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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 20 | Copyright
Biogeosciences, 15, 6199-6220, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Oct 2018

Research article | 26 Oct 2018

Factors controlling the community structure of picoplankton in contrasting marine environments

Jose Luis Otero-Ferrer1, Pedro Cermeño2, Antonio Bode6, Bieito Fernández-Castro1,3, Josep M. Gasol2,5, Xosé Anxelu G. Morán4, Emilio Marañon1, Victor Moreira-Coello1, Marta M. Varela6, Marina Villamaña1, and Beatriz Mouriño-Carballido1 Jose Luis Otero-Ferrer et al.
  • 1Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo, Vigo, Spain
  • 2Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas, Barcelona, Spain
  • 3Departamento de Oceanografía, Instituto de investigacións Mariñas (IIM-CSIC), Vigo, Spain
  • 4King Abdullah University of Science and Technology (KAUST), Read Sea Research Center, Biological and Environmental Sciences and Engineering Division, Thuwal, Saudi Arabia
  • 5Centre for Marine Ecosystem Research, School of Sciences, Edith Cowan University, WA, Perth, Australia
  • 6Centro Oceanográfico de A Coruña, Instituto Español de Oceanografía (IEO), A Coruña, Spain

Abstract. 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.

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Short summary
The effect of inorganic nutrients on planktonic assemblages has been traditionally assessed by looking at concentrations rather than fluxes of nutrient supply. However, in near-steady-state systems such as subtropical gyres, nitrate concentrations are kept close to the detection limit due to phytoplankton uptake. Our results, based on direct measurements of nitrate diffusive fluxes, support the key role of nitrate supply in controlling the structure of marine picoplankton communities.
The effect of inorganic nutrients on planktonic assemblages has been traditionally assessed by...