animals (only ~10 cm long) are masters of disguise, flawlessly blending in with their environment, but once you’ve discovered one, you’ll be able to find many more. When you take a second glance around, you’ll notice that you’ve been surrounded by them the whole time. You’ll probably see more seahorses here than you have in your whole life before long.

How Did They Get There?

The fact that this bunch of seahorses exist at all is the most unexpected aspect of their existence. It seems inconceivable that a purely marine creature could live, much less flourish, in a landlocked lake. Sweetings Pond, despite its geographical isolation from the sea, is actually much more connected to the sea than it looks. It’s an ‘anchialine pool’, which means it’s made out of saltwater that flows through the porous limestone rock in the ground that separates the two pools of water. It’s still a mystery how the seahorses were capable of going from one to the other. It’s possible that some juveniles were formerly able to swim through the limestone matrix, that they were left behind by prior sea-level changes, or that they were purposefully placed there by an ancient generation of Bahamians. All we know for sure is they’ve arrived, and there are a huge amounts of them.

Baby Boomers

For the past five years, Dr. Heather Masonjones of the University of Tampa in Florida has been monitoring the seahorse population in Sweetings Pond. When she first visited Eleuthera to see the location for herself, she was astounded by the sheer number of seahorses that lived there. The famous ‘mark and recapture‘ technique of catching a seahorse dying part of its skin and releasing it to estimate numbers indicated that there were hundreds upon thousands of them in the lake. Dr. Masonjones isn’t sure how many there are since these seahorses are unusually mobile and move around a lot, but she’s convinced it’s the world’s most densely inhabited seahorse colony. This is likely due to their seclusion, which has resulted in a scarcity of predators (except from a few octopuses), resulting in a greater juvenile survival rate.

New Evolutionary Path

Dr. Masonjones was perplexed by the seahorses at Sweetings Pond not just because of their abundance, but also because she couldn’t figure out which species they were. Slender seahorses (Hippocampus reidi) and lined seahorses (Hippocampus erectus) are the two Atlantic seahorse species that attain this fairly big size. To her, it appeared as though the two species had combined. As a consequence, her initial hypothesis was that the two species had mixed in the pool due to hybridization, but genetic research revealed that this was not the case. The seahorses were lined seahorses, but not in the way we’re used to seeing them.

Their physical modifications are due to the fact that they have gradually adapted to their particular habitat through time. To begin with, their tails are significantly shorter and more stubby than those of other lined seahorses. This is likely due to the fact that their isolated environment lacks the currents of the open ocean, making swimming considerably simpler, which also explains their busy and nomadic existence. Second, their skulls are elongated and thin, however the cause for this is less apparent. The more the team investigates these creatures, the more they don’t match with what they know about this species. This only leads the researchers to suspect that these seahorses are on their way to creating a whole new species.

Facing New Threats

The lined seahorse, like the majority of seahorse species, is vulnerable to extinction. Across 15-20 million distinct seahorses are traded annually around the world, although exact figures are difficult to come by because most are caught illegally. They are either killed and dried for use in traditional remedies, or they are sold as pets in the aquarium trade. This is why maintaining a healthy self-contained population is critical to the species’ existence. Unfortunately, experts believe that some seahorses have already been removed from the lake, and the risk of this continuing is considerable because these individuals are one-of-a-kind and hence extremely valuable.

Of real concern is the fact that seahorses rely on monogamous mating partners, therefore making them highly susceptible to physical disruption. When they are separated, whether by clumsy visitors or poachers, the population’s capacity to survive is severely harmed. There is also worry that agricultural practices in the region are expanding closer to the pool’s boundaries, posing a risk of chemical run-off contaminating the water quality.

Protecting The Pond

The seahorses at Sweetings Pond have long been shielded by their obscurity. They faced no imminent risk since no one knew they were there. For a long time, researchers and locals managed to keep its location a secret, and even as more people became aware of it, many still had no idea which island it was on. However, because the location has risen in popularity among visitors and the residents have become well-known in the field of marine biology, everyone now knows where they are.

As a result, the Bahamas National Trust is attempting to do the exact opposite of keeping the seahorses hidden in order to safeguard them. Sweetings Pond is being designated as the new ‘Seahorse National Park’, in order to assist establish new legislation to adequately preserve them. They are secretly optimistic that they will be able to make it a UNESCO World Heritage Site. If they succeed, these unique seahorses will be safe and secure, even if they are attracting more attention than they would want.