"Slow sperm ... now that’s a problem,” said Jonathan Havenhand, his British accent compounding the gravity of the message. “That means fewer fertilized eggs, fewer babies and smaller populations.” We were sharing a hilly cab ride along the glistening northern coast of Spain to attend an international symposium about the effects of climate change and excess atmospheric carbon dioxide on the world’s oceans. As researchers, we were concerned about the underappreciated effects of changing ocean chemistry on the cells, tissues and organs of marine species. In laboratory experiments at the University of Gothenburg in Sweden, Havenhand had demonstrated that such changes could seriously impede the most fundamental strategy of survival: sex.
Ocean acidification—a result of too much carbon dioxide reacting with seawater to form carbonic acid—has been dubbed “the other CO2 problem.” As the water becomes more acidic, corals and animals such as clams and mussels have trouble building their skeletons and shells. But even more sinister, the acidity can interfere with basic bodily functions for all marine animals, shelled or not. By disrupting processes as fundamental as growth and reproduction, ocean acidification threatens the animals’ health and even the survival of species. Time is running out to limit acidification before it irreparably harms the food chain on which the world’s oceans—and people—depend.