I don't see-weed: the rehabilitation of Sydney's underwater forests

Decades ago, it was a common sight to see brown seaweed washed ashore along Sydney’s Manly Beach. Nowadays, the same sight has been replaced by masses of green seaweed.

This seemingly innocuous change in scenery actually embodies a complicated story taking place beneath the ocean’s surface. The brown seaweed species Phyllospora comosa, commonly known as crayweed, once grew in abundance along Sydney’s rocky shores until the 80s when Sydney’s poor sewage system took its toll on crayweed populations.

The sewage wiped out 70 kilometres of dense, diverse underwater forests.

Although Sydney’s water is at its cleanest since then, crayweed has been unable to re-establish itself, having been crowded out by the green seaweed, Caulerpa filiformis.

But a joint venture between the Sydney Institute of Marine Science (SIMS) and the University of New South Wales (UNSW) is showing signs of success re-establishing crayweed forests between Palm Beach and Cronulla.

The crayweed restoration project, led by scientists Dr. Ezequiel Marzinelli, Dr. Alexandra Campbell, and Prof. Peter Steinberg, collects adult crayweed from outside of the Sydney metropolitan area where it is still naturally occurring, healthy, and prolific. It is tied to metal grids, and divers then transplant these grids to the shallow, rocky shores of the Sydney metropolitan area.

The ecologists carried out the restoration project’s first transplants in 2011 and results have so far surpassed expectations.

“Not only did the crayweed survive, they actually reproduced at rates higher than what we’ve seen in existing natural populations,” says Dr Marzinelli.

“We’re even seeing second and third generation crayweed. Our initial transplants are grandparents.”

The crayweed has even begun to spread out beyond their metal patches to form what looks like the beginning of the return of the forests.

“We’ve found crayweed patches 10 to 100 metres from our initial grids,” says Dr Campbell.

“It’s been very encouraging and suggests that these restoration projects, even at a very small scale, can potentially produce cascading effects.”

Forming a forest

While the green Caulerpa and the brown crayweed are both considered to be habitat-forming seaweeds, scientists have yet to see any significant ecological benefits of Caulerpa’s spread.

“Though Caulerpa is a native species, it is a very good colonizer — as soon as crayweed populations declined, Caulerpa was able to fill in its space,” says Dr Paul Gribben, Associate Professor of Invasion Ecology at the University of New South Wales.

“Caulerpa provides a less diverse community. In fact, it is highly chemically defendant so many creatures can’t even eat it.”

Crayweed, on the other hand, has been shown to support a significantly higher number of creatures, such as crayfish, oysters, and abalone.

In fact, crayweed supports, on average, more than 20 times the number of abalone than other habitat-forming seaweed.

Scaling up

While it is still too soon to see if the transplants have altered the marine biodiversity of the Sydney area, the project is moving in full swing to restore crayweed forests.

“We are now working on scaling the project and enhancing the crayweed babies until [crayweed reproduction] becomes a fully self-sustaining process,” says Dr Marzinelli.

Despite the project’s early wins, the lead scientists are faced with the immediate challenge of raising support and awareness to scale restoration.

Some of the project’s initial funding came from the Recreational Fishing Trust and the Environmental Trust, which are both organisations that value the ecological and economical importance of crayweed forests. However, funding from the trusts is not enough. The crayweed restoration project will also be launching a crowdfunding campaign in the coming months to raise money for expansion.

“Our project is actually not that expensive,” says Dr Marzinelli. “Including some initial mess-ups that we experienced, it cost us about $30,000 dollars a hectare. Putting that in context, restoring coral reefs costs anywhere between $13,000 and $100 million dollars a hectare.”

“If we were able to turn the restoration project into a community-based project, it would be way cheaper. I reckon it could be cut down to $10,000 a hectare.”

However many Sydney residents are unaware of crayweed and its importance in sustaining other creatures.

“You get a lot of media attention on the Great Barrier Reef, which is fair enough because it supports a lot of biodiversity,” says Dr Marzinelli. “But when you look further south, the equivalent to coral reefs are these seaweed forests, which are not only found in Sydney, but are also found on the coastlines of California, South America, and South Africa.”

Nige Coombes, a recreational diver and a volunteer with the project never realised anything was amiss from his dives around Sydney.

“I haven’t been diving for too long — for only about 6 years — so for me, the ecology of the Sydney area just didn’t include [crayweed],” he says.

“Before volunteering, I’ve never seen it while diving so I never thought of the possibility of there being something missing. I’ve got a mate from Manly that’s been diving for decades and he said he used to see crayweed all of the time.”

 

View original article at: I don’t see-weed: the rehabilitation of Sydney’s underwater forests

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