Seaweed restoration. Photo: University of NSW

A barren stretch of Sydney underwater coastal landscape, most likely destroyed four decades ago when raw sewage was pumped into the sea, has been regenerated.

A team of researchers from the University of NSW, the Sydney Institute of Marine Science and the state Department of Primary Industries has transplanted crayweed onto two barren reef sites where it once grew abundantly.

They took seaweed from Palm Beach and Cronulla and transplanted it to Long Bay and Cape Banks. Their results are reported in the journal PLOS ONE.

“Seaweeds are the trees of the oceans, providing habitat structure, food and shelter for other marine organisms, such as crayfish and abalone,” says lead author Dr Alexandra Campbell from the UNSW Centre for Marine Bio-Innovation.

“The transplanted crayweed not only survived similarly to those in natural populations, but they also successfully reproduced. This creates the potential for a self-sustaining population at a place where this species has been missing for decades.”

The authors say the potential environmental and economic implications of losing these habitats would be comparable to the more highly publicised loss of Australia’s tropical coral reefs.

In 2008, researchers found that a 70 kilometre stretch of crayweed had vanished from the Sydney coast decades earlier, coinciding with a period known for high levels of sewage.

Water quality improved in the 1990s when better infrastructure pumped the sewage into the deeper ocean.

However, the 70 kilometre gap of depleted underwater forest between Palm Beach and Cronulla has never been able to recover naturally.

Now it looks like the habitat-forming crayweed could make a successful comeback in Sydney’s coastal waters.

“This is an environmental good news story,” says research supervisor Professor Peter Steinberg, Director of the Sydney Institute of Marine Science.

“This kind of restoration study has rarely been done in these seaweed-dominated habitats, but our results suggest that we may be able to assist in the recovery of underwater forests on Sydney’s reefs, potentially enhancing biodiversity and recreational fishing opportunities along our coastline.”

The project was funded partly by a grant from the NSW Recreational Fishing Trust.

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