The experiment found that in water with acidity at 7.7, the sperm swam slowly and began failing to meet the eggs.

Fertilisation fell by 25 per cent and in almost 26 per cent of cases where eggs were fertilised, they did not survive to develop into larvae, said the study published in Current Biology. “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.

“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.