Acidic Oceans Slowing Marine Fertilization
A recent study suggests that rising acidification of the ocean could reduce fertilization of marine invertebrates and might eventually wipe out colonies of sea urchins, lobsters, mussels and oysters.
Ocean acidification was known to be eating away at the shells of marine animals, but the new study has found that rising acidity hindered marine sperm from swimming to and fertilizing eggs in the ocean.
The report by Australian and Swedish scientists said climate change and the subsequent acidification of the world’s oceans would significantly reduce the successful fertilization of certain marine species by the year 2100.
"If you look at projected rates (of acidity) for the year 2100, we are finding a 25 percent reduction in fertilization," said lead-scientist Jane Williamson from Macquarie University.
"We were completely surprised because people had been looking at the effect of acidification on calcified structures of marine animals, but there was no evidence to suggest it was affecting non-calcified structures, like a sperm or an egg," she said.
Up to 30 percent of the world’s yearly emissions of carbon dioxide are absorbed by the surface of the ocean, causing carbon dioxide to form a weak acid that is gradually increasing the acidity of the oceans.
A link between increased ocean acidity and a reduction in swimming speed and motility of sea urchin sperm were found in a recent study of sea urchins around southeast Australia.
The researchers measured sperm swimming speed, sperm motility, fertilization success and larval developmental success in sea urchins in normal seawater with a pH 8.1 and also in water with a pH 7.7, which is projected to be the level of acidification by 2100.
In water with acidity at 7.7, the sperm swam much more slowly and began failing to meet the eggs, the study found.
The study published in "Current Biology" showed that fertilization fell by 25 percent and in almost 26 percent of cases where eggs were fertilized they did not survive to develop into larvae.
"It is widely believed that seawater is chemically well-buffered, but these results show that the acidification process already well underway may threaten the viability of many marine species," Williamson said.
Acidity levels of 7.7 were already occurring in patches of ocean off the west coast of the United States, she said.
Williamson also noted that when acidification rose to 7.4, which is projected by 2300, sea urchins failed to fertilize eggs and died.
"The paper has looked at the projected rates within the next 80 years, but we have actually looked at higher acidification values and we have had mortality of the animals," she said.
"What we have now is evidence that the world’s marine life is far more sensitive to ocean acidification than first suspected, and that means our oceans may be very different places in the not-too-distant future," Williamson said.
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