Crayweed makes a comeback on Sydney coast

What do walkmans, floppy disks, VCRs and crayweed have in common?

They all thrived in the 1970s before eventually disappearing.

But now one of them has been brought back to life on the Sydney coastline by marine ecologists.

The seaweed species crayweed - Phyllospora comosa - used to grow in abundance on shallow rocky reefs on Sydney's shores until the late 1970s when it vanished due to high levels of sewage.

Despite improved water quality and better management of sewage in the 1990s, the 70km stretch of coastline between Palm Beach and Cronulla where the algae once grew didn't recover.

More than 40 years later, a team of researchers from the University of NSW, the Sydney Institute of Marine Science and the NSW Department of Primary Industries have successfully restored the once-thriving seaweed along Long Bay and Cape Banks.

They did this by taking algae from Palm Beach and Cronulla and transplanting it onto the two barren reef sites.

The transplanted crayweed not only survived, but reproduced, which scientists say provides valuable insights for restoring similar macroalgae marine ecosystems in Australia and globally.

Alexandra Campbell from the UNSW Centre for Marine Bio-Innovation said seaweed habitats play an important role in underwater biodiversity.

"Seaweeds are the 'trees' of the oceans, providing habitat structure, food and shelter for other marine organisms, such as crayfish and abalone," she said.

Losing these habitats would be comparable to the loss of Australia's tropical coral reefs.

The Sydney Institute of Marine Science believes this study will give scientists more tools to combat the degradation caused by humans and ocean warming.

"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," Professor Peter Steinberg said in a statement.