Luis Felipe Artigas

Amazon River carbon dioxide outgassing fuelled by wetlands

River systems connect the terrestrial biosphere, the atmosphere and the ocean in the global carbon cycle. A recent estimate suggests that up to 3 petagrams of carbon per year could be emitted as carbon dioxide (CO2) from global inland waters, offsetting the carbon uptake by terrestrial ecosystems. It is generally assumed that inland waters emit carbon that has been previously fixed upstream by land plant photosynthesis, then transferred to soils, and subsequently transported downstream in run-off. But at the scale of entire drainage basins, the lateral carbon fluxes carried by small rivers upstream do not account for all of the CO2 emitted from inundated areas downstream. Three-quarters of the world’s flooded land consists of temporary wetlands, but the contribution of these productive ecosystems to the inland water carbon budget has been largely overlooked. Here we show that wetlands pump large amounts of atmospheric CO2 into river waters in the floodplains of the central Amazon. Flooded forests and floating vegetation export large amounts of carbon to river waters and the dissolved CO2 can be transported dozens to hundreds of kilometres downstream before being emitted. We estimate that Amazonian wetlands export half of their gross primary production to river waters as dissolved CO2 and organic carbon, compared with only a few per cent of gross primary production exported in upland (not flooded) ecosystems. Moreover, we suggest that wetland carbon export is potentially large enough to account for at least the 0.21 petagrams of carbon emitted per year as CO2 from the central Amazon River and its floodplains. Global carbon budgets should explicitly address temporary or vegetated flooded areas, because these ecosystems combine high aerial primary production with large, fast carbon export, potentially supporting a substantial fraction of CO2 evasion from inland waters.

Coastal bacterioplankton community diversity along a latitudinal gradient in Latin America by means of V6 tag pyrosequencing

The bacterioplankton diversity of coastal waters along a latitudinal gradient between Puerto Rico and Argentina was analyzed using a total of 134,197 high-quality sequences from the V6 hypervariable region of the small-subunit ribosomal RNA gene (16S rRNA) (mean length of 60 nt). Most of the OTUs were identified into Proteobacteria, Bacteriodetes, Cyanobacteria, and Actinobacteria, corresponding to approx. 80% of the total number of sequences. The number of OTUs corresponding to species varied between 937 and 1946 in the seven locations. Proteobacteria appeared at high frequency in the seven locations. An enrichment of Cyanobacteria was observed in Puerto Rico, whereas an enrichment of Bacteroidetes was detected in the Argentinian shelf and Uruguayan coastal lagoons. The highest number of sequences of Actinobacteria and Acidobacteria were obtained in the Amazon estuary mouth. The rarefaction curves and Good coverage estimator for species diversity suggested a significant coverage, with values ranging between 92 and 97% for Good coverage. Conserved taxa corresponded to aprox. 52% of all sequences. This study suggests that human-contaminated environments may influence bacterioplankton diversity.

Seasonal variability in microplanktonic biomasses in the Gironde dilution plume (Bay of Biscay): relative importance of bacteria

Abstract Bacterial and phytoplankton biomasses were estimated in a four-year study along a saline gradient (the dilution plume of the Gironde estuary on the Aquitanian continental shelf), by measuring bacterial abundance and mean cell volumes (epifluorescence counts) and chlorophyll-a concentrations (in vitro fluorescence). The spatial and temporal distribution of phytoplankton enabled us to determine the seasonal succession of algal blooms, sprouting in the marine waters of the inner shelf in early spring (picoplanktonic forms), reaching their annual maximum (10 μg L−1) in plume waters in advanced spring, and moving to estuarine waters in the summer (> 20 μm forms). Bacterial biomasses followed mainly a decreasing dilution gradient, especially in winter and early spring, with maximum estuarine values reaching 107 cell mL−1 (more than 30 % of small attached cells and more than 60 % of free small cocci), in accordance with estuarine discharges into the inner shelf zone. Moreover, plume waters showed an additionnal peak of bacterial numbers and mean cell volumes in early summer, with increasing proportions of larger rod- and vibrio-shaped bacteria. A clear morphometrical succession was followed in marine waters, from a majority of attached and coccal cells in winter, to maximal proportions of larger vibrio-shaped bacteria, inducing a maximal spring level of total abundance (2 × 106 cell mL−1) and high mean cell volumes (0.044 μm3), coinciding with the marine vernal bloom. Bacterial estimated biomass represented, consequently, a wide range of proportions compared to phytoplankton: only when a good correlation was found between them, bacterial-C/phytoplankton-C ratio was close to 1 4 , a correlation that improved in warmer periods, throughout different water types. Due to the relavitely narrow range of chlorophyll-a values, we could not find a high predictive correlation when pooling all the 4-year data, a relationship that has been outlined in important reviews by pooling together different aquatic systems. We noticed, however, that in the particular environment of our study (high inputs of particulate detritic matter) bacterial-C usually dominated the microbial pool (specially in estuarine and plume waters and in light-limited conditions). This dominance, added to the frequent dominance of small-sized phytoplankton, leads to an enhanced “microbial loop” activity, defining a “maintenance system” (oligotrophic conditions), which alternates with some eutrophic periods.

Impact of the Phaeocystis globosa spring bloom on the intertidal benthic compartment in the eastern English Channel: a synthesis.

From 1999 to 2005, studies carried out in the frame of regional and national French programs aimed to determine whether the Phaeocystis globosa bloom affected the intertidal benthic communities of the French coast of the eastern English Channel in terms of composition and/or functioning. Study sites were chosen to cover most of the typical shore types encountered on this coast (a rocky shore, an exposed sandy beach and a small estuary). Both the presence of active Phaeocystis cells and their degradation product (foam) did have a significant impact on the studied shores. The primary production and growth rates of the kelp Saccharina latissima decreased during the bloom because of a shortage of light and nutrient for the macroalgae. On sandy sediments, the benthic metabolism (community respiration and community primary production), as well as the nitrification rate, were enhanced during foam deposits, in relation with the presence of bacteria and active pelagic cells within the decaying colonies. In estuarine sediments, the most impressive impact was the formation of a crust at the sediment surface due to drying foam. This led to anoxic conditions in the surface sediment and resulted in a high mortality among the benthic community. Some organisms also tended to migrate upward and were then directly accessible to the higher trophic level represented by birds. Phaeocystis then created a shortcut in the estuarine trophic network. Most of these modifications lasted shortly and all the systems considered came back to their regular properties and activities a few weeks after the end of the bloom, except for the most impacted estuarine area.

An optimised protocol to prepare Phaeocystis globosa morphotypes for scanning electron microscopy observation

A preparation protocol for scanning electron microscopy (SEM) was adapted and tested to the observation of Phaeocystis globosa morphotypes. For extra colonial cells, critical point drying (CPD) gave satisfactory results while for intra colonial cells, preservation with Lugols iodine and/or glutaraldehyde followed by air-drying appeared as the most suitable method.

A new definition of Adenoides eludens, an unusual marine sand-dwelling dinoflagellate without cingulum, and Pseudadenoides kofoidii gen. & comb. nov. for the species formerly known as Adenoides eludens

ABSTRACT The species Amphidinium eludens, as described by Herdman (1922; Proc. Trans. Liverpool Biol. Soc. 36: 18) based on her drawing in fig. 1, has been investigated for the first time by scanning electron microscopy and phylogenetic analysis. The morphological and molecular data reveal that this species is distantly related to other known dinoflagellates. Balech [1956, Rev. Algol., n. ser. 2(1–2): 30] cited Amphidinium eludens Herdman (1922, fig. 1) as the basionym of the type of Adenoides, while he described and illustrated Amphidinium kofoidii Herdman (1922, fig. 2) as Adenoides eludens. As the nomenclatural rules do not allow the change of basionym, we have re-defined the genus Adenoides based on the characteristics of Amphidinium eludens Herdman (1922, fig. 1). The thecal plate formula of Adenoides eludens is Po, 5′, 6″, 0c, 3+s, 5′″, 3p, 1″″. This species lacks a cingulum. The apical pore complex resembles that of peridinioid dinoflagellates, while the absence of a cingular groove is reminiscent of desmokont prorocentroids. We also propose Pseudadenoides kofoidii gen. & comb. nov. based on Herdman’s 1922 fig. 2 of Amphidinium kofoidii which was described by Balech in 1956 and re-named Adenoides eludens.

High diversity of dinoflagellates in the intertidal sandy sediments of Wimereux (north-east English Channel, France)

Benthic dinoflagellates collected in spring–summer 2010 and 2011 from intertidal sandy sediments of the shore of Wimereux (north-east English Channel, France) were examined by light microscopy, and some of them by scanning electron microscopy. High dinoflagellate species richness, 70 species, was evidenced when compared to the plankton observed in the coastal waters of the north-east English Channel. The greatest difficulty in performing accurate species identification mainly concerned the heterotrophic species of Amphidinium sensu lato , the laterally flattened species of Amphidiniopsis , as well as some heterotrophic species of Thecadinium . Several undescribed species are here illustrated, mainly within these genera. The differences in size between species of Herdmania and Sabulodinium suggest the occurrence of at least a second species for these monotypic genera. The species Amphidiniopsis hexagona , A. rotundata , A. uroensis and Sinophysis minima are reported for the first time in the Atlantic Ocean and on European coasts. Although these species were only previously known from the Pacific Ocean, they should not necessarily be considered as newcomers or invasive species due to the scarce coverage of the previous studies on sand-dwelling dinoflagellates.

Estudio comparativo de la estructura del bacterioplancton en aguas del Mar Argentino mediante el método de pirosecuenciación 454 tag

A comparative study of bacterioplankton structure in Argentinian Sea waters by the 454 - tag pyrosequencing method. The present study provides the first information about diversity and abundance of microbial communities in two environments of the Argentinian Sea by the 454 tag pyrosequencing technique. We observed more than 4,600 unique bacterial sequences from 36,188 tag amplicons, forming 280 phylotypes. In addition, nearly 2,700 unique se quences from more than 47,700 tags identified as Archaea, defined only 5 different phylotypes. The Jaccard distance (0.6 for bacteria and 0.2 for Archaea) indicated higher differences among bacteria rather than among Archaea in both studied sites. the dominant phylotypes in marine environment were Bacteroidetes Flavobacteriaceae, Proteobacteria Gammaproteobacteria, Proteobacteria Rhodobacteraceae and Proteobacteria Rickettsiales SAR11; and Pseudoalteromonadaceae Pseudoalteromonas, Proteobacteria Gammaproteobacteria, Proteobacteria Shewanella, Proteobacteria Rickettsiales SAR11 in the estuary sampling site. Archaea Euryarchaeota and Archaea Crenarchaeota were the major archaeal phylotypes found. the most abundant tag sequences included previously characterized taxa, although we also retrieved a large number of highly diverse, low-abundant phylotypes which constitute a largely unexplored “rare” biosphere. these microorganisms could have a crucial ecological role.