Production and bacterial decomposition of dissolved organic matter in a fringing coral reef |
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| Authors: | Yasuaki Tanaka Hiroshi Ogawa Toshihiro Miyajima |
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| Institution: | (1) Marine Biogeochemistry Laboratory, Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa Chiba, 277-8564, Japan;(2) Present address: Tropical Biosphere Research Center, University of the Ryukyus, 3422 Sesoko, Motobu, Okinawa 905-0227, Japan |
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| Abstract: | The concentrations of dissolved organic carbon and nitrogen (DOC and DON, respectively) were measured in Shiraho fringing
reef (Japan), using a high-temperature catalytic-oxidation method. When the seawater on the reef flat (shallow lagoon) was
isolated from the surrounding ocean due to the low tide, the concentrations of DOC and DON on the reef flat were 66–75 and
4.8–5.7 μmol l−1, respectively. The DOC and DON concentrations were higher than those of the adjacent outer ocean (57–58 and 3.8 μmol l−1, respectively), suggesting that the coral reef functioned as a net source of dissolved organic matter for the surrounding
ocean. In order to investigate long-term bacterial decomposition of the reef-derived DOC (RF-DOC), the seawater samples collected
on the reef flat and at the adjacent ocean were incubated in the dark for 1 year. Regression analysis using an exponential
curve that considered two degradability pools (labile and refractory) fitted the mineralization of the RF-DOC very well (r
2 > 0.89). According to the regression analysis, the DOC produced on the reef flat was composed of the labile fraction of 63–94%
(average 77%) and the refractory fraction of 6–37% (average 23%). It was concluded that some of the DOC that was produced
in the coral reef ecosystem was exported to the surrounding ocean if the reef flat had a water residence time less than several
months. The exported organic matter may support microbial communities in the ocean as an energy source. |
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