Pollution killing off vital Moreton Bay mangroves

Brian Williams couriermail 20 Jun 09;

SCIENTISTS fear pollution may have killed off up to 6000ha of mangroves in Moreton Bay _ trees vital in maintaining fish and healthy foreshore areas.

One theory was that cancerous pollution or chemical spraying for mosquitoes was killing tiny fauna such as crabs, molluscs and worms that lived in the soil around the trees. Mangroves need the creatures to aerate the soil and transfer nutrients.

The loss over five years equates to as much as 20 per cent of the bay's mangroves.

Stark forests of dead mangroves range from North Stradbroke Island in the south to Redcliffe in the north and the city's edge at the Port of Brisbane.

As trees die, the soil sinks around them, causing foul ponds in which nothing regenerates.

University of Queensland wetlands specialist Norm Duke said yesterday it was first thought drought was the issue but it appeared the cause was farmore complex.

One theory was that cancerous pollution or chemical spraying for mosquitoes was killing tiny fauna such as crabs, molluscs and worms that lived in the soil around the trees. Mangroves need the creatures to aerate the soil and transfer nutrients.

"As a result of this change, we might be getting faster breakdown of root material," Dr Duke said.

"There are lots of air spaces around the roots and these are collapsing. Dieback is normal but what is abnormal are these ponds forming. We're getting sediments sinking 20cm to 30cm. Affected areas have expanded rapidly, in some cases from less than 1m wide to many now in the last year that exceed 1km or morein diameter."

Primary Industries Minister Tim Mulherin said the die-back appeared to be caused by a mix of natural and man-induced events. DPI experts did not believe it was related to mosquito spraying, as the insecticide did not affect mangroves.

"We're working with the Port of Brisbane to identify causes and come up with response plans," he said. "Areas of concern include Whyte Island and Cobby Cobby Island. We are promoting natural colonisation where possible and looking at alternative solutions such as improving drainage."

But Dr Duke said mosquito spray could not be discounted.

"After all, you use it to kill things," he said.

Wildlife Preservation Society president Simon Baltais urged the Government to boost research.

"The sad fact is you can't manage what you don't understand and the Government doesn't have a clue about what is going on," he said.

"It rabbits on about how healthy the bay is while up to 20 per cent of mangroves are gone. Without mangroves you don't have fisheries. If we've lost about 15 per cent of mangroves then you'll find we've lost about 15 per cent of fish resources.

"There is no issue more important to commercial fisheries, recreational fishers and all the boating and bait industries. Without fish, they have nothing."

Mangroves nurture 75 per cent of Queensland's commercial and amateur fish catch and are known as "coastal kidneys" for the job they do in filtering run-off and protecting coral reefs.

Dr Duke is setting up coastal MangroveWatch organisations which are aimed at raising awareness and understanding changes taking place.

He said dieback had occurred at other places but in those cases, mangrove marshes had been replaced with other natural wetland systems such as saltpans and saltmarsh vegetation.

"Mangroves not only support fisheries but protect coastal margins from things such as storm surges and erosion," Dr Duke said.

He is seeking evidence of changes to work out where and when sinkage began.