Seawater is becoming less alkaline as it absorbs ever more atmospheric carbon dioxide, levels of which are rising owing to fossil fuel use. As a result, seawater holds less calcium carbonate, so corals, molluscs and other creatures that use it to make their shells will struggle.
Corals were thought less at risk because they live in tropical seas rich in calcium carbonate, says Derek Manzello of the Atlantic Oceanographic and Meteorological Laboratories in Miami, Florida. But hurricanes could render them vulnerable.
Manzello and colleagues were monitoring two reefs off Florida when tropical storm Isaac swept through in August last year