A Goldring Surgeon fish
Waters off the eastern Australian coast are among the fastest warming in the world, bringing significant changes to marine eco-systems, scientists say.
As reported in the latest Intergovernmental Panel on Climate (IPCC) report released on Monday, the East Australian current has advanced about 350 kilometres towards the South Pole in the past 60 years. By comparison, currents off north-eastern Australia have extended 200km south, while those off north-western WA about 100km.
"Under all (greenhouse gas) emissions scenarios, pelagic fishes such as sharks, tuna and billfish are projected to move further south on the east and west coasts," according to the IPCC report on the impacts of climate change.
While some species can adapt by migrating to cool waters, eventually they run out of continental shelf.
"At some point they can't move further south, there's no land," said Adriana Verges, a marine ecologist at the University of NSW. "It's like they are falling off a cliff edge".
Dr Verges is a co-author of new paper on changing habitats in a warming ocean, led by UNSW colleague Alex Sen Gupta.
The report, published in Deep-Sea Research II, found poleward shifts in marine species for almost all regions, with summer shifts likely to be considerably faster than in winter – contrary to experience on land.
The observed poleward movement in marine species is about 10 times the range of land-based creatures, Dr Verges said. That's likely to be the result of marine environments typically being more stable than terrestrial ones, so that a small change has an amplified impact has species capacity to perform aerobically.
For eastern Australia, temperatures are as much as 3 degrees warmer than in the past, which means the arrival of new species with unpredictable impacts.
Damsel and surgeon fish, for instance, are appearing in Sydney Harbour, while spiny sea-urchins are grazing their way south with devastating effects on kelp forests off the Tasmanian coast.
So-called foundation species, the kelp forests are home and food for commercially fished species such as abalone and lobster. The sea-urchins over-graze, turning the kelp into barren ground and then "you lose everything else", Dr Verges said.
Kelp forests are also found off the northern NSW coast but these species too are making way, in some places, for coral reefs.
Dr Sen Gupta and his team used climate models to map how species’ habitats will change as the ocean warms.
"We find that under a business as usual emissions scenario, migrations will accelerate about seven times; from about 10km per decade in the 20th century to 70km/decade in the 21st century," he said. "We also show that because summer ocean temperatures warm faster than winter ocean temperatures the area of species habitats will tend to shrink over time."
The researchers also found the migrations are unlikely to happen smoothly. Instead species are more likely to jump from one location to another in fits and starts, Dr Sen Gupta said.