Sydney’s Massive Seaweed Decline Bad News For Fish And Crays

[Luringbream]

Sydney’s massive seaweed decline bad news for fish and crays

24 Jul 2007

The massive decline of one of two major habitat-forming seaweed species from Sydney’s shores has sparked deep concern and interest within NSW’s scientific community and alarm among fishermen.

Vital to supporting crayfish and abalone, as well as a vast number of small invertebrates eaten by fish, the once dominant ‘cray weed’ (Phyllospora comosa), as it is commonly called, appears to have gone missing in waters between Newport and Kurnell.

Dr Brendan Kelaher

The alarming discovery was made through research conducted by Dr Brendan Kelaher from UTS and Dr Melinda Coleman from the University of New South Wales.

Dr Kelaher said little study had been done by scientists into cray weed because it grows on exposed rocky areas of the coast where powerful waves make work difficult.

“Discovery of the loss of Phyllospora on Sydney’s shores has come as a great shock to marine scientists,” Dr Kelaher said. “The little bit of study that has been done on the species over past decades shows that it was abundant back in the 1940s and even 40 years ago, but serious decline was suspected during the 1970’s and 80’s.It would now seem that the species has gone altogether from around Sydney.”

According to Dr Kelaher the species is important not just as a habitat for juvenile crayfish, abalone and a host of other marine creatures, but when it dies and begins to rot into the sediment it begins an important food chain starting with bacteria and microscopic life and finishes with fish vital to our fishing industry.

“By comparing the volume and abundance of Phyllospora in healthy areas of the NSW coast we have calculated that up to 200,000 tonnes of this dominant seaweed is now missing from coastal habitats around Sydney,” he said.

“We suspect from laboratory studies that the loss has been caused largely by human sewage which was released over the years much closer to shore than it is now. This would have led to an overabundance of nutrients in the coastal waters. Although sewage outflow is now further out in deeper ocean, the damage seems to be permanent. – Phyllospora is not returning to waters off Sydney.”

Dr Kelaher said an irony of Phyllospora’s disappearance was that it should be growing in what are now some of NSW’s most protected coastal zones.

“These highly protected areas should be perfect for Phyllospora to recover in but as this is not happening we need to understand what we can do to help it return,” he said.

“With appropriate funding from the government and other groups we hope to investigate whether Phyllospora can be reintroduced from healthy stocks in other parts of the coast. This work has important implications for the long term health of our coasts and fisheries resources”