A comparison of four methods for determining planktonic community production1

Abstract

Samples from two coastal experimental ecosystems were incubated in vitro and sampled over 24 h. Production rates were measured by the ¹⁴C method, the O₂ and CO₂ light‐dark bottle methods, and the¹⁸O method. O₂ production in the experimental enclosures (volume ∼ 1.3 × 10⁴ liters) was also measured directly.Photosynthetic and respiratory quotients were close to 1.0. Gross production values determined by O₂ light‐dark experiments, CO₂ light‐dark experiments, and ¹⁸O were similar. ¹⁴C production ranged from 60 to 100% of gross production measured in CO₂ light‐dark experiments, indicating that ¹⁴C uptake is not precisely fixed with respect to other measures of community metabolism. There was no evidence that ¹⁴C 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 ¹⁸O 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.