Breeding seahorses to conserve their wild cousins

The courtship of Pacific seahorses begins with an awkward dance.

A close up of a Pacific seahorse (Hippocampus ingens) in the ¡Viva Baja! Life on the Edge special exhibit.

Over the course of several days, a female and a male seahorse will start to mimic each other’s movements. As their synchronization improves, the couple perfects a routine that involves circling each other, holding tails and swimming upward in unison.

“Their courtship dance involves going up the water column, so they need a few feet of vertical space,” says Jennifer O’Quin Anstey, senior aquarist at the Monterey Bay Aquarium. Her responsibilities include looking after a suitably tall holding tank, in a back room with soft light, behind the aquarium’s ¡Viva Baja! exhibit.

Nearby, smaller tanks are full of baby seahorses. They look like miniature versions of the adults—but begin their lives a dark hue. Their color alternates between black and yellow as they mature.

“People kept telling me how difficult it was to rear them, which only made me more determined to do it,” Jenn says.

Giving tanks

Wild Pacific seahorses may give birth to 1,500 offspring or more at a time, but perhaps as few as 1% of them survive to maturity. Jenn knew she could improve on that—but the right culturing tank would be key.

She tried out various designs, including cylindrical “kreisel” tanks made to hold other delicate animals. She tried black-out tanks and light-penetrating ones. Finally, she had some encouraging results with a 3.5-foot-tall, cylindrical black tank. It seems absurdly large for seahorses so small, but it worked the best.

Four broods in, she now has about 180 Pacific seahorses in the lab. “It was getting better with each batch,” she says. “I was euphoric.”

Of dozens of known seahorse species, Pacific seahorses (Hippocampus ingens) are among the largest, with fully-grown adults approaching a foot in length. Yet, they give birth to some of the smallest seahorse babies: Newborns are barely the size of a grain of rice, and they can be picky eaters.

An aquarist feeds Pacific seahorse fry behind the scenes at Monterey Bay Aquarium.

Seahorse baby food

Our Pacific seahorses dine on very tiny crustaceans: copepods, brine shrimp and mysid shrimp. Figuring out how to provide our seahorses with enough of the appropriate food source at each developmental stage is crucial for successful culturing.

To ensure a stable supply of the right feed at the right time, Jenn and her colleagues raise several species of copepods, which are especially nutritious for baby seahorses (or “fry”). They also feed probiotics to brine shrimp, which packs them with more nutritional punch. Once the fry reach two to three months of age, they transition to eating mostly mysid shrimp, which are a lot less work to raise behind the scenes.

“The first two months are the hardest,” Jenn says. “After that, you start to breathe easier.”

Raising both seahorses and their food is more than a full-time job. Jenn and three other aquarists—Sarah Halbrend, Kacey Kurimura and Alan Young—team up to provide the necessary seven-day-a-week care.

Seahorse culturing is about more than the strange cuteness of baby seahorses. Our team’s ambition is to ensure a healthy and self-sustaining Pacific seahorse collection for our ¡Viva Baja! special exhibition without relying on additional wild collection. Our success will allow other public aquariums to exhibit this species, and share its conservation story.

Threats to wild Pacific seahorses

Pacific seahorses range from the coast of Southern California all the way to South America. The International Union for Conservation of Nature and Natural Resources lists them as a vulnerable species.

Aquarist Jenn Anstey raises Pacific seahorses (Hippocampus ingens) behind the scenes of the Aquarium’s “¡Viva Baja! Life on the Edge” special exhibit.

Jenn describes the threats to Pacific seahorses as a mix of coastal development, incidental capture and targeted catch. They’re collected and sold as curios, and used in traditional medicine, as well as for the live aquarium trade.

Part of the reason we’re working to breed Pacific seahorses in-house is so that fewer are taken from the wild, according to Jonelle Verdugo, curator of fishes and invertebrates at the Aquarium.

“This species in particular is not very commonly displayed in aquariums, and isn’t as readily available,” Jonelle says. “Wild capture is something that we would really like to avoid.”

Breeding Pacific seahorse populations in captivity, however, can introduce the problem of dwindling genetic diversity. Without new wild seahorses bringing different genes to the pool, subsequent generations may face health issues. This is another challenge we’re addressing, with help from aquarium colleagues in Los Angeles County.

Swapping seahorse notes

In 2015, ocean researchers trawling in Southern California waters happened to catch two pregnant male seahorses, and donated both to Cabrillo Marine Aquarium in San Pedro. (Seahorses are part of that rare group of animals in which males carry their young to term.) On the drive to Cabrillo, one of the seahorses gave birth in a bucket.

It was a stroke of luck, according to Cabrillo Culture Aquarist Cody Larsen, because he’d been thinking about how to get Cabrillo’s seahorse breeding program in gear. Once the young Pacific seahorses were several months old, Cabrillo gave five of them to Monterey Bay Aquarium’s team, adding to our existing broodstock. Since then, Cody and Jenn have kept in touch to fine-tune their culturing protocols.

A Pacific seahorse on exhibit at the Monterey Bay Aquarium.

“I was very excited to hear from Jenn that she started having success rearing Pacific seahorses,” Cody says. “They’ve proven to be a difficult species to raise. To have a shared success makes me feel hopeful, because for a while, they had disappeared from almost all aquarium collections.”

As more of our young seahorses reach maturity, around four or five months of age, Jenn intends to share some of them with other aquariums. That will add the necessary new genes to existing captive broodstocks elsewhere.

“They’re going to go like hotcakes!” she says.

The work of Monterey Bay Aquarium and Cabrillo Marine Aquarium may make this impressive seahorse species more widely and sustainably available to other public aquariums in the U.S. That, in turn, will help reach more people with important stories about seahorse conservation.

“It’ll increase the genetic diversity of the captive-reared populations at other aquariums, while helping wild populations,” Jenn says. “It’s nice to know I can help spread the love.”

-Daniel Potter