A comparison of four methods for determining planktonic community production1

Samples from two coastal experimental ecosystems were incubated in vitro and sampled over 24 h. Production rates were measured by the 14 C method, the O 2 and CO 2 light‐dark bottle methods, and the 18 O method. O 2 production in the experimental enclosures (volume ∼ 1.3 × 10 4 liters) was also measured directly. Photosynthetic and respiratory quotients were close to 1.0. Gross production values determined by O 2 light‐dark experiments, CO 2 light‐dark experiments, and 18 O were similar. 14 C production ranged from 60 to 100% of gross production measured in CO 2 light‐dark experiments, indicating that 14 C uptake is not precisely fixed with respect to other measures of community metabolism. There was no evidence that 14 C or any other method underestimated the rate of primary production in vitro by more than 40%. Productivities in vitro ranged from 35 to 100% of those in the mesocosm at similar light intensities. In samples from one of the ecosystems, the rate of respiration in the light (calculated from 18 O data) was an order of magnitude greater than the rate in the dark. This difference may be ascribed to either photorespiration or light enhancement of mitochondrial respiration.