Sydney harbours a surprise

Despite heavy human impacts -- including record-breaking toxic sediments and rising nutrient pollution -- Sydney Harbour’s marine life is richer than in more pristine marine parks nearby, new studies have found.

Recent biological surveys of NSW estuaries revealed that larval fish are more abundant and diverse in heavily modified harbours and bays. As well, adult fish in Sydney Harbour, such as flounder and snapper, are often larger than in less-modified estuaries.

Sydney scored best in comparison with Port Hacking, Jervis Bay and Bateman’s Bay, the latter two of which feature significant marine parks.

"It’s a wonderful paradox," says Associate Professor Emma Johnston, who co-led a series of studies by the UNSW Ecology and Toxicology Group, in conjunction with Dr Melinda Coleman, a Senior Research Scientist at NSW Fisheries.

"This pattern extended to other communities of marine life and we saw more species richness and abundance of organisms living in the sediments, particularly bristle worms in Sydney Harbour.

"This apparently good news for Sydney Harbour is partly attributable to the reduced input of heavily toxic contaminants that has occurred since the EPA began regulating pollution in the mid-'70s.

"Another explanation is the ongoing input of nutrients from diffuse sources such as stormwater run-off and sewage leaks.  It looks like they have given the whole system a kick -- a bit like a fertiliser effect.

"Up to a point, the input of nutrients will increase productivity, but too many nutrients leads to algal blooms and fish kills. Determining when we might breach the threshold nutrient concentration is an important research question for Sydney Harbour."

The researchers used baited underwater cameras to film and count fish. They also used nets to sample and weigh adult fish, as well as sampling invertebrate creatures in sediments.

"The whole food chain turned out to be more productive in Sydney Harbour," says Dr Coleman. "It is a naturally productive waterway anyway, but humans have added all those extra nutrients and all those extra structures for animals to inhabit -- such as wharves, jetties, sea-walls and bridge pilings."

Professor Johnston notes that the harbour’s saving grace is that it is well-flushed by fresh seawater, especially in its lower reaches

“We need to remember that commercial fishing was banned in the harbour in 2006, not least because we still have world-record levels of toxic contamination in sediments: eating fish caught anywhere west of Sydney Harbour Bridge is not recommended."

Photos courtesy of Fishabout Tours