On our second afternoon at Woleai, I had the opportunity to deploy my drifter. I went out to the reef in one of the small boats that we use to move from the big ship, anchored in deep water, to the shallow reef area, near the shore.
To begin, I looked around to observe the water movement, and I jumped in the water to feel which way the current was going. Once I knew which end was upstream, I went to the upstream end of the reef and dropped the drifter in the water. At this point, I sampled the water and I left the drifter to float along with the water across the reef. The drifter tracked where the water was going. After the water (and drifter) crossed the reef, I sampled it again.
While the water was passing over the reef the water was interacting with the coral community. As the coral were growing, they were extracting the chemical building blocks for their skeletons directly out of the water. When I measure the chemistry before and after the water interacts with the coral reef, I can determine how much they grew during that time. This means that I can calculate how fast the community is growing, collectively. The community is comprised of corals that generate carbonate (limestone) skeletons, coralline algae that also deposit carbonate mineral, sand which is dissolving carbonate back into the water, and a multitude of organisms with carbonate shells. Measuring the net growth of this community is one way to evaluate the health of a community and to assess its sensitivity to changes in the environment.