Plankton dynamics in an estuarine plume: a mesocosm 13C and 15N tracer study

Abstract

Flows of carbon and nitrogen in a natural phytoplankton assemblage from the plume of the Scheldt estuary were followed during and after a light-induced bloom by measuring changes in concentrations and stable isotope ratios in mesocosms after addition of C-bicarbonate showed a strong coupling between algal primary production and bacterial secondary production, while addition of 13 C-glucose revealed bacteria as a carbon source for eukaryotes. Tracing the 13 C into mesozooplankton, we identified selective grazing on algae during the phytoplankton bloom, transfer of carbon from bacteria to mesozooplankton and opportunistic feeding strategies after the bloom. Nitrogen labeling confirmed carbon labeling findings, identified bacteria rather than mesozooplankton as ammonium regenerators and allowed quantification of nitrification. KEY WORDS: Plankton · Isotope · EstuarineResale or republication not permitted without written consent of the publisher

High bacterial carbon demand and low growth efficiency at a tropical hypereutrophic estuary: importance of dissolved organic matter remineralization

“…The low BGE, however, means that most of this up taken DOM is released as inorganic nutrients and CO 2 to the water column. The high bacterial production, similar to other tropical and temperate estuarine systems, suggests that this compartment also plays an important role as biomass sources for the next trophic levels LEE, 2011;TROUSSELLIER et al, 2005; VAN DEN MEERSCHE et al, 2011), but its major role in this system is as DOM remineralizer. The large allochthonous nutrient inputs along with the rapid DOM remineralization, supports the high primary productivity and biomass of the system (GUENTHER et al, 2015), which is the main source for the plankton consumers.…”

A <sup>13</sup>C labelling study on carbon fluxes in Arctic plankton communities under elevated CO<sub>2</sub> levels

“…13 C labelling combined with modelling has been used successfully in previous mesocosm studies, allowing quantifying carbon flows and interactions in plankton food webs (Van den Meersche et al, 2004, 2011de Kluijver et al, 2010). However, there are some assumptions and potential errors that need attention.…”

“…Engel et al, 2004b). Previous mesocosm studies focussed on nutrient replete situations and it was suggested that CO 2 effects on extracellular release would be more pronounced under nutrient limitation (Thingstad et al, 2008;de Kluijver et al, 2010). The results here show that bacterial production on phytoplankton exudation is also not enhanced with CO 2 in a post bloom situation.…”

“…The model is based on those of de Kluijver et al (2010) and Van den Meersche et al (2011). A detailed article about the model is in preparation (Van Engeland et al, 2012).…”

“…The conversion factor for phytoplankton was calculated as 0.06 (sum PLFA:OC) and 0.05 (sum PLFA:OC) for mixotrophs, based on phytoplankton culture and literature values (Dijkman et al, 2006). The conversion factor for bacterial carbon was 0.01 (sum PLFA/OC) (van den Meersche et al, 2004). The conversion factors were kept constant during the experiment.…”