Comparisons of net ecosystem metabolisms in typical habitats off tropic Samoa Island and their implications for ecological functions

Abstract

Net oxygen fluxes were measured using noninvasive eddy correlation methods to estimate the gross primary production (GPP), respiration (R), and net ecosystem metabolism (NEM) in coral reefs, an eelgrass meadow, and sandy sediments off Samoa Island. Abnormal sensor signals increased gradually after 24 h along with increasing numbers of epiphytes attaching to the sensor tips. Estimated net oxygen flux through 24 h (n = 96) from the coral reefs, eelgrass meadow, and sandy sediments measured in mmol O2 m&#8211 2 d&#8211 1 ranged from &#8211 288 to 2643 (mean 145), from &#8211 177 to 333 (mean &#8211 6), and from &#8211 463 to 999 (mean 55), respectively. The oxygen production and consumption were switched on and off dramatically with photosynthetically active radiation (PAR) intensity by photosynthesis and respiration, respectively, at all sites. In addition, the O2 fluxes were significantly correlated with ocean current velocities and wave heights. Interestingly, these were about three times higher in the sandy sediments than in the eelgrass meadow, which was expected to have much higher biomass. The GPP and R values in the coral reefs and eelgrass meadow were higher than in the sandy sediments, but the NEM values were ordered as follows: coral reefs > sandy sediments > eelgrass meadow. The coral reefs and sandy sediments were assessed as having autotrophy, but the eelgrass meadow demonstrated heterotrophy. Island. Abnormal sensor signals increased gradually after 24 h along with increasing numbers of epiphytes attaching to the sensor tips. Estimated net oxygen flux through 24 h (n = 96) from the coral reefs, eelgrass meadow, and sandy sediments measured in mmol O2 m&#8211 2 d&#8211 1 ranged from &#8211 288 to 2643 (mean 145), from &#8211 177 to 333 (mean &#8211 6), and from &#8211 463 to 999 (mean 55), respectively. The oxygen production and consumption were switched on and off dramatically with photosynthetically active radiation (PAR) intensity by photosynthesis and respiration, respectively, at all sites. In addition, the O2 fluxes were significantly correlated with ocean current velocities and wave heights. Interestingly, these were about three times higher in the sandy sediments than in the eelgrass meadow, which was expected to have much higher biomass. The GPP and R values in the coral reefs and eelgrass meadow were higher than in the sandy sediments, but the NEM values were ordered as follows: coral reefs > sandy sediments > eelgrass meadow. The coral reefs and sandy sediments were assessed as having autotrophy, but the eelgrass meadow demonstrated heterotrophy.