‘Tis the season for seahorse sex

It’s January, and seahorses in the southern hemisphere are full swing into some summer lovin’.  And if you’re out cruising the seagrass beds off Australia’s south coast, you might get lucky too, and witness the remarkable act of a female impregnating a male. Seahorses turn the tables on sexual roles.

And while their cryptic coloration makes courting seahorses difficult to see, especially observant divers—like the two researchers who filmed the footage below—might catch a glimpse of the extraordinary aftermath of seahorse sex: a seahorse dad giving birth in the wild:

Yes. That is a pregnant male giving birth to about 150 to 200 baby seahorses that he’s been carrying around, nourishing and protecting, in his belly pouch for about three weeks. During this entire time, he hasn’t had any sex.  For these expectant fathers, pregnancy brings with it some strict celibacy.

Here’s why. During “intercourse”, a female seahorse deposits eggs via an oviposter (which looks like tiny phallus protruding from where her belly button would be).  This stubby tube extends from her belly, pushed outward by the swelling of eggs inside her, and enters into the male’s open pouch.

In several seahorse species, a horny male shows he is ready for action by flexing his body, pulling tail up towards nose and then straightening out. This serves to fill his pouch with water, ballooning it outwards and showing off the big, gaping cavern where he will nurture the young. (The side effect of this vigorous folding action is that his stretched opening looks an awful lot like a natural form reminiscent of a Georgia O’Keefe).

Male Hippocampus subelongatus, with prominent belly pouch ready to burst with babies. Photographed by Tammy Gibbs. Tammygibbsphotography.wordpress.com.

Male Hippocampus subelongatus, with prominent belly pouch ready to burst with babies. Photographed by Tammy Gibbs. Tammygibbsphotography.wordpress.com.

Females are likely turned on by the site of this enormous chamber, and will commence consummation.

After the female has deposited her eggs into his pouch, the male then seals it shut, releasing sperm into the chamber to fertilize the eggs. His pouch then fills with nourishing fluids to bathe the embryos and must remain sealed to prevent seawater—which is fatal to developing young—from getting in. Thus, the three-week dry spell for seahorse action.

But just because there is no sex, doesn’t mean they don’t flirt. In fact, for White’s seahorse (Hippocampus whitei)—the species caught on film above—a pair of lovers continues to meet and greet each other every day throughout the pregnancy.

Though flirtatious, this formal courtship is straight out of a Jane Austen novel, complete  with proper etiquette.

A male arrives at a designated “greeting” spot at dawn; the female then makes her entrance and quickly swims to the male while the two “blush” colors at one another. Each seahorse then grasps a blade of grass with their delicate curving tails, and begins to circle around in the same direction, the male making the larger outer circle around the female. Periodically, they release their grasp and swim side-by-side, tails often entwined, along the seagrass meadow, like two lovers out for a morning stroll. Then, they repeat.

This happens for several rounds, and then the two part, returning home (like proper lads and ladies), until the next morning.

A pair of White’s seahorses having their morning dance. Photo via ARKIVE.org (c) Georgette Douwma

A pair of White’s seahorses having their morning dance. Photo via ARKIVE.org (c) Georgette Douwma

Staying with the same partner is, well, rather aberrant behavior for any species.  Nowadays, genetic tests have shown that only a handful of species are really monogamous. But White’s seahorses are one of them (at least for a season), with males and females staying true, one sexual bout after the other from October to about April.

One of the potential reasons for this is that having a dedicated partner helps coordinate some perfectly timed sex. For males, they need a female with ripe eggs, ready to go, within a few hours after giving birth in order to fully maximize the reproductive season. Females, on the other hand, have a limited window of only a few days to hold onto their eggs once they have hydrated them—if a male doesn’t show, she has to dump the whole batch.That’s a huge energetic waste on her end.

By staying closely bonded, females can regulate egg development to correspond to when their male will be ready to receive another round. The male ensures he has a female in synch with his birth schedule; the female gets a male who shows up on time.

Only when the male has just given birth will he signal—via the vigorous body flexing—that he is ready to take things beyond the morning dance ritual. Courting the female may take several minutes or even hours, depending. Should he be successful, however, he will receive a pouchful of eggs…and commence his journey through pregnancy once again.

White’s seahorse female transferring eggs to male. Photo via ARKIVE.org, (c) Rudie Kuiter/ gettyimages.com.

White’s seahorse female transferring eggs to male. Photo via ARKIVE.org, (c) Rudie Kuiter/ gettyimages.com.

As soon as those babies are out the door, the male is ready to go again—pretty impressive for someone who has just given live birth to dozens of young. With a mating season of only about 6 months, pregnancies are stacked back to back—an endeavor made easier by the fact that his mate is patiently waiting for him back at lovers lane.

The next time you gaze out across the shimmering sea, consider this: somewhere out there, right at that very moment, you can bet there is some creative (if not kinky) sex going on.

Throughout 2016, Sex in the Sea will bring you updates about who is getting down to business each month. A calendar to accompany the stories is in the works, but for now, check back regularly to stay on top of the hanky-panky happening beneath the waves as we circle round the sun.