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  • 1
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    Phytoplankton Blooms at Increasing Levels of Atmospheric Carbon Dioxide: Experimental Evidence for Negative Effects on Prymnesiophytes and Positive on Small Picoeukaryotes (2017)
    Frontiers
    In:  Frontiers in Marine Science, 4 . Art.Nr. 64.
    Details
    Publication Date: 2020-02-06
    Description: Anthropogenic emissions of carbon dioxide (CO2) and the ongoing accumulation in the surface ocean together with concomitantly decreasing pH and calcium carbonate saturation states have the potential to impact phytoplankton community composition and therefore biogeochemical element cycling on a global scale. Here we report on a recent mesocosm CO2 perturbation study (Raunefjorden, Norway), with a focus on organic matter and phytoplankton dynamics. Cell numbers of three phytoplankton groups were particularly affected by increasing levels of seawater CO2 throughout the entire experiment, with the cyanobacterium Synechococcus and picoeukaryotes (prasinophytes) profiting, and the coccolithophore Emiliania huxleyi (prymnesiophyte) being negatively impacted. Combining these results with other phytoplankton community CO2 experiments into a data-set of global coverage suggests that, whenever CO2 effects are found, prymnesiophyte (especially coccolithophore) abundances are negatively affected, while the opposite holds true for small picoeukaryotes belonging to the class of prasinophytes, or the division of chlorophytes in general. Future reductions in calcium carbonate-producing coccolithophores, providing ballast which accelerates the sinking of particulate organic matter, together with increases in picoeukaryotes, an important component of the microbial loop in the euphotic zone, have the potential to impact marine export production, with feedbacks to Earth's climate system.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.3389/fmars.2017.00064
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Photoacclimation to abrupt changes in light intensity by Phaeodactylum tricornutum and Emiliania huxleyi: the role of calcification (2012)
    Inter Research
    In:  Marine Ecology Progress Series, 452 . pp. 11-26.
    Details
    Publication Date: 2019-09-23
    Description: Phytoplankton experience strong and abrupt variations in light intensity. How cells cope with these changes influences their competitiveness in a highly dynamical environment. While a considerable amount of work has focused on photoacclimation, it is still unknown whether processes specific of phytoplankton groups (e.g. calcification and silicification) influence their response to changing light. Here we show that the diatom Phaeodactylum tricornutum and the coccolithophore Emiliania huxleyi respond to an abrupt increase in irradiance by increasing carbon fixation rates, decreasing light absorption through the decrease of light-harvesting pigments and increasing energy dissipation through the xanthophyll cycle. In addition, E. huxleyi rapidly increases calcium carbonate precipitation in response to elevated light intensity, thereby providing an additional sink for excess energy. Differences between the 2 species also emerge with regard to the magnitude and timing of their individual responses. While E. huxleyi show a pronounced decrease in chlorophyll a and fucoxanthin cellular contents following increased light intensity, P. tricornutum has a faster increase in diadinoxanthin quota, a slower decrease in Fv/Fm (ratio of variable to maximum fluorescence) and a stronger increase in organic carbon fixation rate during the first 10 min. Our findings provide further evidence of species-specific responses to abrupt changes in light intensity, which may partly depend on the phytoplankton functional groups, with coccolithophores having a supplementary path (calcification) for the rapid dissipation of excess energy produced after an abrupt increase in light intensity. These differences might influence competition between coexisting species and may therefore have consequences at the community level.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps09606
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Ocean acidification has different effects on the production of dimethylsulfide and dimethylsulfoniopropionate measured in cultures of Emiliania huxleyi and a mesocosm study: a comparison of laboratory monocultures and community interactions (2016)
    CSIRO
    In:  Environmental Chemistry, 13 (2). pp. 314-329.
    Details
    Publication Date: 2019-09-23
    Description: Environmental context. Approximately 25 % of CO2 released to the atmosphere by human activities has been absorbed by the oceans, resulting in ocean acidification. We investigate the acidification effects on marine phytoplankton and subsequent production of the trace gas dimethylsulfide, a major route for sulfur transfer from the oceans to the atmosphere. Increasing surface water CO2 partial pressure (pCO2) affects the growth of phytoplankton groups to different degrees, resulting in varying responses in community production of dimethylsulfide. Abstract. The human-induced rise in atmospheric carbon dioxide since the industrial revolution has led to increasing oceanic carbon uptake and changes in seawater carbonate chemistry, resulting in lowering of surface water pH. In this study we investigated the effect of increasing CO2 partial pressure (pCO2) on concentrations of volatile biogenic dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP), through monoculture studies and community pCO2 perturbation. DMS is a climatically important gas produced by many marine algae: it transfers sulfur into the atmosphere and is a major influence on biogeochemical climate regulation through breakdown to sulfate and formation of subsequent cloud condensation nuclei (CCN). Overall, production of DMS and DMSP by the coccolithophore Emiliania huxleyi strain RCC1229 was unaffected by growth at 900 μatm pCO2, but DMSP production normalised to cell volume was 12 % lower at the higher pCO2 treatment. These cultures were compared with community DMS and DMSP production during an elevated pCO2 mesocosm experiment with the aim of studying E. huxleyi in the natural environment. Results contrasted with the culture experiments and showed reductions in community DMS and DMSP concentrations of up to 60 and 32 % respectively at pCO2 up to 3000 μatm, with changes attributed to poorer growth of DMSP-producing nanophytoplankton species, including E. huxleyi, and potentially increased microbial consumption of DMS and dissolved DMSP at higher pCO2. DMS and DMSP production differences between culture and community likely arise from pH affecting the inter-species responses between microbial producers and consumers.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1071/EN14268
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Response of plankton community respiration under variable simulated upwelling events (2022)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: Climate change is expected to alter the intensity and frequency of upwelling in high productive coastal regions, thus impacting nutrient fluxes, primary productivity and consequently carbon cycling. However, it is unknown how these changes will impact the planktonic (phytoplankton and bacteria) community structure, which affects community respiration (CR) and hence the carbon available for sequestration or transfer to upper trophic levels. Here we present results from a 37-day mesocosm experiment where we examined the response of CR to nutrient additions by simulating upwelling events at different intensities (low, medium, high and extreme) and modes (singular and recurring additions). We also analysed the potential contribution of different plankton size classes and functional groups to CR. The trend in accumulated CR with respect to nutrient fertilisation (total nitrogen added during the experiment) was linear in the two modes. Microplankton (mostly diatoms) and nanoplankton (small flagellates) dominated under extreme upwelling intensities and high CR in both singular and recurring upwelling modes, explaining 〉65% of the observed variability in CR. In contrast, prokaryotic picoplankton (heterotrophic bacteria and autotrophic cyanobacteria) explained 〈43% of the variance in CR under the rest of the upwelling intensities and modes tested. Changes in planktonic community structure, while modulating CR variability, would regulate the metabolic balance of the ecosystem, shifting it towards net-heterotrophy when the community is dominated by small heterotrophs and to net-autotrophy when large autotrophs prevail; although depending on the mode in which nutrients are supplied to the system. This shift in the dominance of planktonic organism will hence affect not only CR but also carbon sequestration in upwelling regions
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Microzooplankton communities and their grazing of phytoplankton under artificial upwelling in the oligotrophic ocean (2023)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: Ocean artificial upwelling has been suggested to boost primary production and increase harvestable resources such as fish. Yet, for this ecosystem-based approach to work, an effective energy transfer up the food web is required. Here, we studied the trophic role of microzooplankton under artificial upwelling via biomass and community composition as well as grazing rates on phytoplankton. Using mesocosms in the oligotrophic ocean, we supplied nutrient-rich deep water at varying intensities (low to high) and addition modes (a Singular large pulse or smaller Recurring pulses). Deep-water fertilization created a diatom-dominated bloom that scaled with the amount of inorganic nutrients added, but also Synechococcus -like cells, picoeukaryotes and nanophytoplankton increased in abundance with added nutrients. After 30 days, towards the end of the experiment, coccolithophores bloomed under recurring upwelling of high intensity. Across all upwelling scenarios, the microzooplankton community was dominated by ciliates, dinoflagellates (mixo- and heterotrophic) and radiolarians. Under the highest upwelling intensity, the average grazing rates of Synechococcus -like cells, picoeukaryotes and nanophytoplankton by microzooplankton were 0.35 d -1 ± 0.18 (SD), 0.09 d -1 ± 0.12 (SD), and 0.11 d -1 ± 0.13 (SD), respectively. There was little temporal variation in grazing of nanophytoplankton but grazing of Synechococcus -like cells and picoeukaryotes were more variable. There were positive correlations between abundance of these groups and grazing rates, suggesting a response in the microzooplankton community to prey availability. The average phytoplankton to microzooplankton ratio (biovolume) increased with added deep water, and this increase was highest in the Singular treatment, reaching ~30 (m 3 m -3 ), whereas the phytoplankton to total zooplankton biomass ratio (weight) increased from ~1 under low upwelling to ~6 (g g -1 ) in the highest upwelling but without a difference between the Singular and the Recurring mode. Several smaller, recurring upwelling events increased the importance of microzooplankton compared with one large pulse of deep water. Our results demonstrate that microzooplankton would be an important component for trophic transfer if artificial upwelling would be carried out at scale in the oligotrophic ocean.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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