Microzooplankton grazing and phytoplankton growth in marine mesocosms with increased CO2 levels

Microzooplankton grazing and algae growth responses to increasing pCO2 levels (350, 700 and 1050 μatm) were investigated in nitrate and phosphate fertilized mesocosms during the PeECE III experiment 2005. Grazing and growth rates were estimated by the dilution technique combined with taxon specific HPLC pigment analysis. Microzooplankton composition was determined by light microscopy. Despite a range of up to 3 times the present CO2 levels, there were no clear differences in any measured parameter between the different CO2 treatments. During days 3–9 of the experiment the algae community standing stock, measured as chlorophyll a (Chl-a), showed the highest instantaneous grow rates (k=0.37–0.99 d−1) and increased from ca. 2–3 to 6–12 μg l−1, in all mesocosms. Afterwards the phytoplankton standing stock decreased in all mesocosms until the end of the experiment. The microzooplankton standing stock, that was mainly constituted by dinoflagellates and ciliates, varied between 23 and 130 μg C l−1 (corresponding to 1.9 and 10.8 μmol C l−1), peaking on day 13–15, apparently responding to the phytoplankton development. Instantaneous Chl-a growth rates were generally higher than the grazing rates, indicating only a limited overall effect of microzooplankton grazing on the most dominant phytoplankton. Diatoms and prymnesiophytes were significantly grazed (12–43% of the standing stock d−1) only in the pre-bloom phase when they were in low numbers, and in the post-bloom phase when they were already affected by low nutrients and/or viral lysis. The cyanobacteria populations appeared more affected by microzooplankton grazing which generally removed 20–65% of the standing stock per day

Build-up and decline of organic matter during PeECE III

Increasing atmospheric carbon dioxide (CO2) concentrations due to anthropogenic fossil fuel combustion are currently changing the ocean's chemistry. Increasing oceanic [CO2] and consequently decreasing seawater pH have the potential to significantly impact marine life. Here we describe and analyze the build-up and decline of a natural phytoplankton bloom initiated during the 2005 mesocosm Pelagic Ecosystem CO2 Enrichment study (PeECE III). The draw-down of inorganic nutrients in the upper surface layer of the mesocosms was reflected by a concomitant increase of organic matter until day t11, the peak of the bloom. From then on, biomass standing stocks steadily decreased as more and more particulate organic matter was lost into the deeper layer of the mesocosms. We show that organic carbon export to the deeper layer was significantly enhanced at elevated CO2. This phenomenon might have impacted organic matter remineralization leading to decreased oxygen concentrations in the deeper layer of the high CO2 mesocosms as indicated by deep water ammonium concentrations. This would have important implications for our understanding of pelagic ecosystem functioning and future carbon cycling

From metabolomics to natural plankton food webs interactions. Conclusions from a cross-disciplinary in situ mesocosm experiment

Nejstgaard, J. C. ... et. al.-- 2012 Ocean Sciences Meeting, 20-24 February 2012, Salt Lake City, Utah, USAIn April 2008 a cross-disciplinary group of 24 scientists from 7 countries conducted a mesocosm experiment using 7x11 m3 in situ enclosures with natural seawater on the Norwegian west coast. A controlled gradient of increasingly mono-specific blooms of the diatom Skeletonema marinoi was created, and used to investigate chemical signaling, metabolomics, food quality, copepod reproduction and plankton development. We summarize intriguing results spanning from comprehensive studies of in situ metabolomics to food web dynamics using a suite of novel and classical approaches. With the advent of new in situ targeted analytical approaches, we argue that mesocosms are excellent tools to study complex food web interactions including chemical signaling and net nutritional effects on the plankton ecosystemsPeer Reviewe

Quantitative PCR to estimate copepod specific feeding during a mesocosm study

International Symposium Aquatic Mesocosm Research: Recent achievements and future directions in Aquatic Mesocosm Research, 16-19 October 2012, Heraklion, Crete, GreecePeer Reviewe

Extensive cross disciplinary analysis of biological and chaemical control of Calanus finmarchicus reproduction and grazing response to an aldehyde forming diatom bloom in mesocosms.

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Effects of light availability on mixotrophy and microzooplankton grazing in an oligotrophic plankton food web: Evidences from a mesocosm study in Eastern Mediterranean waters

12 pages, 9 figures, 2 tablesPlankton biomass and composition in the pelagic zone of oceans is exposed to changes in availability of light and nutrients due to large-scale ocean circulation and water column stratification. We hypothesized that displacement of plankton from surface to deeper darker waters would not only favor heterotrophy over time, as previously suggested, but also first rapidly affect the level of mixotrophy and, consequently, overall microbial grazing in plankton food webs. To test this in an oligotrophic marine system we incubated Eastern Mediterranean water (from 10 m depth north of Crete in September 2010) in 2.8 m3 mesocosms simulating two different light intensities at the sampling station, surface waters (ca. 10 m; mesocosms L1) and deeper layers (ca. 50–60 m; mesocosms L4). The biomass and abundance of the main planktonic groups were monitored either daily or every second day, depending on the group. Microzooplankton grazing rates and the contribution of mixotrophic feeding were estimated by a combination of dilution experiments and incubations with live fluorescently labeled algae (LFLA). Although no nutrients were added to the mesocosms the chlorophyll a increased during the first 2 days of the experiment in both treatments. This increase resulted from phytoplankton growth in the light L1-mesocosm (autotrophic biomass was ca. doubled in L1 compared to L4), but was mostly due to photoadaptation of the algae in the L4-mesocosm, as indicated by lower carbon to chlorophyll a ratios. By the end of the experiment, the total biomass of protozoan and metazoan grazers in L1 was ca. twofold higher than in L4. The microzooplankton responded within the first 24 h, showing different grazing activity in L1 than in L4. Microzooplankton grazing rates on total Chl a were similar in both treatments; however, phytoplankton instantaneous growth rates were higher in the more illuminated mesocosm. This resulted in a closer coupling between both rates in L4, where all production was grazed daily, than in L1. Nevertheless, the overall flux of carbon through the microzooplankton was 33–60% higher in L1 compared to L4 throughout the experiment. The fraction of mixotrophy in the ciliate community varied in L1 (20–50%), but decreased over time in L4 from 50% to 30%. Our results do not support studies from freshwater, postulating that reduced light and nutrient limitation may increase herbivore production due to stoichiometric effects. Finally, we discuss how mixotrophy may bias rate estimates in dilution experimentsThis work was funded through projects CTM2009-08783 from the SpanishMinistry of Science and Innovation assigned to A.C. and projects LightDynamix, LiMic and LightCopFed from the European Union Seventh Framework Program (FP7/2007-2013) under grant agreement no. 228224, MESOAQUA, assigned to R.P. (LightDynamix), A.C., R.A.M., A.S., A.G. (LiMic) and S.I. (LightCopFed)Peer reviewe

Feeding response of the calanoid copepod Clausocalanus furcatus (Brady, 1883) under distinct light conditions

International Symposium Aquatic Mesocosm Research: Recent achievements and future directions in Aquatic Mesocosm Research, 16-19 October 2012, Heraklion, Crete, GreecePeer reviewe

The effect of egg vs. seston quality on hatching success, naupliar metabolism and survival of Calanus finmarchicus in mesocosms dominated by Phaeocystis and diatoms.

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Quantitative PCR to estimate copepod feeding

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