The Coral Pulse of Life
Corals are marine organisms living in compact colonies of many identical individual polyps. The group includes the important reef builders that inhabit tropical oceans, which secrete calcium carbonate to form a hard skeleton. Coral reefs form some of the most diverse ecosystems on Earth. They occupy less than one tenth of one percent of the world ocean surface, yet they provide a home for about twenty-five percent of all marine species, including fish, molluscs, worms, and crustaceans. Paradoxically, coral reefs flourish even though they are often surrounded by ocean waters that provide few nutrients. University of Miami (UM) Rosenstiel School of Marine & Atmospheric Science scientist Chris Langdon and colleagues have developed a new tool to monitor coral reef vital signs. By accurately measuring their biological pulse, scientists can better assess how climate change and other ecological threats impact coral reef health worldwide.
During a March 2009 experiment at Cayo Enrique Reef in Puerto Rico, the team tested two new methods to monitor biological productivity. They compared a technique that measures changes in dissolved oxygen within a chamber that encloses an area of water above the reef with one that measures the flux of dissolved oxygen across the turbulent boundary layer above an unconfined portion of the seafloor.
By measuring dissolved oxygen production and consumption rates, scientists were able to monitor the balance between the production of new organic matter by the corals and algae and the consumption of that organic matter by the reef's heterotrophs, which are essential to assessing the health of coral reef ecosystems.
A combination of these methods is a valuable tool for assessing and studying the effects of climate change on coral reef health, according to the authors.
Coral reefs are fragile ecosystems, partly because they are very sensitive to water temperature. They are under threat from climate change, ocean acidification, overuse of reef resources, and harmful land-use practices, including urban and agricultural runoff and water pollution, which can harm reefs by encouraging excess algae growth.
Seaweed and algae proliferate given adequate nutrients and limited grazing by herbivores. Coral die if surrounding water temperature changes by more than a degree or two beyond their normal range or if water salinity drops. In an early symptom of environmental stress, corals expel their zooxanthellae; without their symbiotic algae, coral tissues become colorless as they reveal the white of their calcium carbonate skeletons, an event known as coral bleaching.
Measurements of biological productivity have typically been made by tracing changes in dissolved oxygen in seawater as it passes over a reef. However, this is a labor intensive and difficult method, requiring repeated measurements. The new method opens up the possibility of making long-term, unattended, high-temporal resolution measurements of photosynthesis and respiration of coral reefs and any other benthic ecosystems.
The study, titled "Productivity of a coral reef using boundary layer and enclosure methods" was published in the March issue of the journal Geophysical Research Letters.
For further information: http://www.eurekalert.org/pub_releases/2011-03/uomr-spn031711.php or http://europa.agu.org/?view=article&uri=/journals/gl/gl1103/2010GL046179/2010GL046179.xml&t=coral,productivity