DAVID WROE August 18, 2012
Towering trees facing extinction ... giant kelp, which faces depletion, in waters at Lagoon Bay, south-east Tasmania. Photo: J. Craig Sanderson
THEY are the mighty rainforests of the ocean, towering up to 25 metres from the seabed. And like many forests on land, the giant kelp jungles in the waters off south-east Australia are gravely threatened by climate change, scientists say.
In some areas off the east coast of Tasmania they have shrunk more than 95 per cent, according to CSIRO experts.
The threat is so serious the federal Environment Minister, Tony Burke, has listed the forests as endangered - the first time a marine ecological community has been given such protection under national environmental law.
''Giant kelp forests are being progressively lost due to a warming of the sea surface temperature caused by climate change, invasive species and changing land use and coastal activities that contribute to increased sedimentation and run-off and biodiversity loss,'' Mr Burke said .
The forests created a rich ecosystem by providing habitat for important species including black lip abalone and southern rock lobster, he said.
His remarks came as the CSIRO released a marine health snapshot that provided evidence for what scientists have long suspected: climate change has strengthened the East Australian Current which moves down the east coast, driving many marine species to seek colder waters further south.
The only remaining kelp forests are around south-east Tasmania, south-east South Australia and western Victoria.
Listing the forests as endangered won't help with climate change, but it means restrictions could be placed on activities that exacerbate the threat, such as overfishing and land uses that wash sediment into the sea.
Karen Gowlett-Holmes, a marine biologist with the CSIRO and co-owner of Eaglehawk dive centre on the east coast of Tasmania, said the destruction of the kelp forests was having ''a huge impact'' on marine ecology.
''If you can imagine what happens in an area where someone comes in and clearfells a rainforest, this is essentially what's happened,'' she said.
Dr Gowlett-Holmes said the minimum winter water temperatures off south-eastern Tasmania had risen 20 per cent over the past two decades. Giant kelp needs the cold winter waters to grow back after the natural cycle of destruction in sea storms.
Sea urchins, which devour the kelp, have reached pest proportions in the area, because they prefer warmer water and because their natural predator, rock lobsters, have been overfished.
''We can't change the fact the water is warming,'' Dr Gowlett-Holmes said. ''But … maybe if we can optimise the conditions under which it lives, we can maximise its chances.''