Variability in ultraplankton at the Porcupine Abyssal Plain study site |
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| Institution: | 1. Littoral, Environnement et SociétéS (LIENSs), Université de La Rochelle, UMR 7266, CNRS-ULR, 2 rue Olympe de Gouges, 17000 La Rochelle Cedex, France;2. Laboratoire Microorganismes, Génome et Environnement, UMR 6023, CNRS-Université de Clermont-Ferrand II, 24 avenue des Landais, 63177 Aubière Cedex, France;3. Laboratoire d''Ecogéochimie des Environnements Benthiques, UMR 8222, CNRS/UPMC, Observatoire Océanologique de Banyuls-sur-Mer, 66650 Banyuls-sur-Mer, France;4. Laboratoire Ressources Halieutiques de La Rochelle, Ifremer, Station de La Rochelle, Place Gaby Coll, BP 7, 17137 L''Houmeau, France;5. LEMAR, UMR 6539, Institut Universitaire Européen de la Mer, Place Nicolas Copernic, 29280 Plouzané, France;6. Université de Caen Basse-Normandie, FRE3484 BioMEA, CNRS, Esplanade de la Paix, F-14032 Caen, France;1. State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources and School of Life Sciences, SunYat-Sen University, Guangzhou 510275, China;2. Geological Institute, Russian Academy of Sciences, Moscow 119017, Russia;3. Borissiak Paleontological Institute, Russian Academy of Sciences, Moscow 117647, Russia;4. Cherepovets State University, Vologda Region, Cherepovets 162600, Russia;1. Marine Biology Station, National Institute of Biology, Forna?e 41, SI-6330 Piran, Slovenia;2. Institute of Marine Biological Resources & Inland Waters, Hellenic Centre for Marine Research, Anavissos GR-19013, Greece;1. Molecular Health and Disease Laboratory, University of Derby, DE22 1GB, UK;2. European Union Reference Laboratory for Crustacean Diseases, CEFAS, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, UK |
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| Abstract: | Observations of the ultraplankton (<5 μm) are presented from a 4 day mesoscale survey centred on the Porcupine Abyssal Plain (PAP) study site (49°00’N 16°30’W), in July 2006. The organisms enumerated include two groups of phytoplankton, Synechococcus cyanobacteria, heterotrophic bacteria, large viruses, and two size classes of heterotrophic protist. The dataset comprises over 400 samples from the mixed layer taken over a 100 × 100 km2 area at a spatial resolution of typically 2-3 km.For phytoplankton and heterotrophic bacteria there is a clear bimodal structure to the histograms of abundance indicative of two distinct communities in the region. Using the strong bimodality of one of the phytoplankton groups’ histogram as a basis, the dataset is split into two subsets, with roughly 200 points in each, corresponding to the two histogram peaks. Doing so provides evidence that Synechococcus and viruses may also have a bimodal structure. Correlations between all pairings of these five organisms (both phytoplankton groups, Synechococcus, heterotrophic bacteria and viruses) are positive and quite high (r>0.7). The two communities can therefore be characterised as high and low abundance. Although there is a coincidence of low abundances with high temperatures in the southwest corner of the region, where there was known to be an eddy present, the spatial distributions of these organisms over the whole region is poorly predicted by temperature (or salinity or density). Furthermore, the spatial distributions of heterotrophic protists are found to differ strongly from those of the other organisms, having a unimodal structure and no obvious large scale structure. The more random structure of the heterotrophs’ spatial distribution compared to their prey is consistent with previous results from the continental shelf, but is demonstrated for the open ocean here for the first time.Spatial variability is a large potential source of error in point samples, such as those comprising time series or transect cruises, unless a sufficient number of samples are taken. This large dataset is further used to provide guidance on the number of samples that would be required to estimate the mean abundance for the organisms accurately in this spatially variable region. Even if the bimodal structure was known initially, many of the organisms would require 10 or more samples to estimate the mean with 25% accuracy. |
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