Seasonal compensation of microbial production and respiration in a temperate sea

Abstract

Gross oxygen production (GP), dark respiration (DR) and net community production (NCP) were studied for 16 mo in the euphotic layer of 3 stations through the coastal transitional zone of the southern Bay of Biscay, and related to hydrographic and nutrient conditions, phytoplankton biomass and C incorporation. Microbial O2 fluxes exhibited seasonal patterns linked to the seasonal cycle of water column stratification and mixing, with positive NCP during the spring, negative throughout the summer and close to zero in winter. This pattern was altered at coastal regions, where productive periods were linked to coastal upwelling, whereas in winter persistent net heterotrophy was measured, presumably in relation to increases in organic matter discharge of continental origin. The comparison of NCP with O2 anomaly and No3 concentration in the euphotic zone, the spatial and temporal scales studied and the prevalence of steady-state conditions offshore support the conclusion that the maintenance of summer heterotrophy in the region was based upon the consumption of the surplus of organic matter produced in spring. The uncoupling in the microbial auto-and heterotrophic metabolisms, based on the accumulation and delayed consumption of dissolved organic matter as a consequence of the processes controlling phytoplankton growth and microbial heterotrophic activity in temperate seas, would explain such a pattern. The close relationshp observed between the seasonal variability in NCP and the magnitude of spring net production and predictions derived from the seasonal cycles of O2 anomaly in middle latitudes and atmospheric O2 led us to conclude that the seasonal compensation of production and respiration processes is a characteristic of the dynamics of the pelagic ecosystem, at least in coastal temperate seas. The implications of this conclusion are of great relevance for the interpretation of new production and the estimation of the trophic status of the ocean from direct measurements of plankton net production.

Autotrophic and heterotrophic metabolism of microbial planktonic communities in an oligotrophic coastal marine ecosystem: seasonal dynamics and episodic events

“…Serret et al, 1999). This was also observed in the present study as bacterial production and respiration showed maxima following the GPP and Chl-a maximum.…”

“…as a consequence of increased dissolved primary production (Baines and Pace, 1991;Cole et al, 1988;Serret et al, 1999). Often, a phytoplankton bloom also occurs in fall (Moncoiffé et al, 2000;Alonso-Saez et al, 2008).…”

Dissolved organic carbon production by microbial populations in the Atlantic Ocean

“…Fixing and storage procedures, reagents, and standardization followed the recommendations of Grasshoff et al (1983). Dissolved oxygen concentration was measured through automated precision Winkler titration performed with a Metrohm DMS Titrino, using a potentiometric end-point detector as described in Serret et al (1999). In the AMT-6 cruise, five replicates of 60-cm 3 borosilicate glass bottles were used, and measurements of dissolved oxygen were made with an automated photometric Winkler titration system based on that described in Williams and Jenkinson (1982), as described in Serret et al (pers.…”

Plankton Respiration, Production, and Trophic State in Tropical Coastal and Shelf Waters Adjacent to Northern Australia

“…These differences could be due to differences in methodology or to spatio-temporal variation in metabolic balance. Spatio-temporal variation has been attributed to factors such as (1) changes in environmental conditions (e.g., temperature: Regaudie-de-Gioux and Duarte, 2012); (2) differences in the input and composition of nutrients (Martínez-García et al, 2010); (3) changes in plankton abundance and productivity of primary producers (Gasol and Duarte, 2000); (4) variation in the phytoplankton size structure and growth rate (Marañón, 2015); and (5) the amount and reactivity of the locally produced (autochthonous) and imported (allochthonous) organic matter (e.g., Serret et al, 1999;Robinson et al, 2002;Lønborg and Álvarez-Salgado, 2012).…”