Fossils were used to determine the causes of previous extinctions. (Photo: Dr Maria del Carmen (K-le) Gomez Cabrera/ARC Centre of Excellence)
Sealife faces greatest risk of large-scale extinction
Thursday, August 23, 2012, 22:40 (GMT + 9)
Life in the world's oceans faces far greater change and risk of large-scale extinction than at any previous time in human history, a team of the world's leading marine scientists has warned.
The researchers from Australia, US, Canada, Germany, Panama, Norway and UK have compared events which drove massive extinctions of sea life in the past with what is observed to be taking place in the seas and oceans globally today.
Three of the five largest extinctions of the past 500 million years were associated with global warming and acidification of the oceans – trends which also apply today, the scientists say in a new article in the journal Trends in Ecology and Evolution.
Other extinctions were driven by loss of oxygen from seawaters, pollution, habitat loss and pressure from human hunting and fishing – or a combination of these factors.
|(Image: Dr Maria del Carmen (K-le) Gomez Cabrera/ARC Centre of Excellence)
"Currently, the Earth is again in a period of increased extinctions and extinction risks, this time mainly caused by human factors," the scientists stated.
While the data is harder to collect at sea than on land, the evidence points strongly to similar pressures now being felt by sea life as for land animals and plants.
The researchers conducted an extensive search of the historical and fossil records to establish the main causes of previous marine extinctions – and the risk of their recurring today.
"We wanted to understand what had driven past extinctions of sea life and see how much of those conditions prevailed today," says co-author Professor John Pandolfi, of the ARC Centre of Excellence for Coral Reef Studies and The University of Queensland, an authority on the fate of coral reefs in previous mass extinction events.
Marine extinction events vary greatly. In the 'Great Death' of the Permian 250 million years ago, for example, an estimated 95 per cent of marine species died out due to a combination of warming, acidification, loss of oxygen and habitat.
"We are seeing the signature of all those drivers today – plus the added drivers of human overexploitation and pollution from chemicals, plastics and nutrients," Pandolfi says.
"The fossil record tells us that sea life is very resilient – that it recovers after one of these huge setbacks. But also that it can take millions of years to do so."
Pandolfi adds: "The situation is not hopeless. In fact, we have seen clear evidence both from the past and the present that sea life can bounce back, given a chance to do so.
"In effect, it says we need to stop releasing the CO2 that drives these massive extinction events, curb the polluted and nutrient-rich runoff from the land that is causing ocean 'dead zones' manage our fisheries more sustainably and protect their habitat better.
"All these things are possible, but people need to understand why they are essential. That is the first step in taking effective action to prevent extinctions."
- Climate change will eradicate many marine species: study