Seasonal and bleaching-induced changes in coral reef metabolism and CO2 flux

摘要

+AFs-1+AF0- Monitoring seawater CO2 for a full year with seasonal observations of community metabolism in Ishigaki Island, Japan, revealed seasonal variation and anomalous values owing to the bleaching event in 1998. The daily average pCO(2) showed a seasonal pattern on an annual scale, 280 to 320 mu atm in winter and 360 to 400 mu atm in summer, which was determined primarily by the seasonal change in seawater temperature. By contrast, the range in the diel variation in pCO(2), 400 to 500 mu atm in summer 200 to 300 matm in winter, was attributed to the seasonal variation in community metabolism: Gross primary production (P-g) and respiration ( R) were high in summer and low in winter. During the 1998 bleaching event, although Pg and R increased, community excess organic production ( E) decreased by three quarters compared with the same month in 1999, when the coral community showed high recovery. This change in metabolism led to large diel range and increased average value of pCO(2) levels in the seawater on the reef flat. The decrease in the range and increase in the average value of pCO(2) were observed by monitoring the Palau barrier reef flat, where overall mortality of corals occurred after the bleaching. All the metabolic parameters, Pg, R, E and calcification (G) were reduced by half after the bleaching, which increased the average pCO2 value by 10 matm and decreased its diel range from 200 - 400 mu atm to 100 - 200 mu atm. Bleaching and resultant mortality of coral reefs led to degradation of their metabolic performance, and thus resulted in the loss of their active interaction with the carbon cycle.