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Crystals from corals

Seen under a microscope, tiny crystals of aragonite (a form of the mineral calcium carbonate) are carefully organized into a “dissepimental sheet” in the skeleton of a Porites coral. Corals make dissepiments—a type of partitions—at the time of each full moon and use them like rungs on a ladder to support the weight of the coral polyps (individual coral animals) as they keep building new skeleton. WHOI scientist Anne Cohen studies the impact of climate changes, including ocean acidification, on the ability of corals and other marine calcifying organisms to build their calcium carbonate skeletons.
(Photo by Anne Cohen, Woods Hole Oceanographic Institution)