Estimating Seagrass Community Metabolism Using Benthic Chambers: The Effect of Incubation Time

Seagrass meadows are highly productive ecosystems that provide high-value ecosystem services and significantly contribute to carbon sequestration. Net community production (NCP) and community respiration (CR) in seagrass meadows are usually estimated from changes in oxygen concentration during in situ incubations in benthic chambers. Nevertheless, incubation chambers prevent water renovation, thus leading to an increase in pH and O2 and a possible super-saturation inside the chamber, particularly during daytime at high irradiances. We tested the effect of incubation time on seagrass meadows NCP using benthic chambers in a pristine Posidonia oceanica meadow in Corsica, France. Incubations lasting 1.5–2, 3–5, 12, and 24 h were conducted along the day. The results showed that NCP closely follows dial irradiance pattern, with maximum NCP values (23.1 ± 2.8 mmol O2 m−2 h−1) obtained for 1.5-2 h incubations at solar noon. A significant underestimation of NCP budgets was detected with increasing incubation times. When compared to 1.5-2 h incubations, the daylight NCP values obtained for 3-5 h and 12 h incubations underestimated NCP by 24 and 44 %, respectively, while 12 h night incubations underestimated CR by 63 %. When daily budgets were estimated, NCP calculated from 12 and 24 h incubations, the most used incubation times to estimate NCP in P. oceanica, underestimated it by 19 and 76 %, respectively, when compared to the daily budget obtained from 1.5-2 h incubations. Other factors, such as chamber volume and enclosed biomass, in conjunction with incubation time, are also discussed. We showed here that the values of P. oceanica NCP presently reported in the literature may be considerably underestimated. The role of this community as a key carbon sink in the Mediterranean may thus be underrated.