How ‘seahorse hotels’ are reviving an endangered species

A seahorse species found only on Australia’s east coast is at the heart of a quiet conservation project in Sydney Harbor.

White’s seahorse is shy, delicate, and now one of the only seahorse species in the world officially listed as endangered. One major reason? Its home is disappearing.

A disappearing seagrass meadow

Researchers from UNSW Sydney have found that one of the seahorse’s key habitats, a native seagrass called Posidonia australis, has nearly vanished from Sydney’s coastline.

Urban expansion, pollution, dredging, and boat traffic have all played a role in wiping out these once-extensive meadows over the past 50 years.

“As the seagrass meadows disappear, so too do the species that depend on them,” said Professor Adriana Vergés. She’s part of the Greener Pastures conservation project, and a lead figure in Operation Posidonia and Project Restore – both focused on bringing life back to the harbor.

“There is minimal Posidonia remaining in Sydney Harbor,” noted Professor Vergés. “Historically, these meadows were extensive but coastal development and physical disturbances have wiped much of them out.”

“We predict Posidonia will be locally extinct from Sydney Harbor within the next couple of decades unless we do something about it.”

These meadows aren’t just pretty patches of greenery. They play a key role in keeping the shoreline stable, stopping erosion, storing carbon, and giving marine species places to feed and breed.

Why habitat matters for seahorses

Seahorses don’t swim like most fish. They float upright and use their prehensile tails to grip seagrass leaves, coral, or sponges. It’s how they stay put when the currents get strong.

“With the Greener Pastures project, we are aiming to tackle one of the root causes of the decline in White’s seahorse populations, which is the loss of habitat,” said Professor Vergés. “We can breed and release them, but unless we restore their homes, their populations will keep falling.”

That message is echoed by Mitchell Brennan, program manager of the Sydney Seahorse Project and a Ph.D. candidate at the University of Technology Sydney.

“To hold on to that habitat is critically important,” said Brennan. “Seahorses rely on highly complex habitats like seagrass meadows to camouflage, anchor and feed.”

Inspiration for seahorse hotels

However, rebuilding a seagrass meadow isn’t something you can do overnight. While the grass grows, scientists have found a clever way to support the seahorses: hotels.

The idea was first introduced by Dr. David Harasti from the NSW Department of Primary Industries and Regional Development.

He was inspired by old crab traps that were covered in marine life and designed steel mesh cages – about a meter wide – to mimic the complex tangle of a natural underwater habitat.

“When left on the seafloor these bespoke hotels soon become encrusted with sponges, corals and algae,” explained Dr. Harasti.

Safe zones for seahorses

Each cage turns into a safe zone for seahorses. The encrusted material offers camouflage, food, and places to hold onto. Soon, the seahorses start showing up. According to Dr. Harasti, the seahorses move in within three to six months.

At Cobblers Beach, a major site for the project, 15 seahorse hotels were placed next to existing patches of Posidonia in late 2023. Additional seagrass shoots were transplanted shortly after.

Early surveys showed up to eight seahorses. By 2024, there were 12 – including juveniles likely born on-site.

When dads give birth

Seahorses are unusual in more ways than one. One of the most fascinating things about them? It’s the males who give birth.

“We’ve seen multiple pregnant males and partners on the seahorse hotels in the past six months,” said Brennan. “With some of these juveniles being sighted, hopefully the population starts to grow and become stronger and more self-sustaining.”

The hotels may also be helping the newly planted Posidonia itself. Their structure offers protection from waves and shifting sand, giving the delicate grass a better chance to take hold. And as the habitat improves, other species are returning too.

“In areas where we’ve replanted seagrass, we’re already seeing more fish – snapper, flathead, bream and even pajama squid,” said Brennan. “It’s about restoring the function of the whole system.”

The role of community engagement

While the science behind Greener Pastures is solid, its heart comes from community involvement.

“This all started when Operation Posidonia received a grant from the Environmental Trust and support from Mosman Council,” said Professor Vergés.

“The local community is incredibly engaged. They’re not just helping us plant seagrass – they’re also learning why it matters and sharing this information with their friends and neighbors.”

From the early days of the project in Port Stephens, volunteers have helped collect thousands of loose Posidonia shoots from storm events. Those shoots are then replanted into damaged meadows.

Connecting people with ecosystems

“Hands-on restoration helps people connect with ecosystems they might never have known about,” said Professor Vergés.

“When people become part of the process, they gain a sense of ownership – that’s where real stewardship begins. You can’t protect what you don’t know exists.”

Her goal for the next decade is simple: recovery – for both the seagrass meadows and the seahorses that depend on them.

“I’d like to see a growing population of White’s seahorse occupying this habitat – both of them recovering together.”

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