Seasonal variations of community production, respiration and biomass of different primary producers in an intertidal Zostera noltii bed (Western English Channel, France)

Abstract

International audienceGross primary production (GPP) and respiration (R) in an intertidal Zostera noltii (Hornemann, 1832) community were estimated each month from in situ CO(2) flux measurements during the emersion period in the Bay of Morlaix (France). Simultaneously, the Chlorophyll a biomass of Z. noltii leaves, associated epiphytes and sediment within the benthic chambers were also monitored. The significant positive exponential relationship established between R and the maximum daily temperature emphasized that temperature was a good predictor of seasonal variation in the community R in Z. noltii bed. In contrast, the amplitude of the fitted curve on GPP was low and represented < 25% of the annual mean value (90.9 +/- A 15.2 mgC m(-2) h(-1)). The Chlorophyll a biomass of sediment was high (133.70 +/- A 22.96 mg m(-2)) but it was likely constituted by detritus which did not contribute much to the community GPP. The Chlorophyll a biomass of associated epiphytes was higher in winter and varied over the year inversely with Z. noltii. Therefore, the asynchronous dynamic of primary producers could support a constant rate of production at community scale over the year

Short Term CO2 Enrichment Increases Carbon Sequestration of Air-Exposed Intertidal Communities of a Coastal Lagoon

“…This suggests Z. noltei communities are more diverse and include more autotrophic organisms (e.g., epiphytes and benthic microalgae) (CharpyRoubaud and Sournia, 1990) contributing to the community production than sediment communities. Similar results of higher community production in Z. noltei than unvegetated sediment were observed at the Bay of Morlaix, France (Ouisse et al, 2010), and Banco de Mauritania (Clavier et al, 2014).…”

“…NCP and CR of Z. noltei are lower during exposed than when submerged under ambient conditions (Ouisse et al, 2010;Clavier et al, 2011), but under CO 2 enrichment conditions the community production is higher and CR lower as observed in our results. Lower CR during exposed condition may increase the overall community production of exposed Z. noltei compared to submerged conditions where CR rates are higher.…”

“…This suggests no photoinhibition of the whole community production at highest levels of PAR, which was also observed elsewhere for Z. noltei communities under ambient conditions (Ouisse et al, 2010(Ouisse et al, , 2011Clavier et al, 2011). Under CO 2 enriched conditions both communities increase their production even further without signs of saturation.…”

“…This may result from a reduction of CR under high CO 2 as observed here for both Z. noltei and unvegetated sediment communities and by an increase of the carboxylation rate mediated by RUBISCO as the CO 2 /O 2 ratio will increase. The LCP observed in our results were higher than previously reported for Z. noltei for both seasons under ambient conditions (Gacia et al, 2005;Ouisse et al, 2010) and lower for CO 2 enriched conditions. The LCPs of sediment community of both seasons under ambient conditions, were also higher than previously observed for sediment communities (Uthicke and Klumpp, 1998;Clavier and Garrigue, 1999).…”

“…There is a scarcity in utilization of IRGA for carbon flux measurements in the intertidal seagrasses. Most studies using carbon flux measurements on Z. noltei were performed in lab conditions (Leuschner and Rees, 1993;Perez-Loren and Niell, 1994;Leuschner et al, 1998), whereas few measurements have been performed in situ (Leuschner et al, 1998;Silva et al, 2005;Ouisse et al, 2010Ouisse et al, , 2011. In this context, we aimed to measure the short-term effects of high CO 2 concentration (750 ppm) on the net community production (NCP) and community respiration (CR) of air exposed Z. noltei community in Ria Formosa Lagoon, Portugal, where the species dominates the intertidal zone.…”