Diving into Hawai‘i's reef history

by Hannah Whitaker

The physical and chemical properties of a coral’s skeleton can tell us a lot about past ocean conditions; some coral species maintain environmental records that go back hundreds of years. The Sclerochronology lab has a collection of coral cores from all over the world, and this past summer, we expanded our library to include 10 new specimens from here on ‘Oahu!

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​Under a permit from the Division of Aquatic Resources, our team of divers (Dr. Tom DeCarlo and graduate students Hannah Whitaker and Jess Hankins) identified and cored colonies of Porites lobata in Waimanalo Bay over the course of five dives. Lobe coral is one of three dominant coral species on the island, and its massive growth form and long-lived nature make it an excellent candidate for sclerochronology.

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​The drill we use is pneumatic—powered by pressurized air—and produces cores that are 5 cm in diameter, about as big around as a water bottle. Once the core is removed, we plug the hole with cement and marine epoxy to keep bioeroders out and so that the surrounding coral has a new surface over which to grow back. Within a few months, it’s like we were never there.

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Back on land, we rinse, soak, sonicate (using a high-frequency sound bath to remove debris), oven-dry, and carefully wrap each core so they can be stored for later analysis. Our longest core from Waimanalo likely dates back over a hundred years, and the lab is excited to see what history is written in these growth bands.

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