Transplanted kelp forests reviving the seafloor in Port Phillip Bay

Scott Breschkin stands on a boat in Victoria's Port Phillip Bay in his wetsuit, peering down below the surface at a seabed that has been stripped raw.

"These barren areas are quite striking — they really are barren," he says.

"There's not a lot growing there, they really are devoid of the typical healthy marine life that you'd expect to find."

The marine scientist from environmental nonprofit The Nature Conservancy explains that a dramatic rise in sea urchin numbers has decimated the golden kelp forests that should be growing here.

The seaweed species is vital to underwater life; kelp forests host a greater diversity of plants and animals than almost any other ocean community.

It's estimated there are now 130 million sea urchins in the water, and they've created what is known as "urchin barrens".

"We understand that they've affected about 60 per cent of all of the rocky reefs in Port Phillip Bay by over-grazing our native species," Mr Breschkin says.

In front of the research boat, he points to a series of dive flags floating in the water ahead.

They mark a site where two divers from the University of Melbourne are counting urchins as part of a project to try to restore the kelp forests, and Mr Breschkin swims out to see how it's going.

The highest count so far in this urchin barren is 20 of the spiny creatures in one square metre.

In a healthy kelp forest, there would be about 4 per square metre.

Why has the number of sea urchins exploded?

Climate change has caused devastation to kelp forests across the world — with rising sea temperatures impacting growing conditions, and allowing predators, such as sea urchins, to move into new areas.

But in Port Phillip Bay there have been some unique factors that have contributed to the rise in sea urchins.

It's estimated the number here has increased by between 250 and 420 per cent since the early 2000's.

One of the biggest factors has been the water quality in the bay improving.

For decades, wastewater discharge going into the bay pumped extra nutrients into the water.

Those nutrients allowed smaller seaweed to grow, creating easy food for the urchins — and so their number dramatically increased.

When the water going into the bay was cleaned up — all those urchins had to look for something else to eat and they started munching on the kelp.

"You change the balance of a natural system and then things get out of balance," Mr Breschkin says.

It coincided with the millennium drought, which also meant fewer nutrients going into the bay, because the runoffs dried up.

On top of that, predators such as lobsters that would eat the urchins have been overharvested, which also hasn't helped.

The plan to save the underwater forests

In a bid to undo "more than a decade worth of significant kelp loss", The Nature Conservancy has joined forces with the University of Melbourne, Deakin University and Parks Victoria to try to restore the kelp forests.

The innovative project has seen a culling of urchins at sites in the Jawbone Marine Sanctuary and the Ricketts Point Sanctuary within the bay, and the planting of 400,000 kelp, over two years.

It has involved growing baby kelp in a lab, and then transplanting it into the bay.

Diving in at one of the restoration sites, Mr Breschkin collects a rock from the sea floor and brings it to the surface, showing off a healthy kelp plant growing on it.

"When we plant these out, they're about 5mm in size, so they're pretty little, we can just see them with our eyes," he says, bobbing in the water and examining the kelp.

It was only planted about six months ago and has grown significantly.

"We see some pretty rapid growth, it's quite satisfying species to watch," Scott says, smiling.

The plant also shows signs of reproduction.

The team has been experimenting with a range of planting methods at the sites.

They've also been transplanting fully grown kelp from healthy forests in the bay into some barren areas and varying the level of ongoing urchin culling at different sites.

The lines of new kelp in the restoration sites are clearly taking to the reefs and growing. Nestled amongst one fresh patch of kelp is a stingray, and a school of fish swim overhead.

After a successful first two years, the Victorian government has given a $300,000 grant to continue the project for the next three years, and that money is being matched by the research organisations.

But Scott Breschkin says more money — from philanthropic organisations, companies or governments — will be needed long term.

"Now that we've demonstrated these methods, and we can show that we can have success with this restoration, we really want some big, bold commitments to help us really take this to scale," he says.

It's something he says is vital.

"Lots of fish and crabs and crustaceans and abalone really rely on those kelp forests to be there in order to survive," he says.

"They (also) provide a really good benefit in terms of being able to protect our shorelines, they improve our water quality — there's so many wonderful things that kelp forests do for us."

International kelp 'network' shares insights

The lessons and insights being learned here in Port Phillip Bay are being shared around the world.

Scott recently returned from a trip to Canada, where he worked with organisations there harvesting giant kelp grown in a farm off Vancouver Island and attaching them to rocks to be placed in restoration sites.

"It's a small network of people (around the world) and we're all very much connected," he explains.

"There's many parallels in terms of the situations people find themselves in — pressures from climate change, pressures from urchin overabundance.

"So together we can really solve these kinds of complex problems, with that kind of collaboration."

Closer to home, the information flows regularly across the Bass Strait, where researchers have been working to save Tasmania's giant kelp.

During a recent catch-up, Paul Tompkins, who leads the work for The Nature Conservancy in the state, said there were plenty of similarities across the sub-species.

"By him coming down here we're able to share all of that combined knowledge, experience and really synergise the way that we do our projects," he said.

Tasmania's giant kelp forests have declined by 95 per cent due to ocean warming but efforts to restore them have been bolstered by a significant grant.

The federal government is providing $3.5 million for a joint project, led by the University of Tasmania, to harvest sea urchins, replant kelp, and rebuild lobster numbers, as they are an urchin predator.

"We're just going to bigger and bigger scales, which is going to be really important to the recovery," Mr Tompkins said.