A seahorse is one of those evolutionary oddities that make you believe in unicorns, mermaids, centaurs and other cryptic chimeras. With an elongated snout and prehensile tail, seahorses conjure the illusion that they are a menagerie of animal parts.
These ocean anomalies are scientifically classified in the genus Hippocampus, which derives from the Ancient Greek “hippókampos,” meaning “horse” and “sea monster” or “sea animal.” According to Greek mythology, hippocamps (hippokampoi) were serpentine-tailed horses of the sea. In the Illiad by Homer, and the Trevi Fountain in Rome, a chariot of hippocamps is driven by Poseidon, the god of horses, earthquakes and the sea. During the Medieval and Renaissance periods, the hippocampus was depicted as a heraldic sea-horse with the head and neck of a horse, webbed paws instead of hooves and the tail of a fish, complete with fins.
Thanks to decades of scientific research and discovery, we know seahorses are neither horses nor monsters but 100% fish. They belong to a family of fishes called Syngnathidae—another Greek denomination—which includes seahorses, seadragons and pipefishes. All are characterized by the common trait of having a fused jaw.
Now we know the seahorse’s etymology and taxonomy. But where did they come from, how did they get here and why do they look so funny? Join me in taking a deep dive into the evolution of seahorses and learn how you can help save them by protecting their ocean habitats. Along the way, we’ll debunk misconceptions about these mythic beings while preserving all the magic!
What’s the Seahorse Origin Story?
Our journey begins in the Tunjice Hills of Slovenia, where beds of siltstone known as the Coprolitic Horizon—named for its abundance of fossilized animal feces, or coprolites—were unearthed by paleontologists between 1997 and 2003. The specimens included microalgae, mollusks, seagrass, jellyfish, insects and willow and pine tree leaves from the Miocene epoch (23.03–5.3 million years ago). The paleontologists determined that this site was once a shallow bay near a forest. After further excavations in 2005, they discovered it was also an oasis for seahorses.
In 2009, the beds of the Coprolitic Horizon became known worldwide for the oldest fossil record of seahorses. Recent genetic analysis reveals that seahorses have an Australasian origin, however. This is supported by the fact that the oldest and most diverse lineages occur in Australia and the Indo-West Pacific, i.e., Indonesia.
So, what were seahorses doing in Slovenia? And how did they spread across the planet?
How Did One of the Ocean’s Worst Swimmers Spread Across the Globe?
Seahorses are regarded as one of the slowest-moving fish species in the ocean. Unlike most fish, which have caudal fins for a tail, seahorses have a prehensile appendage, which functions as an anchor. Seahorses flutter their dorsal fin 30–70 times per second to propel themselves, and they steer and stabilize with a set of pectoral fins on either side of their head.
This method of transportation is extremely energy intensive, so seahorses evolved to work smarter, not harder. By coiling their tail around a piece of floating seaweed, seahorses can drift along ocean currents with little to no exertion. Scientists reasoned that this “rafting” behavior facilitated the long-distance dispersal of seahorses around the globe.
Seahorses didn’t always possess such a unique body shape, however. To understand how their iconic S-curve developed, we must go back about 25 million years, near the end of the Oligocene epoch. The Australian tectonic plate under what’s now New Guinea pushed northwards, colliding into a jumble of plates under the modern-day Philippines, as well as the southeast tip of the Eurasian plate. The enormous geological impact transformed a deep channel between the continents into many large, shallow seas.
With the seabed closer to the surface, it became exposed to more sunlight, accelerating photosynthesis. Seagrasses proliferated and expanded their range, allowing different kinds of life to flourish. Scientists hypothesize that the conditions in these seagrass beds catalyzed an anatomical shift in some Syngnathids to evolve from a long-and-straight horizontal posture like that of a pipefish into the upright posture we see in seahorses today. The vertical seagrass blades provided the perfect camouflage for their upright bodies, affording them protection from predators and an improved ability to ambush prey.
Why the Long Face?
Although its upright posture slows it down when it comes to swimming, the seahorse’s peculiar head, neck and trunk alignment has made it surprisingly fast at snatching prey. In one swift, trigger-like movement, these voracious carnivores can strike in as little as one millisecond with a 90% success rate. To put that into perspective, orcas, or killer whales, have an 80% success rate, sharks 60% and jaguars 70%.
The seahorse’s prehensile tail allows it to grab onto seagrass instead of constantly treading water, making stalking its next meal more efficient. Like a vacuum cleaner, it sucks in water, trapping a variety of floating and swimming organisms inside its long, toothless snout. The seahorse’s diet includes shrimp, plankton, copepods, tiny crustaceans, nematodes, gobies and fish larvae.
Seahorses don’t have stomachs, and their digestive systems process food so quickly that they must continually graze to survive. Adult seahorses eat 30–50 times a day, and seahorse fry (baby seahorses) consume 3,000 pieces of food per day!
Using a series of mathematical model simulations, biologists Sam Van Wassenbergh, Gert Roos and Lara Ferry sought to find an adaptive explanation for the horse-like shape of seahorses. In contrast to pipefish, seahorses are “tail-attached, sit-and-wait predators,” meaning they strike from an anchored position.
The team’s experiments revealed that the sharper the angle between the head and trunk, the greater the distance the seahorse can strike from and the greater the volume of water it can draw in. This was a desirable trait, and more curved seahorses were naturally selected, further contorting the shape of these fish over many generations.
Why the Square Tail?
Another peculiar trait of seahorse morphology is the structure of the tail. While several animals have prehensile tails—such as monkeys, opossums, chameleons and even some species of pangolins—the cross-section of a seahorse tail is a square prism, not a cylinder like the others.
Determined to understand why this structure evolved, a team of American and Belgian researchers 3-D printed prototypes of square and cylindrical seahorse tails and applied various degrees of crushing and twisting pressure. They observed that the rounded tail had a greater range of movement but lacked strength and durability, resulting in it being squashed under pressure. In contrast, the square tail repelled vertebral fracture by flattening out and diffusing harmful impacts across a surface area of overlapping plates.
In nature, these mechanics translate to a range of advantages for seahorse survival. For example, the tail’s elasticity and bony armor help it withstand the jaws of some predators. And compared to a circular tail, the square tail affords more contact points with surfaces, making it a more dexterous gripping device. These qualities are so extraordinary that scientists are working to develop robotic applications inspired by seahorse anatomy for search-and-rescue missions, surgeries and more.
Are Seahorses Monogamous?
Male seahorses take commitment so seriously that they bear the burden of pregnancy for their mates. Unfortunately, the same cannot be said for their female counterparts. Until recently, seahorses were generally assumed to be monogamous for life, but researchers from the Chinese Academy of Fishery Sciences discovered that isn’t always true. They found that female seahorses maintain sexual fidelity to their partners as long as their pair bonds remain unbroken.
But in instances of physical separation or the declining health of her partner, the female will switch mates, and her courtship with the new partner may even take place during the pregnancy of her original partner. From a competitive evolutionary perspective, the female could lose the opportunity to mate with a potentially fitter male if she were to repair a broken bond. Nature truly is a harsh mistress.
How Rad Are Seahorse Dads?
Remaining faithful to one partner does have certain advantages, however. Monogamous pairs have more time to undergo more pregnancies during a single mating season, which leads to greater reproductive success. Timing is everything in the seahorse realm, as fertilization requires precision and synchronicity.
In preparation for the main event, pairs reinforce their bonds through daily greetings lasting from a few minutes to several hours. Twice a day, they will court each other by dancing in circles, interlocking tails and sometimes even changing colors. This routine is rehearsed until the duo is completely in sync. Then the crescendo—a passionate 10 seconds (or less) of intercourse—followed by the denouement, when the female delivers hundreds to thousands of eggs into the male’s “brood pouch” using a tube called an “ovipositor.”
When the sand settles and the male has restored his stamina, he assumes the role of dutiful dad. After roughly two weeks of incubation (up to four for larger seahorse species), the male experiences powerful contractions and then expels fully developed fry into the water. Tiny and defenseless, less than 0.5% of the new generation of seahorses make it to adulthood.
Do Seahorses Need Saving?
The survival rate of seahorses is determined by external factors as well. The International Union for Conservation of Nature (IUCN) lists several seahorse species as vulnerable to extinction. Many, if not all, of the 47 known seahorse species—14 of which were identified only in the 21st century—are in decline worldwide.
Seahorses are flagship species and indicators of ecosystem health for some of the rarest coastal habitats on Earth. Sadly, they face many threats, including climate change, habitat loss, pollution, bycatch from overfishing—which accounts for 70 million deaths annually—and the illegal wildlife trade.
The greatest number of seahorse species is found in the marine biodiversity hotspots of the central Indo-Pacific region. The Sulu-Celebes (Sulawesi) Sea region—shared by Indonesia, Malaysia and the Philippines—is an area of unprecedented ecological value. It is also the epicenter of exploitation. From June 2003 to September 2021, 452 illegal wildlife seizures were recorded. By Family, seahorses were the largest quantity of confiscated individuals (12,041), followed by turtles (Geoemydidae, 5,556; Cheloniidae, 2,546) and pangolins (5,797).
Along with shark fins, rays, abalone, sea cucumbers and fish maw (dried swim bladder), seahorses are a prized marine product, consumed as symbols of wealth and status, and dried as a key ingredient in Traditional Chinese Medicine (TCM). TRAFFIC, the Wildlife Trade Monitoring Network, reports that high demand, especially from East Asia, has resulted in illegal and unsustainable harvesting and exportation in Africa.
The TCM trade poaches in excess of up to 150 million seahorses a year; the curio trade, which targets marine species to be sold as souvenirs to tourists, takes about one million seahorses from the wild each year; and the exotic pet and aquarium trade accounts for an estimated one million seahorses trafficked per year—many of which do not survive beyond six weeks.
Seahorses that evade the illegal wildlife trade must navigate an ever-accumulating ocean of plastic pollution, which kills approximately 100,000 marine mammals annually. The Ocean Conservancy reports that 11 million metric tons of plastics enter our oceans every year, in addition to the estimated 200 million metric tons that are currently circulating through our waterways.
This infamous photograph taken by The Natural History Museum’s 2017 Wildlife Photographer of the Year, Justin Hofman, illustrates how the fate of seahorses is inexorably tied to the future of our marine ecosystems:
What Are Some Sustainable Solutions?
Tackling the illegal wildlife trade is no small feat. Fortunately, conservation conveners: World Wildlife Fund, TRAFFIC and the International Fund for Animal Welfare (IFAW) joined forces to help keep wildlife #OfflineAndInTheWild with the creation of The Coalition to End Wildlife Trafficking Online. As a Cyber Spotter, you can join the Coalition’s critical force of citizen scientists to help identify and report illicit animal products across e-commerce sites and social media platforms.
When traveling, do not buy animal, coral, shell, hardwood or live plant products. Check out WWF’s Buyer Beware recommendations to determine whether the product you’re looking at is illegal or sustainably sourced. You can also symbolically adopt a seahorse through WWF! Every donation helps save endangered wildlife, protect fragile ecosystems and build a future where people live in harmony with nature.
As for mitigating marine pollution: “Using less plastics when you can remains the number one advice for everyday consumers,” says Eirik Lindebjerg, WWF’s Global Plastics Policy Manager. That means switching to reusable water bottles and shopping bags whenever possible and choosing sustainable alternatives like bamboo straws and biodegradable plates.
Use your voice and demand global leaders and policymakers ban single-use plastics, sign WWF’s petition No Plastic in Nature and educate yourself with WWF’s report on the impact of plastic pollution. For more green tips, visit our travel blog Good Nature and read “The Truth about Plastic Pollution and How We Can Stop It.”
Where in the World Can You See Seahorses?
Preferring calm, shallow waters, seahorses thrive in seagrass beds, mangrove estuaries and coral reefs in temperate and tropical waters worldwide. In our Daily Dose of Nature Webinar, “Seahorse Truths and Tales,” Nat Hab Expedition Leader Melissa Silva shares her favorite seahorse species and where they can be found. Watch the video below to learn about species like Hippocampus nalu, a newly discovered pygmy seahorse from South Africa, Guttulatus, a spiny seahorse that lives in UK seas and Hippocampus zebra, endemic to northern Australia’s Great Barrier Reef.