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Over the last two decades, a variety of natural and human-induced stresses have caused a decline in coral reef health around the globe. The success of coral reefs results directly from their ability to develop a structural framework of carbonate skeletal material and sediments through one of the more fundamental coral reef metabolic processes known as calcification. It is this 3-dimensional framework which shapes coastlines into a variety of reef habitats that support a diverse community of marine life.
Unhealthy reefs typically show a decrease in living coral and an increase in fleshy algae. Rates of calcification decrease, and more of the available carbon is used for growing fleshy tissues of the algae through photosynthesis than is used for producing calcium carbonate skeletons for the coral reef. Despite the significant role of reef metabolism, including calcification, photosynthesis, and respiration, in maintaining healthy coral reef ecosystems, there have been no known efforts to monitor metabolic function as an indication of reef health due, in part, to the difficulties in measuring reef metabolism.
Historically, reef metabolism has been measured by observing changes in the chemistry of seawater surrounding coral reefs that result from metabolic functions. This has been a difficult task because the complex shape of reefs causes water to move over reefs in an irregular manner, and scientists must be able to track a water mass as it moves across a reef so they can measure its water chemistry. Measurements of community-level reef metabolism have, therefore, been very limited.
Scientists of the U. S. Geological Survey’s (USGS) Coastal and Marine Geology Program have developed a method for trapping water over a coral reef community by placing a clear tent, 16’ long x 8’ wide x 4’ high, over corals on the seafloor. This device, known as the Submersible Habitat for Analyzing Reef Quality, or SHARQ, allows investigators to measure changes in the chemistry of the trapped water that result from metabolism of the portion of coral reef community located inside of the tent. It also allows them to change environmental conditions inside the tent to observe the response of the reef communities.
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