By Susan Milius
By midcentury, growing acidification of the world’s oceans may undermine sexual reproduction in elkhorn coral badly enough to halve the supply of youngsters settling down to build reef.
Acidification, which happens as increasing levels of atmospheric carbon dioxide dissolve in the ocean and form acid, is expected to threaten established coral reefs worldwide in coming decades. In tests with seawater modified to reflect conditions expected later this century, sperm of the coral Acropora palmata successfully fertilized eggs 13 percent less often on average compared with sperm in today’s seawater, says Rebecca Albright of the University of Miami. In some of these tests using low sperm concentrations, which Albright suspects are more realistic, fertilization success dropped by as much as 64 percent.
Making that decline even more worrisome were tests indicating trouble with the next step in successful coral reproduction. With the same modified seawater, larvae from fertilizations that did succeed had more trouble settling successfully on a reef, Albright and her colleagues report in a paper to be posted online the week of November 8 in the Proceedings of the National Academy of Sciences. Settlements dropped by 45 percent.