Seaweed advances south to extinction
Swathes of Australia's seaweed are shifting south to escape warming oceans and many risk becoming extinct, a new study has found.
Marine ecologist Dr Thomas Wernberg, of the University of Western Australia, and colleagues, reported their findings today in Current Biology.
"Temperate species are moving to cooler environments," Dr Wernberg said.
"In Australia there are no cooler environments beyond the south coast, so if they are pushed to go beyond that they basically go extinct."
While a lot of attention has been paid to the impact of climate change on corals, Dr Wernberg says the impact on seaweed has been neglected.
He says while seaweeds might seem mundane, they are an important habitat and food resource for underwater animals and plants.
"Just as trees in the forest provide living space for birds and other animals, so do the seaweeds in the oceans. There's a large amount of biodiversity associated with seaweeds," Dr Wernberg said.
He says while coral reefs tend to be restricted to tropical waters, seaweeds are more widespread, so any impacts on them could have a broader cascading effect on marine ecosystems.
Drawing on electronic records of seaweed from Australia's Virtual Herbarium, Dr Wernberg and colleagues looked at how seaweed communities comprising up to 300 species had changed over time.
They also compared the distribution of 52 species of seaweed along the east and west coasts of Australia during the period 1940 to 1960, with seaweed distribution during the period 1990 to 2009.
Dr Wernberg says between the two 20-year time periods, the ocean warmed by a couple of degrees in south-east Australia and by a degree on the west coast.
"What we saw is that the seaweed communities migrated south towards the cooler environments," he said.
Although this was the case on both the east and west coasts, the researchers found that seaweeds moved further south on the east coast where the warming had been greater.
On the east coast, seaweed species had moved around 200 kilometres south, while on the west coast they had moved about 50 kilometres, Dr Wernberg said.
"If this rate of shift continues, a relatively large number of species could go extinct," he said.
Dr Wernberg says once a species gets to the south coast, they will not be able to move any further south and if temperatures continue to rise, they will run out of alternative habitat to move to.
"So if they can't exist under the new conditions they literally fall off the continent," he said.
Based on the known temperature ranges of various species of seaweed, he says a "back of the envelope type calculation" estimates as much as 25 per cent of temperate species in Australia could be extinct by 2070.
Interestingly, Dr Wernberg and colleagues found a few species of seaweed, including Caulocystis uvifera, actually moved some tens of kilometres north instead of south with warming oceans.
Dr Wernberg says this could be because for these species, competition is more important than climate in determining their distribution.
He said it may be they move north as competitors move south.