Estimation of Net Ecosystem Metabolism of Seagrass Meadows in the Coastal Waters of the East Sea and Black Sea using the Noninvasive Eddy Covariance Technique

Abstract

We measured the community-scale metabolism of seagrass meadows in Bulgaria (Byala [BY]) and Korea (Hoopo Bay [HP]) to understand their ecosystem function in coastal waters. A noninvasive in situ eddy covariance technique was applied to estimate net O-2 flux in the seagrass meadows. From the highquality and high-resolution time series O-2 data acquired over > 24 h, the O-2 flux driven by turbulence was extracted at 15-min intervals. The spectrum analysis of vertical flow velocity and O-2 concentration clearly showed well-developed turbulence characteristics in the inertial subrange region. The hourly averaged net O-2 fluxes per day ranged from-474 to 326 mmol O-2 m(-2) d(-1) (-19 +/- 41 mmol O-2 m(-2) d(-1)) at BY and from-74 to 482 mmol O2 m-2 d-1 (31 +/- 17 mmol O-2 m(-2) d(-1)) at HP. The net O-2 production rapidly responded to photosynthetically available radiation (PAR) and showed a good relationship between production and irradiance (P-I curve). The hysteresis pattern of P-I relationships during daytime also suggested increasing heterotrophic respiration in the afternoon. With the flow velocity between 3.30 and 6.70 cm s(-1), the community metabolism during daytime and nighttime was significantly increased by 20 times and 5 times, respectively. The local hydrodynamic characteristics may be vital to determining the efficiency of community photosynthesis. The net ecosystem metabolism at BY was estimated to be-17 mmol O-2 m(-2) d(-1), which was assessed as heterotrophy. However, that at HP was 36 mmol O-2 m(-2) d(-1), which suggested an autotrophic state.