A dive off Fly Point on his first holiday to Port Stephens in 1997 became a defining moment in David Harasti's life.

During his underwater exploration he spotted a White's Seahorse.

Because of that dive Mr Harasti, who is now the senior research scientist at the Taylors Beach Fisheries institute, moved to Port Stephens and has dedicated the past two decades of his life to studying the seahorse species.

But what sparked his love for marine science has turned into heartache for Mr Harasti as he has watched the White's Seahorse population in Port Stephens rapidly decline due to severe habitat loss, made worse by the March floods which decimated grasses, kelp and coral that housed the animals.

"When I went diving [in Nelson Bay] a month ago I came out of the water so disheartened. I've never seen such a grand scale of habitat loss ever, anywhere. It's like an underwater bulldozer had been through," he said.

"This is a site I have dived over 1000 times and I got lost because there was no reference points. It's all sand. Unfortunately, marine life don't do well in lots of fresh water and those floods in March had much more devastating effects underwater than what everyone realised."

Port Stephens used to be home to the largest White's Seahorse population but numbers have severely declined to the point that it was listed as an endangered species in 2020.

It is the second only seahorse in the world to be listed as endangered.

Mr Harasti has been studying the White's Seahorse since 2004. When he first started diving to observe the seahorses, he said he would find between 20 and 30 of the animals at the Pipeline, off Nelson Bay breakwall.

During his last two surveys at the site he has found only two. None can be found in the Seahorse Gardens off Nelson Bay Beach and very few at Fly Point and Little Beach.

"The White's Seahorse is known to live in habitats such as seagrass, sponges and soft corals," Mr Harasti said.

"In Port Stephens, the White's Seahorse occurrence is strongly linked to the presence of the endangered Cauliflower soft coral.

"The Cauliflower soft coral experienced dramatic declines in the estuary over the past decade and following the March floods, the abundance of the soft coral has declined by over 95 per cent across the entire estuary.

"Additionally, other important marine habitats for the seahorse also significantly declined following the March floods with some sites having 100 per cent loss in sponges, seagrass and kelp habitats.

"As a result of the habitat loss, recent surveys over the past few months has found that the numbers of White's Seahorse population in Port Stephens have declined.

"Sites where the seahorse used to be abundant, such as the popular dive site known as the Pipeline, now only has a few seahorses remaining. The other main site where the seahorse occurred, the Seahorse Gardens, the seahorses have all but disappeared.

"Without natural habitats for the White's seahorse to live on, the seahorses numbers have declined. If the habitats disappear, then the seahorses will decline as they require habitats to live on as they provide camouflage and attract prey for seahorses to feed on."

To assist in the recovery of the White's Seahorse in the wild, NSW DPI is involved in a conservation (breeding) recovery program with Sealife Sydney Aquarium, which has had positive results Mr Harasti said, and the installation of artificial habitats known as Seahorse Hotels.

Seahorse Hotels have previously been trialled in Port Stephens and were found to be effective at attracting seahorses back into sites where their numbers had previously declined.

Seahorse Hotels may be used in the future in the Port Stephens estuary to help the White's seahorse recover.

DPI is also assisting efforts to rehabilitate natural habitats.

Residents can assist efforts in restoring seahorse habitats at: seabnb.com.au.

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