By altering the nutritional quality of primary producers, nutrient availability indirectly influences herbivores' population dynamics. In turn, the resulting relationship between diet, growth, and wastes has consequences for nutrient cycling at the ecosystem level. We studied the link between dinoflagellates nutritional requirements and feeding behavior, and its influence on nutrient cycling. We show that long‐term shifts in dissolved PO4 concentration in the North Sea are closely linked to biomass trends of heterotrophic dinoflagellates and support this observation with experimental data indicating particularly high phosphorus requirements in dinoflagellates. At the seasonal scale, we observe a negative correlation between natural dinoflagellate abundances and the concentration of dissolved P, and we estimate that, in spring, up to 30% of dissolved P can end up in microzooplankton biomass. Our study highlights that accounting for organismal metabolic requirement provides significant insight in interpreting and predicting nutrient cycles at the ecosystem level.
Although consumers may use selective feeding to cope with suboptimal resource quality, little work has examined the mechanisms that underlie selective feeding, the efficiency of this behavior or its influence on consumer growth rate. Furthermore, a consumer’s exposure to suboptimal resources may also influence the consumer’s behavior and life history, including growth rate. Here, we studied how the availability of P-rich and P-poor phytoplankton influences the growth and behavior of copepod nauplii. We observed that copepod nauplii preferentially feed on P-rich prey. We also found that even relatively short exposure to P-rich phytoplankton yielded higher nauplii growth rates, whereas the presence of P-poor phytoplankton in a mixture impaired growth. Overall, we observed that swimming speed decreased with increasing phytoplankton P-content, which is a behavioral adjustment that may improve utilization of heterogeneously distributed high-quality food in the field. Based on our results, we propose that the optimal prey C: P ratio for copepod nauplii is very narrow, and that deviations from this optimum have severe negative consequences for growth.
<p>The Southern Ocean is known to be the largest High Nutrient Low Chlorophyll (HNLC) area of the global ocean, where algal development is mainly limited by iron (Fe) deficiency, except in few naturally Fefertilized areas (e.g. around Kerguelen plateau). The availability of different nutrients is unevenly distributed in this area. Thus, northwards the polar front, nitrogen and phosphorus (N and P) concentrations are high, but the scarcity of silicon (Si) limits the growth of diatoms (HN-LSi-LC). Further North, the Southern Indian Ocean is characterized by macronutrient limitation and low primary production (LNLC).</p><p>In these areas, atmospheric input could play a major role in the nutrient supply of primary producers. The main aim of this study is to assess the biological response of local phytoplankton communities to a deposition of two types of natural aerosols: desert dust and volcanic ash. Preliminary trace-metal clean laboratory experiments enabled us to quantify the abiotic dissolution of main macro- and micronutrients in dry and wet deposition mode of different natural aerosols of these types that yield us to choose Patagonia dust and ash from the Icelandic volcano Eyjafjallaj&#246;kull for our experiment at sea.</p><p><br>We set up a series of on-board trace-metal clean microcosm experiments in the contrasted biogeochemical conditions of the South Indian Ocean and Southern Ocean with addition of realistic amounts of dust and ash of respectively 2 and 25 mg.L<sup>-1</sup>. Experiments ran over 48 hours to evaluate the triggered primary production and cell abundances. Primary production was estimated by <sup>13</sup>C spike and biogenic Si (bSi) uptake rates were assessed by <sup>30</sup>Si spike. Parallel experiments with nutrient addition (dFe, DIP, DIN and dSi) along with flux cytometry for estimation of pico- and nanophytoplankton cells enabled us to determine which element(s) dissolved from the aerosols was responsible for the enhanced algal growth.</p><p><br>The highest CO<sub>2</sub> fixation rate of 50 mg.m<sup>-3</sup>.day<sup>-1</sup> was found at the natural Fe fertilized Kerguelen plateau station. Dust, ash and Fe addition triggered primary production, and CO<sub>2</sub> fixation doubled in these treatments. We recorded an enrichment of b<sup>30</sup>Si, indicating an increase of Si uptake rate, mostly stimulated by Fe addition. At the different HNLC stations (high N - low Si and high N - high Si), Fe and aerosol addition induced as well increased CO<sub>2</sub> fixation. In the northern LNLC stations, algal growth was stimulated by nitrogen addition as expected, but Fe, Si and aerosol addition also triggered a biological response from <em>Synechococcus</em> cyanobacteria and pico- and nanoeukaryotes.</p><p><br>Noteworthy, in most experiments the two contrasted aerosol types (desert dust and volcanic ash) at particle charges which varied over more than an order of magnitude triggered very similar biological responses in all of the sampled areas, even with distinct elementary and mineral compositions (e.g. the Icelandic volcano ash is 64 % amorphous and contains roughly twice the amount of Fe, P, Mn and<br>Zn compared to the Patagonian desert dust which is only 48 % amorphous).</p>
Contrasting concentrations of macronutrients and micronutrients induce different nutrient limitations of the oceanic productivity and shape the composition of the phytoplankton communities of the South Indian Ocean and Indian sector of the Southern Ocean. o assess the phytoplankton response to nutrient release by desert dust and volcanic ash aerosols in these distinct biogeochemical regions, we conducted microcosm incubation experiments. A dry or wet deposition of either dust from Patagonia or ash from the Icelandic volcano Eyjafjallajökull or dissolved nutrients (Si, Fe, N and/or P) were added to trace metal clean incubations of surface seawater collected from five stations. These deposition experiments enabled the measurement of the biological response along with solubility calculations of nutrients. Both types of aerosols alleviated the iron deficiency occurring in the Southern Ocean during austral summer and resulted in a 24–110% enhancement of the primary production, depending on the station. The release of dissolved silicon may also have contributed to this response, although to a lesser extent, whereas neither the dust nor the ash relieved the nitrogen limitation in the low‐nutrient and low‐chlorophyll area. Diatom growth was responsible for 40% to 100% of the algal biomass increase within the responding stations, depending on the region and aerosol type. The high particle concentrations that are characteristic of ash deposition following volcanic eruptions may be of equal or higher importance to phytoplankton compared to desert dust, despite ashes' lower nutrient solubility to the ocean.
<p>The major climatic forcing parameters on Earth climate are temperature and the atmospheric concentrations of CO<sub>2</sub>. Even if their evolutions covaried to the first-order, the geological record show periods with non-linear evolution between those two parameters. Such delinking requires accurate paleoclimate reconstructions with implications for the modelling studies of our future climate.</p> <p><em>p</em>CO<sub>2</sub> and Sea Surface Temperature (SST) reconstructions are usually quantified using proxies relying on both the organic matter produced by coccolithophores (UK37&#8217; index and &#948;<sup>13</sup>C<sub>alkenones</sub>) and calcite of foraminiferal tests (&#948;<sup>11</sup>B, &#948;<sup>18</sup>O, Mg/Ca). These proxies have been very useful for a variety of paleoclimatic advances, yet present unresolved and potentially important biases. As an example, alkenone carbon isotopes are not able to register low to moderate <em>p</em>CO<sub>2</sub> levels (Badger et al., 2019). This is notoriously a major issue for paleoclimate reconstructions of the last 6 My (Plio-Pleistocene period).</p> <p>Our approach is to use a unique archive &#8211; the coccoliths &#8211; for determination of coeval SST and <em>p</em>CO<sub>2</sub>. Coccoliths are small calcite plates produced by unicellular photosynthetic algae called coccolithophores. They are a very promising substrate to analyse for paleoclimate studies because they calcify in the uppermost water column and because their isotopic ratios are sensitive to both photosynthesis and calcification (Hermoso et al. 2020). Therefore, these isotopic ratios provide physiological and metabolic information about coccolithophores of the past. In order to infer paleoclimates from the sedimentary archives, we have to deconvolve the isotopic biological imprint (vital effect) from the environment signal. For the evaluation of the vital effects, we have undertaken a large-scaled culture experiments with various strains of coccolithophore grown under various CO<sub>2</sub> concentrations and pH (Le Guevel et al. in prep). Even if we have managed culture until 1400ppm and 7.55 unit of pH, we were particularly interested in low <em>p</em>CO<sub>2</sub> and high pH conditions because the bibliography is lacking of vital effect for Plio-Pleistoc&#232;ne applications. All the selected strains produce coccoliths within the size range of the one we find predominantly in the marine sediments throughout geological times.</p> <p>We document a large decrease of the carbon differential vital effect with the CO<sub>2</sub> concentration increase between <em>Gephyrocapsa oceanica</em> and <em>Coccolithus braarudii</em>. This is consistent with previous studies but the absolute values are slightly different and we provide a more precise dataset at low to moderate <em>p</em>CO<sub>2</sub> than the previous ones (Rickaby et al., 2010; Hermoso et al., 2016). We propose the first study of the oxygen and carbon vital effect of the <em>Helicosphaera carteri</em> group with combined CO<sub>2</sub>/pH changes. Taken together, the culture data and measurements of the isotopic composition of the calcite biominerals allows better paleoreconstructions of SST and aqueous CO<sub>2</sub>.</p>
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.