Factors controlling the community structure of picoplankton in contrasting marine environments

The effect of inorganic nutrients on planktonic assemblages has traditionally relied on concentrations rather than estimates of nutrient supply. We combined a novel dataset of hydrographic properties, turbulent mixing, nutrient concentration, and picoplankton community composition with the aims of (i) quantifying the role of temperature, light, and nitrate fluxes as factors controlling the distribution of autotrophic and heterotrophic picoplankton subgroups, as determined by flow cytometry, and (ii) describing the ecological niches of the various components of the picoplankton community. Data were collected at 97 stations in the Atlantic Ocean, including tropical and subtropical open-ocean waters, the northwestern Mediterranean Sea, and the Galician coastal upwelling system of the northwest Iberian Peninsula. A generalized additive model (GAM) approach was used to predict depth-integrated biomass of each picoplankton subgroup based on three niche predictors: sea surface temperature, averaged daily surface irradiance, and the transport of nitrate into the euphotic zone, through both diffusion and advection. In addition, niche overlap among different picoplankton subgroups was computed using nonparametric kernel density functions. Temperature and nitrate supply were more relevant than light in predicting the biomass of most picoplankton subgroups, except for Prochlorococcus and low-nucleic-acid (LNA) prokaryotes, for which irradiance also played a significant role. Nitrate supply was the only factor that allowed the distinction among the ecological niches of all autotrophic and heterotrophic picoplankton subgroups. Prochlorococcus and LNA prokaryotes were more abundant in warmer waters (>20 ∘C) where the nitrate fluxes were low, whereas Synechococcus and high-nucleic-acid (HNA) prokaryotes prevailed mainly in cooler environments characterized by intermediate or high levels of nitrate supply. Finally, the niche of picoeukaryotes was defined by low temperatures and high nitrate supply. These results support the key role of nitrate supply, as it not only promotes the growth of large phytoplankton, but it also controls the structure of marine picoplankton communities.Ministerio de Economía y Competitividad | Ref. CTM2012-30680Ministerio de Economía y Competitividad | Ref. CTM2008-0626I-C03-01Ministerio de Economía y Competitividad | Ref. REN2003-09532-C03-01Ministerio de Economía y Competitividad | Ref. CTM2004-05174 -C02Ministerio de Economía y Competitividad | Ref. CTM2011-25035Xunta de Galicia | Ref. 09MMA027604PRXunta de Galicia | Ref. EM2013/021European Commission | Ref. FP7, n. 261860Ministerio de Economía y Competitividad | Ref. FJCI-641 2015-2571

Prospects on searches for baryonic Dark Matter produced in bb-hadron decays at LHCb

A model that can simultaneously explain Dark Matter relic density and the apparent matter anti-matter imbalance of the universe has been recently proposed. The model requires $b$-hadron branching fractions to Dark Matter at the per mille level. The $b$-hadrons decay to a dark sector baryon, $\psi_{\rm{DS}}$, which has a mass in the region $940$ MeV/c$^{2} \leq m(\psi_{\rm{DS}}) \leq 4430$ MeV/c$^{2}$. In this paper, we discuss the sensitivity of the LHCb experiment to search for this dark baryon, covering different types of topology and giving prospects for Runs 3 and 4 of the LHC, as well as for the proposed Phase-II Upgrade. We show that the LHCb experiment can cover the entire mass range of the hypothetical dark baryon.Comment: 8 pages, 7 figures, 2 table

Differential response of the toxic microalgae Alexandrium minutum to exudates of the seagrass Zostera marina and the invasive seaweed Gracilaria vermiculophylla

Poster.-- ASLO Aquatic Sciences Meeting 2023, Resilience and Recovery in Aquatic Systems, 4–9 June 2023, Palma de Mallorca, SpainInterspecific interactions are recognized as a key factor in the development of harmful algal blooms. Recently, a lower abundance of planktonic dinoflagellates has been reported associated with areas dominated by seagrasses, suggesting a negative interaction between these organisms. The widespread colonization of seagrass ecosystems by the invasive alga Gracilaria vermiculophylla may affect this interaction. Our experimental design consisted in the addition of different concentrations of exudates of the eelgrass Zostera marina and/or G. vermiculophylla to cultures of the toxic dinoflagellate Alexandrium minutum. Dinoflagellate growth rate and photosynthetic efficiency of PSII (Fv/Fm) were measured. DOC concentrations of the added exudates represented realistic values for the study area. A. minutum growth rate was significantly lower (up to 99.8%) in the treatments with Z. marina exudates than in the control. By contrast, the addition of exudates from the algae stimulated A. minutum growth rate by 7.8% as compared to the control, although this difference was not statistically significant. The results from A. minutum cultures treated with a combination of Z. marina and G. vermiculophylla exudates showed that the negative effect of the eelgrass on the dinoflagellate prevailed over the positive effect of the invasive algae. Our results suggest that the presence of healthy seagrass beds in estuarine ecosystems may control toxic dinoflagellate growth, even overcoming the potential stimulating effect of invasive macroalgaeThis research was supported by the INTERES (CTM2017-83362-R) and the BIOTOX (CTM2017-83362-R) projectsN

Latitudinal distribution of microbial plankton abundance, production and respiration in the Equatorial Atlantic in Autumn 2000.

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