Measuring Metabolism of Reefs in Virgin Islands National Park and Biscayne National Park: Signs of Trouble?

Rogers, Caroline

This is a submission to the Florida Caribbean Science Center about monitoring the stresses on coral reefs in Biscayne National Park and Virgin Islands National Park. Procedures are included It also includes an annotated draft at the end of the document. Over the last two decades, a variety of natural and human stresses have caused severe degradation of many reefs in the Caribbean and western Atlantic, including those within Virgin Islands National Park (VINP) and Biscayne National Park (BNP). Reefs are exhibiting declines in living coral and increases in algae. Calcification rates are changing because of a shift in the carbon balance between carbon used for constructing carbonate skeletons and carbon used to grow fleshy tissues of algae ("macroalgae"). To date, monitoring programs in VINP (e.g., Rogers et al. 1997) and BNP (e.g., Porter and Meier 1992) have focused on reef structure (e.g., abundances or cover of organisms) rather than reef function ("metabolism"). Calcification, the most fundamental process of all, involves the deposition of calcium carbonate, primarily by corals and coralline algae, which creates the 3-dimensional structure of the reef (see Hallock 1997). Scientists debate whether reefs are sources or sinks of COz, although most consider reefs as sources of COz over the time frame of interest to human beings because COz is released during the production of calcium carbonate (Hallock 1997, Hubbard 1997). Another essential process is productivity (photosynthesis and respiration) of reef organisms, including the zooxanthellae within the stony coral tissues and non-symbiotic algae (both turfs and macroscopic algae, or "macroalgae"). In this proposal we refer to calcification and productivity as reef "metabolism". There is an urgent need to determine the calcification rates of selected reefs within these national parks and to find out if these reefs are actively accreting or if they are unable to maintain their structure because the balance has shifted away from the major framework building organisms, including the scleractinian corals, to non-calcifying (or only weakly-calcifying) organisms (see Kinsey 1985). Presently, we know of no efforts to monitor calcification rates on reefs as indicators of reef condition. We need to determine if measurements of calcification rates and photosynthesis are useful tools for quantifying differences among reefs as well as changes on reefs over time (for example, before and during/ after bleaching episodes or runoff events). We plan to test and adapt methods which have recently been used successfully in seagrass beds in Florida Bay (Halley and Yates 1999). We propose to measure reef metabolism in Virgin Islands National Park and Biscayne National Park on reefs with a range of live coral cover during times of low and high water temperatures (winter and late summer/fall). Bleaching episodes, such as the most severe on record in 1998, are usually associated with higher than normal water temperatures. Water temperatures in both parks have exceeded 30 C, the temperature above which the symbiosis between corals and their zooxanthellae breaks down (Glynn and D'Croz 1990). We hope to measure reef metabolism before and during bleaching episodes. Additional outcomes of these measurements are an improved understanding of the COz contribution of coral reefs to the atmosphere and a methodology which can help to assess the direct impact of increased COz on coral reefs.