Seeing Seahorses

Have you ever seen a seahorse? If you dive in tropical or temperate waters, you've almost certainly swum right past them without knowing. And it's not just you. Seahorses are among the most elusive creatures in the ocean. In addition to their diminutive size and stealthy movement patterns, they are masters of disguise who can take on the textures and colors of their surroundings. They are also some of the most fascinating subjects you'll ever meet, which makes it worth spending a little time seeking out these weird little fish.

Yes, sea horses are fish. They have gills, swim bladders, fins and other distinguishing features shared by all members of the Osteichthyes class of bony fishes. But they also exhibit some marked differences from their finned cousins. Instead of scales, they have exoskeletons made up of hard bony plates that fuse together like biological body armor. This hardening makes seahorses unpalatable to some would-be predators, but there are still plenty of crabs, rays and some fish that would love a seahorse dinner. To avoid this fate, they rely on their ability to blend in.

Seahorses have an almost uncanny ability to change colors and skin patterns. Their skin contains tiny organs known as chromatophores, which are light-reflecting cells that contain liquid pigments. By shifting the size, shape and orientation of these cells, seahorses can mimic and blend into their surroundings. This not only helps them avoid the wary gaze of would-be predators, it's also a major advantage in their own hunting endeavors.

Seahorses are some of the slowest swimmers in the oceans, but this doesn't stop them from being one of the most efficient predators on earth. Even with their small dorsal fins fluttering as fast as 60 times per second, they reach a top speed of just about five feet an hour. So instead of trying to chase down a meal, they lie in wait. And this is something they are really good at. Seahorses have excellent eyesight, which helps them pick out the tiny crustaceans that make up most of their diet. For even better spotting, their eyes can work independently, with one eye facing forward and the other backwards to extend their range of vision.

Once they lock in on their tiny prey, a seahorse will either wait for it to come within range, or move very slowly in pursuit. And seahorses catch their prey about 90 percent of the time, which is a far higher success rate than almost any other hunter on land or water. The key to their prowess is in the snout.

The seahorse's vertical swimming style and elongated snout allow it to capture prey in a unique manner. Once they are in range, a seahorse will make a lightning-quick snap of its elongated neck. This generates a powerful suction that sweeps the prey into the seahorse's open mouth. And there’s another trick of nature that works in the seahorse's favor. Scientists who study this sort of thing have determined that the distinctive shape of the seahorse head allows it to move through the water without creating the type of disturbing pressure waves that would warn potential prey of an approach. It's a good thing that seahorses are lethally-effective hunters, because they eat a lot. Youngsters, known as fry, consume up to 3000 bits of food daily, while full-grown adults still feed some 30 to 50 times a day.

Those oversized tails that slow the seahorse when swimming are actually pretty useful for other things. They can use it to grasp things and anchor themselves to seagrass, mangrove roots or the fronds of soft coral. This comes in handy when they need to hold on against surge and currents as they wait for food to be washed their way. A pair of seahorses will sometimes link tails when swimming, or during one of the daily courtship rituals that these monogamous fish are known for.

Another advantage of the seahorse's gripping tail comes when it's time to relocate at a faster pace that swimming allows. By grabbing on to a bit of floating debris such as a drifting leaf, a seahorse can hitch a free ride on ocean currents. In some cases, a seahorse will commute back and forth between two stations by working with the ebb and flow of the tides.

Seahorses mate for life, and the dads take on the most demanding child-rearing task of any male in the animal kingdom. When it's time to make babies, the female will approach the male, and both signal their willingness with a specific color change. The male begins to circle the female, then both may spiral together and eventually link tails. This undersea dance can last for up to an hour, during which time the mom transfers her eggs to dad. Yep, the seahorse is the only animal known to practice a true reverse pregnancy.

Once the eggs are secured in dad's special pouch, he self-fertilizes them and begins a pregnancy that can last from two to four weeks. Smaller species have brood a hundred or so eggs, while the larger seahorses nurture litters of up to 1,500 babies, which are released in live birth involving a lengthy series of contractions. So, for once it's the guys who have it rough in childbirth.

Finding any seahorses can be a challenge, but the smallest members of the family — the pygmy seahorses — are so diminutive and well-camouflaged that their very existence wasn't known until 1969, and six of the seven known species weren't discovered until the early 2000s. With the smallest of these fish growing to less than a half-inch in length, it's not surprising that they remained unknown to science. Now that their presence is known, the biggest aid in locating them is known where to look. Unlike their larger cousins, which can live on reefs, seagrass beds or mangrove forests, the pygmies prefer to nestle into the branches of a soft coral, and can be very specific about the species of coral they prefer. Once settle in, they rarely move. So once a pygmy is located, there's a good chance of finding it again. For the average diver, the best chance of seeing a pygmy is to work with a dive guide who knows the waters, and can point out these elusive creatures which hide in plain sight.