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1. Heterotrophic Dinoflagellate Growth and Grazing Rates Reduced by Microplastic Ingestion

   https://doi.org/10.3389/fmars.2021.716349  

   Fulfer, Victoria M.; Menden-Deuer, Susanne (August 2021, Frontiers in Marine Science)

   Microplastics are ubiquitous contaminants in marine ecosystems worldwide, threatening fisheries production, food safety, and human health. Ingestion of microplastics by fish and large zooplankton has been documented, but there are few studies focusing on single-celled marine predators, including heterotrophic dinoflagellates. In laboratory experiments, the heterotrophic dinoflagellate species Oxyrrhis marina and Gyrodinium sp. readily ingested both algal prey and polystyrene microplastic spheres (2.5–4.5 μm), while Protoperidinium sp. did not ingest microplastics. Compared to algae-only fed dinoflagellates, those that ingested microplastics had growth rates reduced by 25–35% over the course of 5 days. Reduced growth resulted in a 30–50% reduction of secondary production as measured as predator biomass. Ingestion rates of algal prey were also reduced in the microplastic treatments. When given a mixture of microplastics and algal prey, O. marina displayed a higher selectivity for algal prey than Gyrodinium sp. Observations in the coastal ocean showed that phylogenetically diverse taxa ingested microplastic beads, and thus heterotrophic dinoflagellates could contribute to trophic transfer of microplastics to higher trophic levels. The results of this study may suggest that continued increase in microplastic pollution in the ocean could lead to reduced secondary production of heterotrophic protists due to microplastic ingestion, altering the flow of energy and matter in marine microbial food webs. 

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2. Phytoplankton growth and microzooplankton grazing rates from NES-LTER transect cruises, ongoing since 2018.

   https://doi.org/10.6073/PASTA/B3366E0D4206A401B415953ED3E60389  

   Menden-Deuer, Susanne; Marrec, Pierre (January 2023, Environmental Data Initiative)

   Phytoplankton growth and microzooplankton grazing rates were measured from incubation experiments using the dilution method in the framework of the Northeast U.S. Shelf Long-Term Ecological Research project. The data set includes plankton population dynamics rates obtained during 12 cruises from winter 2018 (EN608) to summer 2022 (EN687) along a north/south transect from Martha’s Vineyard to the shelf-break. Phytoplankton growth and microzooplankton grazing rates were measured for the total phytoplankton community (chl-a concentrations) and for size fractions (chl-a size fractionation) less than and greater than 10 µm. Phytoplankton growth and microzooplankton grazing rates, the first trophic interaction between primary producers and higher trophic levels, are essential parameters to assess the cycling and export of carbon in the ocean and to better understand marine food webs. 

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3. Herbivorous protist growth and grazing rates at in situ and artificially elevated temperatures during an Arctic phytoplankton spring bloom

   https://doi.org/10.7717/peerj.5264  

   Menden-Deuer, Susanne; Lawrence, Caitlyn; Franzè, Gayantonia (January 2018, PeerJ)

   To assess protistan grazing impact and temperature sensitivity on plankton population dynamics, we measured bulk and species-specific phytoplankton growth and herbivorous protist grazing rates in Disko Bay, West Greenland in April-May 2011. Rate estimates were made at three different temperatures in situ (0 °C), +3 °C and +6 °C over ambient. In situ Chlorophyll a (Chl a ) doubled during the observation period to ∼12  µg Chl a L −1 , with 60–97% of Chl a in the >20 µm size-fraction dominated by the diatom genus Chaetoceros. Herbivorous dinoflagellates comprised 60–80% of microplankton grazer biomass. At in situ temperatures, phytoplankton growth or grazing by herbivorous predators <200 µm was not measurable until 11 days after observations commenced. Thereafter, phytoplankton growth was on average 0.25 d −1 . Phytoplankton mortality due to herbivorous grazing was only measured on three occasions but the magnitude was substantial, up to 0.58 d −1 . Grazing of this magnitude removed ∼100% of primary production. In short-term temperature-shift incubation experiments, phytoplankton growth rate increased significantly (20%) at elevated temperatures. In contrast, herbivorous protist grazing and species-specific growth rates decreased significantly (50%) at +6 °C. This differential response in phytoplankton and herbivores to temperature increases resulted in a decrease of primary production removed with increasing temperature. Phaeocystis spp. abundance was negatively correlated with bulk grazing rate. Growth and grazing rates were variable but showed no evidence of an inherent, low temperature limitation. Herbivorous protist growth rates in this study and in a literature review were comparable to rates from temperate waters. Thus, an inherent physiological inhibition of protistan growth or grazing rates in polar waters is not supported by the data. The large variability between lack of grazing and high rates of primary production removal observed here and confirmed in the literature for polar waters implies larger amplitude fluctuations in phytoplankton biomass than slower, steady grazing losses of primary production. 

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4. Flows, growth rates, and the veering polynomial

   https://doi.org/10.1017/etds.2022.63  

   LANDRY, MICHAEL P.; MINSKY, YAIR N.; TAYLOR, SAMUEL J. (January 2022, Ergodic Theory and Dynamical Systems)

   Abstract For a pseudo-Anosov flow $$\varphi $$ without perfect fits on a closed $$3$$ -manifold, Agol–Guéritaud produce a veering triangulation $$\tau $$ on the manifold M obtained by deleting the singular orbits of $$\varphi $$ . We show that $$\tau $$ can be realized in M so that its 2-skeleton is positively transverse to $$\varphi $$ , and that the combinatorially defined flow graph $$\Phi $$ embedded in M uniformly codes the orbits of $$\varphi $$ in a precise sense. Together with these facts, we use a modified version of the veering polynomial, previously introduced by the authors, to compute the growth rates of the closed orbits of $$\varphi $$ after cutting M along certain transverse surfaces, thereby generalizing the work of McMullen in the fibered setting. These results are new even in the case where the transverse surface represents a class in the boundary of a fibered cone of M . Our work can be used to study the flow $$\varphi $$ on the original closed manifold. Applications include counting growth rates of closed orbits after cutting along closed transverse surfaces, defining a continuous, convex entropy function on the ‘positive’ cone in $H^1$ of the cut-open manifold, and answering a question of Leininger about the closure of the set of all stretch factors arising as monodromies within a single fibered cone of a $$3$$ -manifold. This last application connects to the study of endperiodic automorphisms of infinite-type surfaces and the growth rates of their periodic points. 

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5. Observed Sprite Streamer Growth Rates

   https://doi.org/10.1029/2024GL112537  

   Stenbaek‐Nielsen, H C; McHarg, M G; Liu, N Y (January 2025, Geophysical Research Letters)

   Abstract Sprites have been recorded at ∼100,000 frames per second. One hundred and sixty five essentially vertically propagating streamers, 110 downward and 55 upward, have been selected for analysis. The initial velocity increase is exponential as predicted by theory. Growth rates could be determined for 76 downward and 46 upward propagating streamers, and, in individual streamers, they are independent of altitude. The average growth rate increases from 1.6 10³in C‐sprites, to 2.6 10³in carrots, to 8.4 10³/s in jellyfish sprites. With a streamer model the driving electric field can be derived. Evaluating the field at 70 km altitude, we find fields of 98 (0.45 E_k), 121 (0.56 E_k), and 188 (0.87 E_k) V/m for the 3 sprite types, indicating that jellyfish sprites are the most energetic. High‐speed imaging can provide streamer growth rates and combined with a streamer model, the electric fields associated with various sprite features can be investigated. 

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