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

Dissolution of coccolithophorid calcite by microzooplankton and copepod grazing

International audienceIndependent of the ongoing acidification of surface seawater, the majority of the calcium carbonate produced in the pelagial is dissolved by natural processes above the lysocline. We investigate to what extent grazing and passage of coccolithophorids through the guts of copepods and the food vacuoles of microzooplankton contribute to calcite dissolution. In laboratory experiments where the coccolithophorid Emiliania huxleyi was fed to the rotifer Brachionus plicatilis, the heterotrophic flagellate Oxyrrhis marina and the copepod Acartia tonsa, calcite dissolution rates of 45?55%, 37?53% and 5?22% of ingested calcite were found. We ascribe higher loss rates in microzooplankton food vacuoles as compared to copepod guts to the strongly acidic digestion and the individual packaging of algal cells. In further experiments, specific rates of calcification and calcite dissolution were also measured in natural populations during the PeECE III mesocosm study under differing ambient pCO2 concentrations. Microzooplankton grazing accounted for between 27 and 70% of the dynamic calcite stock being lost per day, with no measurable effect of CO2 treatment. These measured calcite dissolution rates indicate that dissolution of calcite in the guts of microzooplankton and copepods can account for the calcite losses calculated for the global ocean using budget and model estimates

Copepod feeding and reproduction in relation to phytoplankton development during the PeECE III mesocosm experiment

International audienceWithin the frame of the Pelagic Ecosystem CO2 Enrichment (PeECE III) experiment, reproduction and feeding of the copepod Calanus finmarchicus was monitored in relation to phytoplankton development in two mesocosms, at present 1× (350 ?atm) and ca 3× present (1050 ?atm) CO2 concentrations, respectively. Both mesocosms showed rapid phytoplankton growth after the initial nutrient additions and reached maximum chlorophyll (Chl) a concentrations around day 10. Flow-cytometry and specific pigment analysis (HPLC-CHEMTAX), showed that diatoms and prymnesiophyceae (Emiliania huxleyi (Ehux) and other nanoplankton) dominated the biomass. Feeding and egg production rates of C. finmarchicus developed similarly in both mesocosms, and were positively correlated with Chla, Ehux, diatom and prymnesiophyceae concentrations. Although the total number of copepod nauplii recruited during the experiment was similar in 1× and 3×, significantly less nauplii were recruited in 3× during the peak of the bloom compared to in 1×. We conclude that the algae responsible for the higher biomass in 3× during the peak of the bloom (diatoms and Ehux), may have been relatively inferior food for C. finmarchicus naupliar recruitment, possibly due to a high C:N ratio (>8). Nevertheless, the 3 fold increase in CO2 concentration did not show any clear overall effect on bulk phytoplankton or zooplankton development over the whole experiment, suggesting a more complex coupling between increased CO2 and the nutritional status of the system

Extensive cross-disciplinary analysis of biological and chemical control of Calanus finmarchicus reproduction during an aldehyde forming diatom bloom in mesocosms

Egg and faecal pellet production and egg hatching success of the calanoid copepod Calanus finmarchicus were monitored over a period of 14 days (14-28 April, 2008) while fed water from 4 differently treated mesocosms and ambient water. Two of the mesocosms used were inoculated with the polyunsaturated aldehyde (PUA)-producing diatom Skeletonema marinoi, while 2 received only nutrient additions with or without silica. The mesocosms developed blooms of S. marinoi, mixed diatoms or the haptophyte Phaeocystis pouchetii, respectively. Faecal pellet production of C. finmarchicus increased with increasing food availability. Egg production increased with time in all mesocosms to a maximum single female production of 232 eggs female(-1) day(-1) (average of 90 eggs female(-1) day(-1)) and followed the development of ciliates and P. pouchetii, but was not affected by the observed high (up to 15 nmol L(-1)) PUA production potential of the phytoplankton. The hatching success of the eggs produced on the mesocosm diets was high (78-96%) and was not affected by either aldehydes in the maternal diet or exposure to the dissolved aldehydes in the water

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

Exploring the metabolism and mixture effects of the isothiazolinone biocides BIT and OIT in PLHC-1 cells

The powerful antimicrobial properties of isothiazolinones make them a common preservative in both industrial and consumer products. However, methylated deriva tives of isothiazolinones have been associated with concerning allergenic effects leading to stricter regulations. As a consequence, industries have turned to more lipophilic isothiazolinones, such as benzisothiazolinone (BIT) and octylisothiazoli none (OIT), which are less regulated. Similar effects have however been reported for exposures of BIT and OIT, highlighting the importance of expanding the knowledge about these compounds, to enforce stricter regulation and potentially controlling the isothiazolinones as a group. This study aimed to investigate the toxicodynamic and toxicokinetic responses in a fish liver cell model system, Poeciliopsis lucida hep atocellular carcinoma (PLHC-1) following exposure to BIT and OIT, alone and in mixture. Results from the ethoxyresorufin-O-deethylase (EROD) assay revealed no apparent induction of the common detoxification enzyme CYP1A after exposure to BIT and OIT. However, more data is needed for a more robust evaluation of whether the enzyme is involved in their metabolism. Analysis of cultured exposure media in high performance liquid chromatography (HPLC) demonstrated cellular biotransformation of BIT into a more polar metabolite. A rapid cellular uptake of OIT was observed, however no potential OIT metabolite could be detected, nei ther extracellularly nor intracellularly. A cytotoxic assessment was also conducted on exposed PLHC-1 cells investigating the mitochondrial activity and membrane in tegrity, common markers for cellular viability. Significant toxic effects were observed on both markers after exposure to 10 µM OIT, while no toxic effect was observed for the same concentration of BIT. However, co-exposure to these concentrations of OIT and BIT, displayed an even greater toxicity, indicating a synergistic mixture effect between the two. While this study provides valuable insights into the toxi codynamic and toxicokinetic profiles of BIT and OIT, highlighting the importance of considering mixture effects in assessing their potential health and environmental impacts, additional research is needed to fully understand their specific metabolic pathways and interaction mechanisms, to assess their long-term exposure effects

Multitrophic Interactions in the Sea: Assessing the Effect of Infochemical-Mediated Foraging in a 1-d Spatial Model

The release of chemicals following herbivore grazing on primary producers may provide feeding cues to carnivorous predators, thereby promoting multitrophic interactions. In particular, chemicals released following grazing on phytoplankton by microzooplankton herbivores have been shown to elicit a behavioural foraging response in carnivorous copepods, which may use this chemical information as a mechanism to locate and remain within biologically productive patches of the ocean. In this paper, we use a 1D spatial reaction-diffusion model to simulate a tri-trophic planktonic system in the water column, where predation at the top trophic level (copepods) is affected by infochemicals released by the primary producers forming the bottom trophic level. The effect of the infochemical-mediated predation is investigated by comparing the case where copepods forage randomly to the case where copepods adjust their vertical position to follow the distribution of grazing-induced chemicals. Results indicate that utilization of infochemicals for foraging provides fitness benefits to copepods and stabilizes the system at high nutrient load, whilst also forming a possible mechanism for phytoplankton bloom formation. We also investigate how the copepod efficiency to respond to infochemicals affects the results, and show that small increases (2%) in the ability of copepods to sense infochemicals can promote their persistence in the system. Finally we argue that effectively employing infochemicals for foraging can be an evolutionarily stable strategy for copepods

Does Public Managers’ Type of Education Affect Performance in Public Organizations?:A Systematic Review

Although scholars agree that public managers’ education could affect performance in public organizations, no attempt has been made to synthesize the empirical evidence on this relationship. Consequently, we ask, do public managers with a general management education, such as an MPA, or a specialist education, such as an MD in the context of a hospital, affect different types of performance in public organizations? Based on a preregistered systematic literature review, we find 548 effect sizes from 50 quantitative studies by screening more than 12,000 potentially eligible studies. Our meta-regression analyses show that specialist managers have a statistically significant small average advantage on field-specific performance compared to other managers, and that generalist managers have a statistically significant small average advantage on financial performance compared to other managers. Based on these results, we recommend that future research investigate the theoretical linkages between public managers’ education and performance in public organizations

Metabarcoding and metabolome analyses of copepod grazing reveal feeding preference and linkage to metabolite classes in dynamic microbial plankton communities

In order to characterize copepod feeding in relation to microbial plankton community dynamics, we combined metabarcoding and metabolome analyses during a 22-day seawater mesocosm experiment. Nutrient amendment of mesocosms promoted the development of haptophyte (Phaeocystis pouchetii)- and diatom (Skeletonema marinoi)-dominated plankton communities in mesocosms, in which Calanus sp. copepods were incubated for 24 h in flow-through chambers to allow access to prey particles (<500 μm). Copepods and mesocosm water sampled six times spanning the experiment were analysed using metabarcoding, while intracellular metabolite profiles of mesocosm plankton communities were generated for all experimental days. Taxon-specific metabarcoding ratios (ratio of consumed prey to available prey in the surrounding seawater) revealed diverse and dynamic copepod feeding selection, with positive selection on large diatoms, heterotrophic nanoflagellates and fungi, while smaller phytoplankton, including P. pouchetii, were passively consumed or even negatively selected according to our indicator. Our analysis of the relationship between Calanus grazing ratios and intracellular metabolite profiles indicates the importance of carbohydrates and lipids in plankton succession and copepod–prey interactions. This molecular characterization of Calanus sp. grazing therefore provides new evidence for selective feeding in mixed plankton assemblages and corroborates previous findings that copepod grazing may be coupled to the developmental and metabolic stage of the entire prey community rather than to individual prey abundances

Adherence to the PRISMA-P 2015 reporting guideline was inadequate in systematic review protocols

Objectives: The objective of the study was to investigate to which degree systematic review protocols adhere to the Preferred Reporting Items for Systematic review and Meta-Analysis Protocols (PRISMA-P) reporting guideline. Study Design and Setting: We randomly sampled 50 publications of systematic review protocols indexed in PubMed and 50 protocols uploaded to the International Prospective Register of Systematic Reviews (PROSPERO) from 2016 onward. Two authors independently extracted data and assessed adherence to the 26 items specified by PRISMA-P. For each protocol, we categorized adherence to PRISMA-P as complete (≥90% of PRISMA-P items were fully reported) or partial (≥60% of PRISMA-P items were fully reported). We also assessed adherence to each PRISMA-P item across the protocols. Results: Four (8%) of the PubMed-indexed protocols adhered completely and 45 (90%) adhered partially to PRISMA-P but with considerable variation. None (0%) of the PROSPERO-uploaded protocols adhered completely and only 6 (12%) adhered partially to PRISMA-P. For both types of protocols, aspects related to the role of the sponsor, procedures for doing qualitative data synthesis if quantitative synthesis is not appropriate, and methods for assessing publication or outcome reporting biases and confidence in cumulative evidence were often not reported. Conclusion: Adherence to the PRISMA-P reporting guideline was somewhat inadequate in PubMed-indexed protocols and clearly inadequate in PROSPERO-uploaded protocols. Authors of systematic review protocols who decide to report according to PRISMA-P should carefully check all items included in the guideline, and journal editors and peer reviewers should consider PRISMA-P adherence when reviewing protocols for potential publication.</p