Seahorses are four animals in one

From my many years of scuba diving, I’ve found countless debris cast off or lost by humans to the underwater world.

Landfill items include the gross (used adhesive bandages, condoms), the “no-surprise-there” (flip-flops, sunglasses, fishing paraphernalia), the odd (a folding chair, CDs), the endless plastic shrapnel (drink bottles, straws, kayak paddles, bottle caps, toys, credit card room keys), the rare ($1 bills), and the absurd (desktop computer system, vacuum cleaner). Even so, I wasn’t the least bit blasé after discovering a couple of horse heads buried in a tangle of algae.

No chess pieces here, these living horses (about 5 inches long but they can grow to 12 inches) of the sea have recently ridden into town on the back of the El Nino. Called a Pacific seahorse (Hippocampus ingens), they are not entirely unknown in Southern California, with small numbers secreted to gentle waters that fill local bays and lagoons.

In contrast, the open coast’s strong surges and currents can be inhospitable to the delicate steeds and interfere with prey capture, but more on that shortly. A look at the horse’s prehensile (instead of fin-shaped) tail and it’s obvious that this is a fish built to sway, not swim. Disproportionally tiny and nearly invisible fins reinforce that the seahorse is not one to buck the currents.

Instead, a casual observer might assume a hungry seahorse remains hooked onto substrate while wafting to and fro in a sort-of torpor waiting for hapless prey to blunder into its mouth. This isn’t the case at all.

The entire trajectory of seahorse prey to seahorse gullet is astonishing, like a snail winning a race against a cheetah. The seahorse plays the role of the snail, and the cheetah is played by its prey, a tiny, planktonic crustacean called a copepod (the size of two grains of salt). When sensing imminent attack, as determined by the merest hint of water movement around it, a copepod can rocket away. How fast? Well, a cheetah, the swiftest land animal, reaches speeds of about 75 mph but would have to clock in at more than 1,000 mph to attain the speed of a frightened copepod. And yet, a copepod almost always loses to a seahorse. 

Once a copepod enters a seahorse’s sphere of influence, the seahorse rotates its head at whiplash speed to bring the mouth near to the prey. The vacuum-shaped snout sucks into the mouth a great volume of water along with the wee crustacean. The seahorse owes its extraordinary success to having a uniquely shaped head that reduces water movement in front of the mouth. Having a highly flexible neck allows the angle of the head to be tweaked to pinpoint the nose to the prey. It is this action that freezes water movement between the nose and prey so that nothing interferes with subsequent vacuum suction.

Thus, living in a place where water is still or nearly so must enhance a seahorse’s ability to capture prey. Whether the horses I see now can survive in the open coast’s rougher waters beyond this season or will end up riding into the sunset (“Hi-yo, Silver, away!”) is to be seen. I do know a Pacific seahorse skeleton was recently found in the backyard of a home situated along the coast. It could it be that turbulent conditions pushed the seahorse into the beach where it was picked up, transported, and then dropped by a gull (seahorses are low-value prey as the bony body is nearly bereft of meat).

A seahorse is full of contradictions. It doesn't look like a fish but it is, and as the slowest swimming fish in the ocean, it doesn't seem it should be able to capture about the nimblest of Earth's critters but it does. Nature seems to have taken a left turn with the seahorse, an animal with a horse's head, a monkey's tail, a tortoise's lethargy, and a cheetah's agility.