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U.S. Department of the Interior
SHARQ Infested Waters
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 Surveys (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.
In addition to investigations of coral reef metabolism, the SHARQ has been used to study bottom-dwelling, or benthic, communities in Florida Bay and marine "whitings" in the Bahamas.
Florida Bay is a shallow body of water that lies between the Florida Keys and the southernmost coast of Florida. During the last century humans have altered the landscape of South Florida and changed the Florida Bay environment. As a result, land and water use managers have undertaken a program to restore Florida Bay to a more natural state.
USGS researchers (in collaboration with Everglades National Park, the South Florida Water Management District, the Fish and Wildlife Conservation Commission, and the University of Miami) are using the SHARQ to determine baseline metabolism rates of many benthic communities in addition to coral reefs, such as seagrass beds and algal mats, and to measure carbonate sediment production in Florida Bay. As new water management practices are put in place and restoration efforts progress, continued monitoring of these benthic communities will reveal their response to environmental changes in the Bay. Managers will then be able to assess whether the changes in the marine communities are what were intended, and to evaluate the success of efforts to restore the Bay to a more natural state.
The phenomenon known as "whitings" (patches of water approximately 1 to 2 kilometers in length and width that appear milky-white due to suspended calcium carbonate sediment) occurs in the Bahamas and many shallow, tropical seas around the world. Whitings are dynamic, constantly changing shape as they move with tidal and wind-driven currents, making it difficult to investigate them during the day and impossible at night. Determining the significance of whiting formation in carbon cycling and sediment budgets has been problematic due to conversies on the origin of whitings. Much of this controversy has resulted from difficulties in measuring geochemical changes in whitings that indicate whether the carbonate sediment is made in the water column or resuspended from the bottom.
Recently, USGS and University of South Florida investigators have shown that whitings are associated with blooms of microbes such as blue-green algae and unicellular green algae. USGS scientists have been funded by the Department of Energy to examine the role of microbes in whitings formation and the effects of this phenomenon on carbon dioxide cycling. Using the SHARQ, researchers trapped whitings water on the Bahamas Bank and, for the first time ever, measured geochemical changes in whitings over 24 hour time periods. Results from these studies indicate that calcium carbonate sediment in whitings is precipitated from seawater.
It is well known that inorganic calcium carbonate sediment production generates carbon dioxide. USGS scientists also measured air-sea carbon dioxide fluxes in whitings, for the first time, using a floating bell that traps a small volume of air directly over the waters surface. These measurements indicate that carbonate sediment production in whitings does not generate carbon dioxide and suggests that sediment production in whitings is linked to microbial metabolism. These findings are significant because they suggest that whitings formation may act as a sink for carbon dioxide.
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For more information contact:
Dr. Kimberly Yates
SOFIA Project: Geochemical Monitoring of Restoration Progress
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 15 January, 2013 @ 12:43 PM (KP)