Poor correlation between phytoplankton community growth rates and nutrient concentration in the sea

Nutrient availability is one of the major factors regulating marine productivity and phytoplankton community structure. While the response of phytoplankton species to nutrient variation is relatively well known, that of phytoplankton community remains unclear. We question whether phytoplankton community growth rates respond to nutrient concentration in a similar manner to phytoplankton species composing the community, that is, following Monod's model. Data on in situ marine community growth rates in relation to nutrient concentration and the behaviour of a simple multi-species community model suggest that community growth rate does not respond to nutrient concentration according to the Monod equation. Through a simulation study we show this can be explained as a consequence of changes in size structure. Marine biogeochemical models must not parameterize phytoplankton community growth rate response to nutrient concentration using a single Monod equation but rather involve different phytoplankton functional groups each with different equation parameters.Versión del editor3,859

The allometry of the smallest: superlinear scaling of microbial metabolic rates in the Atlantic Ocean

Prokaryotic planktonic organisms are small in size but largely relevant in marine biogeochemical cycles. Due to their reduced size range (0.2 to 1 mu m in diameter), the effects of cell size on their metabolism have been hardly considered and are usually not examined in field studies. Here, we show the results of size-fractionated experiments of marine microbial respiration rate along a latitudinal transect in the Atlantic Ocean. The scaling exponents obtained from the power relationship between respiration rate and size were significantly higher than one. This superlinearity was ubiquitous across the latitudinal transect but its value was not universal revealing a strong albeit heterogeneous effect of cell size on microbial metabolism. Our results suggest that the latitudinal differences observed are the combined result of changes in cell size and composition between functional groups within prokaryotes. Communities where the largest size fraction was dominated by prokaryotic cyanobacteria, especially Prochlorococcus, have lower allometric exponents. We hypothesize that these larger, more complex prokaryotes fall close to the evolutionary transition between prokaryotes and protists, in a range where surface area starts to constrain metabolism and, hence, are expected to follow a scaling closer to linearity.Versión del editor8,951

Temperature dependence of planktonic metabolism in the subtropical North Atlantic Ocean

The temperature dependence of planktonic metabolism in the subtropical North Atlantic Ocean was assessed on the basis of measurements of gross primary production (GPP), community respiration (CR) and net community production (NCP), as well as experimental assessments of the response of CR to temperature manipulations. Metabolic rates were measured at 68 stations along three consecutive longitudinal transects completed during the Malaspina 2010 Expedition, in three different seasons. Temperature gradients were observed in depth and at basin and seasonal scale. The results showed seasonal variability in the metabolic rates, the highest rates being observed during the spring transect. The overall mean integrated GPP / CR ratio was 1.39 ± 0.27 decreasing from winter to summer, and the NCP for the subtropical North Atlantic Ocean during the cruises exhibits net autotrophy (NCP > 0) in about two-thirds (66%) of the total sampled communities. Also, we reported the activation energies describing the temperature dependence of planktonic community metabolism, which was generally higher for CR than for GPP in the subtropical North Atlantic Ocean, as the metabolic theory of ecology predicts. Furthermore, we made a comparison of activation energies describing the responses to in situ temperature in the field (EaCR Combining double low line 1.64 ± 0.36 eV) and those derived experimentally by temperature manipulations (EaCR Combining double low line 1.45 ± 0.6 eV), which showed great consistency. © 2014 Author(s).This is a contribution to the Malaspina Expedition 2010, funded by the INGENIO 2010 CONSOLIDER program (ref. CDS2008-00077) of the Spanish Ministry of Economy and Competitiveness. L. S. García-Corral was supported by a JAE Pre-doc fellowship from the Spanish National Research Council (CSIC) and the BBVA Foundation, SpainPeer Reviewe

Data Paper. Data Paper

<h2>File List</h2><div> <p><a href="PhytoDataBase.zip">PhytoDataBase.zip</a> (MD5: ab5cf44ef2e8854d41e51a2aaf0a3ed5) consisting of: </p> <p><a href="Table1.csv">Table1.csv</a> (MD5: ca6261c88bfb388e0c3e4d58efac7a21)</p> <p><a href="Table2.csv">Table2.csv</a> (MD5: 0b3f4292975807b5f4ca6acc161cc17b)</p> <p><a href="Table3.csv">Table3.csv</a> (MD5: 6b068b352637f7108b648011af2aec27)</p> </div><h2>Description</h2><div> <p>Many macroecological theories have been developed to study the diversity on our planet. All these theories require the existence of consistent databases to test their predictions. In this work, we compiled a data set of marine microplankton species abundances at 788 stations with an extensive geographical coverage. Data were collected on different oceanographic cruises between 1992 and 2002. This database consists of abundances (cells/mL) for each species at each station and depth, together with estimates of the biomass and biovolume for each species. One of the key strengths in this database is that species identifications were made by the same taxonomist, which provides greater strength to the collection and ensures that estimates of species diversity are reliable. Environmental information has also been compiled at each station (chlorophyll, temperature, photosynthetically active radiation (PAR), nutrients) in order to have a characterization of the study area and to be used in studies on the environmental and biological controls of marine biodiversity.</p> <p><i>Key words</i>: <i>abundance; chlorophyll; diversity; microplankton; nutrients; photosynthetically active radiation; phytoplankton; temperature.</i></p> </div