墾丁國家公園海域長期生態研究 - 整合與模式建構─南灣海域上層水體生物源有機碳循環及物理流場之研究-II(2/2)

To exam hourly responses of phytoplankton and heterotrophic bacteria to an upwelling
caused by spring tide, a 2-days cruise with 11 stations was conducted in the Nan-Wan Bay
coral reef ecosystem in Feb. 2001. Nitrate concentrations (NO3, <0.15 ~ 10.2 µM) correlated
negatively with temperature (16 ~ 26 oC). Estimated NO3 flux was ~60 mmolN m-2 h-1 with
<1% of it utilized by phytoplankton. Chlorophyll (Chl-a) concentrations doubled in 9 hrs after
the upwelling but with maximal concentrations <0.30 µg l-1. Daily euphotic zone integrated
primary production (IPPZe, 118 ~ 389 mgC m-2 d-1) and algal turnover rate (Pµ, 0.27 ~ 0.76 d-1)
responded to the upwelling ~5 hrs earlier than that of Chl-a. Such differential changes in
growth rates and biomass accumulation could be explained by the “conveyor-belt” theory.
The observed HNLC (High Nutrient Low Chlorophyll) phenomenon might due to shorter
residence time of water mass (<1 d) within the Bay in comparison with those of algal turnover
time (1.3 ~ 3.7 d). Euphotic zone integrated bacterial production (IBPZe; (7.2 ~3 9.7 mgC m-2
d-1) and bacterial turnover rate (0.56 ~ 0.82 d-1) were positively correlated with IPPZe, Pµ and
depth integrated POC (540 ~ 6575 mgC m-2, suggesting a high possibility of “bottom-up”
(organic substrate supply) control. This was confirmed by the results of 3 enrichment
experiments showing that bacterial growth was C-limited. Our study provide mechanistic
information regarding the magnitude of coupling among physical, chemical and biological
process since the time scale adopted by this study was similar to the turnover time of autoand
heterotrophic planktoners.