Biogeochemical cycling of carbon and nitrogen by the coral-zooxanthellae symbiosis.

摘要

Production of dissolved organic carbon (DOC) and nitrogen (DON) by symbiotic corals has been demonstrated. Three coral species were used for this investigation, including Diploria strigosa, Porites astreoides, and Porites divericata. During short-term incubations, the dissolved pools of carbon and nitrogen were monitored; changes in these pools were attributed to the symbiosis. DOM production occurred as several large pulse events overlying a more constant background production. Measured rates of DOC production range from 17 to 37 mug C · cm-2 · day -1 and agree with previously published rates. DOC production represents a significant pathway in the photoautotrophic carbon cycle of these animals. In the three species investigated, DOC production accounts for 11--21% of the dissolved inorganic carbon (DIC) drawdown. Released dissolved organic matter (DOM) tends to be rich in nitrogen, with DOC/DON ratios of 3/1 in both D. strigosa and P. divericata. This nitrogen-rich material, some of which is urea, has the potential to be an important source of carbon and nitrogen to the reef community. Extrapolating measured release rates of urea production for D. strigosa over the entire Bermuda platform, results presented demonstrate that corals are likely a dominant component of the seasonal urea cycle in this reef ecosystem.