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Fluorescence in situ hybridization (FISH) in combination with polynucleotide probes revealed that the two major groups of planktonic Archaea ( Crenarchaeota and Euryarchaeota ) exhibit a different distribution pattern in the water column of the Pacific subtropical gyre and in the Antarctic Circumpolar Current system. While Euryarchaeota were found to be more dominant in nearsurface waters, Crenarchaeota were relatively more abundant in the mesopelagic and bathypelagic waters. We determined the abundance of archaea in the mesopelagic and bathypelagic North Atlantic along a south-north transect of more than 4,000 km. Using an improved catalyzed reporter deposition-FISH (CARD-FISH) method and specific oligonucleotide probes, we found that archaea were consistently more abundant than bacteria below a 100-m depth. Combining microautoradiography with CARD-FISH revealed a high fraction of metabolically active cells in the deep ocean. Even at a 3,000-m depth, about 16% of the bacteria were taking up leucine. The percentage of Euryarchaeota and Crenarchaeaota taking up leucine did not follow a specific trend, with depths ranging from 6 to 35% and 3 to 18%, respectively. The fraction of Crenarchaeota taking up inorganic carbon increased with depth, while Euryarchaeota taking up inorganic carbon decreased from 200 m to 3,000 m in depth. The ability of archaea to take up inorganic carbon was used as a proxy to estimate archaeal cell production and to compare this archaeal production with total prokaryotic production measured via leucine incorporation. We estimate that archaeal production in the mesopelagic and bathypelagic North Atlantic contributes between 13 to 27% to the total prokaryotic production in the oxygen minimum layer and 41 to 84% in the Labrador Sea Water, declining to 10 to 20% in the North Atlantic Deep Water. Thus, planktonic archaea are actively growing in the dark ocean although at lower growth rates than bacteria and might play a significant role in the oceanic carbon cycle.

Size-fractionated chlorophyll-a and carbon incorporation rates were determined on a series of 13 cruises carried out from 1992 to 2001with the aim of investigating the patterns and causes of variability in phytoplankton chlorophyll and production in the Eastern North Atlantic Subtropical Gyral Province (NASE). Averaged (±SE) integrated chlorophyll-a concentration and primary production rate were 17±1 mg m−2 and 253±22 mg C m−2 d−1. Small-sized cells (

Slope Water anticyclonic Oceanic eDDIES (SWODDIES) are typical mesoscale features of open-ocean waters of the southern Bay of Biscay which usually develop in winter by shedding from the seasonal poleward current flowing along the northern Spanish slope. These eddies have been intensively studied from the physical perspective. However, their effect on the distribution of biological properties and on the functioning of the pelagic ecosystem has not been assessed so far. To this aim, a sea-truth, multidisciplinary and comprehensive study of a SWODDY was carried out in summer 1998. The eddy, radius of ≈50 km, was initially centred at 45·5°N 6·0°W, being characterized by a relatively homogeneous core of water in the centre of the eddy extending from 80 to about 200 dbar. In the central region of the core, temperature (12·55–12·75°C) and salinity (≈35·70) values were higher than outside the eddy. The optical properties of the eddy also differed from those of the surrounding waters. A distinct biological signature was found associated with the eddy. Depth-integrated chlorophyll-a concentrations were 25% higher at the eddy centre where upward doming of the seasonal pycnocline (up to 30 dbar) occurred. Enhanced phytoplankton biomass was related to a higher contribution of >10 μm cells, mainly represented by diatoms and chrysophyceans. Phytoplankton and mesozooplankton species composition in and outside the eddy differed significantly reflecting the coastal origin of the water parcel trapped by the eddy. The sharp modification of the planktonic community composition, biomass and associated size-structure caused by slope water oceanic eddies are likely to exert a significant effect upon the upper trophic levels of the pelagic ecosystem of the southern Bay of Biscay.

Ammonium regeneration and dissolved organic nitrogen (DON) release were studied experimentally in the euphotic zone of shelf and oceanic waters of NW Spain in relation to coastal upwelling dynamics and the size-structure of phytoplankton communities. Incubations of plankton labelled with [ 15 N]ammonium were made during four cruises, two of which also included size-fractionated determinations of chlorophyll a and primary production, and experimental determinations of production rates of dissolved organic carbon (DOC) using 14 C. Inorganic nitrogen concentrations were mainly related to nitrate enrichment by upwelling pulses, while ammonium concentrations were generally low in all situations. Ammonium did not accumulate in the study area, suggesting a daily time scale coupling between regeneration and uptake. In contrast, DON largely exceeded inorganic nitrogen in all situations and generally increased from spring to autumn. Ammonium regeneration was positively correlated with DON release and both rates showed the largest variation in summer, with minimum values during active upwelling and maximum values when upwelling relaxed. Comparison of DON stocks and rates in different shelf areas suggests that DON release near the coast during summer was more persistent in the water than DON release in off-shelf and oceanic areas. The carbon:nitrogen ratio of DOC and DON release rates was highly variable, revealing a large excess of DOC compared with DON. This excess can be attributed to either an underestimate of total DON release (as only release from ammonium was measured) or to an enhanced production of carbon-rich organic substances by diatoms in coastal areas. By considering a broad range of trophic situations, this study reveals a fundamental difference between short term release of DOC and DON by plankton. Physiological processes (such as carbohydrate exudation by diatoms) seem to be the cause of large DOC excess, whereas trophic processes (such as grazing) are more likely the cause of enhanced DON release.

27 páginas, 3 tablas, 5 figuras, Concurrent measurements of dark community respiration (DCR), gross production (GP), size fractionated primary production (14C PP), nitrogen uptake, nutrients, chlorophyll a concentration, and heterotrophic and autotrophic bacterial abundance were collected from the upper 200m of a latitudinal (321S–481N) transect in the Eastern Atlantic Ocean during May/June 1998. The mean mixed layer respiration rate was 2.572.1 mmol O2m 3 d 1 (n ¼ 119) for the whole transect, 2.271.1 mmol O2m 3 d 1 (n ¼ 32) in areas where chlorophyll a was o0.5 mgm 3 and 1.570.7 mmol O2m 3 d 1 (n ¼ 10) where chlorophyll a waso0.2 mgm 3. These values lie within the range of published data collected in comparable waters, they co-vary with indicators of heterotrophic and autotrophic biomass (heterotrophic bacterial abundance, chlorophyll a concentration, beam attenuation and particulate organic carbon concentration) and they can be reconciled with accepted estimates of total respiratory activity. The mean and median respiratory quotient (RQ), calculated as the ratio of dissolved inorganic carbon production to dissolved oxygen consumption, was 0.8 (n ¼ 11). At the time of the study, plankton community respiration exceeded GP in the picoautotroph dominated oligotrophic regions (Eastern Tropical Atlantic [15.51S–14.21N] and North Atlantic Subtropical Gyre [21.5–42.51N]), which amounted to 50% of the stations sampled along the 12,100km transect. These regions also exhibited high heterotrophic: autotrophic biomass ratios, higher turnover rates of phytoplankton than of bacteria and low f ratios. However, the carbon supply mechanisms required to sustain the rates of respiration higher than GP could not be fully quantified. Future research should aim to determine the temporal balance of respiration and GP together with substrate supply mechanisms in these ocean regions, CR was funded by a NERC Advanced Research Fellowship (GT5/96/8/MS), PSI was funded by an EU Marie Curie Research Training Grant (ERBFMBICT972700), E.T. and E.F. were funded by MEC grant MAR98-1417E and the EU contract CANIGO (MAS3CT960060). Funding for equipment and training for CR from the Royal Society is gratefully appreciated. This study was supported by the UK Natural Environmental Research Council through the Plymouth Marine Laboratory Core Strategic Research Programmes ‘‘Ocean Carbon Cycle Changes in the Coastal Zone’’ (OC4Z: 1999–2001) and ‘‘Microbially Driven Biogeochemical Cycles’’ (MDB: 2001–2006) and is MDB contribution number 56.

Dissolved organic carbon (DOC) production by microbial populations was measured at 19 stations in the Atlantic Ocean to quantify the fraction of photoassimilated carbon that flows through the dissolved organic pool at basin scale and to assess the relationship between the percentage of DOC production, phytoplankton size structure, and rates of net community production. Experiments were conducted during four cruises carried out between May 1998 and October 1999, covering three upwelling regions: Benguela (SW Africa), Mauritania (NW Africa) and NW Spain, and the oligotrophic North Atlantic subtropical gyre between 308N and 368N. Photic zone integrated particulate organic carbon (POC) production rates ranged from 10 to 1,178 mg C m 22 h 21 , thus covering a wide productivity spectrum. The percentage of DOC production with respect to total integrated primary production ranged from 4 to 42%, being larger in oligotrophic, picoplankton-dominated waters, where a balanced metabolism of the microbial community was observed, than in productive, net autotrophic waters, where large-sized cells formed the bulk of the phytoplankton biomass. A highly significant relationship was calculated between DOC and POC production rates in upwelling conditions. By contrast, the relationship between these variables in oligotrophic environments was weak, which suggests that different processes could be controlling the release of dissolved organic matter in productive and unproductive waters. Dissolved organic matter (DOM) is one of the least understood pools of marine matter and represents a major reservoir of organic carbon in the ocean. A large fraction of the dissolved organic carbon (DOC) present in the ocean ultimately derives from primary producers. However, a great deal of controversy still exists on the ecological significance and the ultimate control of DOC production in the ocean. The magnitude of DOC-related fluxes remains still largely uncertain, especially in oligotrophic regions. The high rates of DOC uptake by heterotrophic bacteria in relation to primary production recently measured in unproductive waters (e.g., Hansell et al. 1995; del Giorgio et al. 1997), largely justifies the growing biogeochemical interest of measuring and modeling DOC production in planktonic ecosystems. Initially, the radioactive carbon method for primary production estimation was modified for the measurement of direct excretion of dissolved organic compounds from algal cells. More recently, it has been recognized that several processes, besides direct excretion from intact algal cells, are 1

8 páginas, 2 tablas, 1 figura, The effect of solar radiation on dissolved organic matter (DOM) and the subsequent impact of photo-altered DOM on bacterial activity and community structure were assessed during two experiments in the coastal system of the Ría de Vigo (NW Iberian Peninsula). After exposure of 0.2 μm filtered seawater for 3.5 days to dark and full sunlight, an inoculum of the bacterial community collected at the same time as the exposed water was added and the mixture was incubated for 4 days in the dark at 15 °C. Changes in bacterial production (BP), diversity (assessed by Fluorescence in situ hybridization) and electron transport system (ETS) activity, dissolved organic carbon (DOC) and nitrogen (DON) and DOM humic-like absorption and fluorescence were followed. The exposure to sunlight had no effect on DOM concentrations while an average (±SD) decrease in DOM humic fluorescence of 45 ± 10% was found. The incubations with photo-altered DOM had lower BP (57 ± 11%), ETS (42 ± 9%) and bacterial carbon demand (BCD) (42 ± 8%) compared with the dark incubations, while bacterial growth efficiency (BGE) was unaffected. This suggests that DOM photo-alteration had a negative effect on bacterial metabolism in the study system. The bacterial growth on irradiated DOM resulted in a significant enrichment of the Gammaproteobacteria group compared with the dark control, indicating that solar exposure of DOM led to rapid changes in the bacterial community composition of the Ría de Vigo., This study was funded by fellowships to C.L from the early stage training site ECOSUMMER (MEST-CT-2004-020501) and the Carlsberg Foundation

10 pages, 5 figures, 2 tables, Although recognized as a potentially important source of both inorganic and organic nutrients, the impact of rainwater on microbial populations from marine planktonic systems has been poorly assessed. The effect of rainwater additions on bacterioplankton metabolism and community composition was evaluated in microcosm experiments enclosing natural marine plankton populations from the Ría de Vigo (NW Spain). The experiments were conducted during three different seasons (spring, autumn and winter) using rainwater collected at three different locations: marine, urban and rural sites. Bacterial abundance and production significantly increased up to 1.3 and 1.8-fold, respectively, after urban rainwater additions in spring, when ambient nutrient concentration was very low. Overall, the increments in bacterial production were higher than those in bacterial respiration, which implies that a higher proportion of carbon consumed by bacteria would be available to higher trophic levels. The response of the different bacterial groups to distinct rainwater types differed between seasons. The most responsive bacterial groups were Betaproteobacteria which significantly increased their abundance after urban (in spring and winter) and marine (in spring) rainwater additions, and Bacteroidetes which positively responded to all rainwater treatments in spring and to urban rainwater in autumn. Gammaproteobacteria and Roseobacter responded only to urban (in spring) and marine (in winter) rainwater treatment, respectively. The responses to rainwater additions were moderate and transient, and the resulting bacterial community structure was not importantly altered, This research was supported by the Xunta de Galicia through projects AddEx (grant PGIDIT06PXIB312222PR) and IMAN (grant 07MMA002402PR). S.M-G. was funded by a F. P. U. MEC fellowship. V.H-M. was funded by a F. P. I. MEC fellowship. E.T. was founded by a Ramón y Cajal-MEC contract

13 pages, 4 figures, 2 tables, The effects of inorganic and/or organic (glucose+AAs) inputs on phytoplankton and heterotrophic bacteria were assessed, using a microcosm approach, in two contrasting marine environments: an open ocean oligotrophic site (North Atlantic Subtropical Gyre) and a highly productive coastal embayment (Ría de Vigo, NW Spain). Overall, changes in microbial plankton biomass were smaller than those of metabolic rates. The largest increases in primary production, bacterial production and community respiration were measured in response to mixed () nutrient additions in both sites. Primary production responded to additions only in oligotrophic waters. The distinct autotrophic responses to nutrient additions measured in these environments were related to the different initial composition of phytoplankton populations and, presumably, also to differences in grazing pressures in both marine ecosystems. Heterotrophic bacteria were limited by organic substrates in both ecosystems, although mixed additions further enhanced bacterial growth in the subtropical gyre. The differences detected in bacterial responses to nutrient additions may be related to differences in nutrient limitations and to the prevalence of different relationships between components of the microbial food web (e.g. coupling between heterotrophic bacteria and phytoplankton and predation pressure) in both environments. We found a more relevant role of inorganic nutrients in controlling the efficiency of bacterial growth in oligotrophic regions as compared with highly productive systems. Our results suggest that organic matter inputs into both ecosystems might result in a tendency towards heterotrophy and in increases in bacterial growth efficiency. © 2013 Copyright Taylor and Francis Group, LLC., This research was supported by the Xunta de Galicia AddEx contract (PGIDIT06PXIB312222PR). S.M-G. was funded by a F. P. U. MEC fellowship. E.T. was funded by a Juan de la Cierva and a Ramo´n y Cajal-MEC contract

Proyectos RADIALES (IEO), REFORZA (PGIDIT06RMA60401PR)y HERCULES (09MMA027604PR)de la Xunta de Galicia y ANILE (CTM2009-08396) del Plan nacional de I+D+i, Long-term variability of phytoplankton biomass (chlorophyll a) and primary production (carbon fixation) in relation to changes in climatic and oceanographic factors was analysed for oceanic and shelf waters of the north and northwest Iberian Peninsula. Changes related to stratification in the water column and upwelling intensity were specifically addressed. The time series include measurements of primary production and biomass over 19 yr. Seasonally, the main mode of temporal variability of the series is the occurrence of phytoplankton blooms during the winter-spring and summer- autumn transition periods. On the northwestern coast (Galicia), the blooms are more frequent and attain higher biomass and production values than on the northern coast (Mar Cantábrico) due to the longer duration and higher intensity of upwelling in the former region. Even for the longest series there is no significant long-term trend in biomass, but primary production increased in Galicia and decreased in the Mar Cantábrico at nearly equivalent rates when considering monthly series. The lagged relationships between external factors and phytoplankton biomass and production suggest non-linear interactions between phytoplankton and climate. Neither the increase in surface stratification nor the decrease in upwelling intensity has negatively affected primary production in this region following consistent and systematic patterns. Changes in the amount and proportions of nutrients during winter water-mass formation, and an increased use of nutrients remineralised in situ, are proposed as the main causes of decadal variability in primary production in this region., Plan Nacional I+D+i, Xunta de Galicia, IEO

We investigated the effects of bottle enclosure on autotrophic and heterotrophic picoplankton in North and South subtropical Atlantic oligotrophic waters, where the biomass and metabolism of the microbial community are dominated by the picoplankton size class. We measured changes in both autotrophic ( Prochlorococcus , Synechococcus , and picoeukaryotes) and heterotrophic picoplankton biomass during three time series experiments and in 16 endpoint experiments over 24 h in light and dark treatments. Our results showed a divergent effect of bottle incubation on the autotrophic and heterotrophic components of the picoplankton community. The biomass of picophytoplankton showed, on average, a >50% decrease, mostly affecting the picoeukaryotes and, to a lesser extent, Prochlorococcus . In contrast, the biomass of heterotrophic bacteria remained constant or increased during the incubations. We also sampled 10 stations during a Lagrangian study in the North Atlantic subtropical gyre, which enabled us to compare the observed changes in the auto- to heterotrophic picoplankton biomass ratio (AB:HB ratio) inside the incubation bottles with those taking place in situ . While the AB:HB ratio in situ remained fairly constant during the Lagrangian study, it decreased significantly during the 24 h of incubation experiments. Thus, the rapid biomass changes observed in the incubations are artifacts resulting from bottle confinement and do not take place in natural conditions. Our results suggest that short (

As a first attempt to relate net nitrification rates with bacterial community structure in the coastal embayment of the Ría de Vigo (NW Spain), a set of 6 long-term (lasting 53 to 74 d) dissolved organic matter decomposition experiments were conducted in the dark and at a constant temperature of 15°C with surface seawater collected in January, February, April, and June 2008. Net nitrification rates were estimated from nitrate concentration changes. Evolution of bacterial community composition was followed using catalyzed reporter deposition-fluorescent in situ hybridization (CARD-FISH) and specific probes for 6 relevant bacterial groups, including Beta- and Gammaproteobacteria. The growth rates of Betaproteobacteria showed a significant linear positive relationship with nitrification rates that explained 82% of the observed variability, which strongly suggests that the main nitrifying microorganisms during the incubations belonged to the Beta subclass of Proteobacteria. A positive relationship was found between net nitrification rates and both ammonium (r2 = 0.92) and phosphate (r2 = 0.97) concentrations, which suggests a tight link among the nitrogen and phosphorus cycles, likely as a result of the role of phosphate as the bacterial growth-limiting nutrient.

Eleven culture experiments were conducted in the coastal upwelling ­system of the Ría de Vigo (NW Iberian Peninsula) by inoculating GF/C filtrated (10%) in 0.2 µm filtrated (90%) surface seawater collected under contrasting hydrographic conditions. Short-term (4 d) laboratory incubations were performed in the dark at 15°C. Dissolved organic carbon (DOC) concentration, bacterial biomass (BB), bacterial production (BP) and electron transport system (ETS) activity were then monitored to: (1) study the course of bacterial carbon demand (BCD) and growth efficiency (BGE) during the incubation period; and (2) determine how BCD and BGE were linked with changing environmental conditions. Following the 4 d incubation, BP decreased by, This study was funded by fellowships to C.L. from the early-stage training site ECOSUMMER (MESTCT-2004-020501) and the Carlsberg Foundation.

Atmospheric nutrient deposition into the open ocean increased over the past decades as a result of human activity and water-soluble organic nitrogen accounts for up to 30% of the total nitrogen inputs. The effects of inorganic and/or organic nutrient inputs on phytoplankton and heterotrophic bacteria have never been concurrently assessed in open ocean oligotrophic communities over a wide spatial gradient. We studied the effects of potentially limiting inorganic (nitrate, ammonium, phosphate, silica) and organic nutrient (glucose, aminoacids) inputs on microbial plankton biomass, community structure and metabolism in five microcosm experiments conducted along a latitudinal transect in the Atlantic Ocean (from 26° N to 29° S). Primary production rates increased up to 1.8-fold. Bacterial respiration and microbial community respiration increased up to 14.3 and 12.7-fold, respectively. Bacterial production and bacterial growth efficiency increased up to 58.8-fold and 2.5-fold, respectively. The largest increases were measured after mixed inorganic-organic nutrients additions. Changes in microbial plankton biomass were small as compared with those in metabolic rates. A north to south increase in the response of heterotrophic bacteria was observed, which could be related to a latitudinal gradient in phosphorus availability. Our results suggest that organic matter inputs associated with atmospheric deposition into the Atlantic Ocean will result in a predominantly heterotrophic versus autotrophic response and in increases in bacterial growth efficiency, particularly in the Southern Hemisphere. Subtle differences in the initial environmental and biological conditions are likely to result in differential microbial responses to inorganic and organic matter inputs.

15 páginas, 6 figuras, 4 tablas., We studied the effects of the Prestige oil spill on Ría de Vigo bacterial abundance, production and community structure by using mesocosms (ca. 3500 l) filled with water from the center of the Ría, to which we added a realistic concentration of polycyclic aromatic hydrocarbons (PAHs; initial concentrations of approximately 20 to 30 µg l–1 chrysene equivalents) at each of the 4 periods of the seasonal cycle: spring bloom, summer stratification, autumn upwelling and winter. We followed the changes in bacterial activity by leucine and thymidine incorporation, and the changes in bacterial assemblage structure by 16S rDNA DGGE. In addition, simultaneously with the winter mesocosm experiment, we ran microcosms with fuel additions equivalent to 0.5, 1, 2 and 4× the treatment imposed on the mesocosms in the seasonal experiments. Bacterial community structure was also analyzed by CARD-FISH. We detected significant effects of the PAHs on bacterial community structure (increased number of bands) and production only in the summer experiment. In the microcosm experiments, we found similar effects to those in the mesocosms at PAH concentrations of ca. 20 to 40 µg l–1, and clear detrimental effects on phytoplankton at concentrations of ca. 80 µg l–1, with large development of Gammaproteobacteria. Our results indicate that an oil spill of the Prestige’s magnitude will have effects on the microbial resident community only at certain times of the year, while at higher PAH concentrations the effects might be more evident. For most of the year, the resident Ría de Vigo microbial communities appear to be accustomed to PAH concentrations such as those used in these experiments., This work was supported by Project IMPRESION (VEM2003-20021). Financial support to I.L. and A.C.D. was provided by PhD fellowships from the Spanish government (MEC). Writing of the manuscript was supported by Project SUMMER (CTM2008-03309/MAR).

10 páginas, 4 tablas, 5 figuras, The degradation of dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) collected in the coastal upwelling system of the Ría de Vigo (NW Iberian Peninsula) was assessed following the time-course of DOC, DON and DOP concentrations in laboratory incubations. Initial concentrations varied from 73 to 94 µM for DOC, 4.5 to 7.2 µM for DON and 0.12 to 0.32 µM for DOP. The bioavailable fraction (BDOM) represented 17 ± 6% (average ± SE) of DOC, 38 ± 6% of DON and 65 ± 9% of DOP. BDOM was significantly correlated with temperature (R2 > 0.3, p < 0.05) and chlorophyll a (R2 > 0.5, p < 0.05), indicating that the differences in DOM bioavailability were associated with the seasonal variations in plankton biomass and activity. The C:N:P stoichiometry of BDOM, 111 (±38):18 (±6):1, was not significantly different from the Redfield ratio (106:16:1), pointing to a phytoplankton origin of BDOM. Accordingly, exponential rate constants of BDOM suggest that this pool is very labile. Despite the reduced flushing times of the Ría de Vigo, from 3 to 8 d, as much as 70 ± 13% of BDOC (average ± SD), 81 ± 8% of BDON and 88 ± 5% of BDOP are mineralized within the embayment. The remaining C-rich BDOM is exported to the adjacent oligotrophic waters, suggesting that the offshore transport of labile DOM must be accounted for when considering the carbon balance of ocean surface waters adjacent to productive coastal areas, This study was funded by a fellowship to C.L from the Early stage Training site ECOSUMMER (MEST-CT-2004-020501). Access to vessel time was provided by the RAFTING project (Impact of the mussel raft culture on the benthic-pelagic coupling in a Galician Ria, grant number: CTM2007-61983/MAR).

13 pages, 3 figures, 3 tables, Catalysed reported deposition-FISH and clone libraries indicated that Roseobacter, followed by Bacteroidetes, and some gammaproteobacterial groups such as SAR86, dominated the composition of bacterioplankton in Ría de Vigo, NW Spain, in detriment to SAR11 (almost absent in this upwelling ecosystem). Since we sampled four times during the year, we observed pronounced changes in the structure of each bacterioplankton component, particularly for the Roseobacter lineage. We suggest that such variations in the coastal upwelling ecosystem of Ría de Vigo were associated with the characteristic phytoplankton communities of the four different hydrographical situations: winter mixing, spring bloom, summer stratification, and autumn upwelling. We retrieved new sequences among the major marine bacterial lineages, particularly among Roseobacter, SAR11, and especially SAR86. The spring community was dominated by two Roseobacter clades that had previously been related to phytoplankton blooms. In the other seasons, communities with higher diversity than the spring one were detected, This research was supported by the project IMPRESION (VEM2003-20021) from the Spanish Ministerio de Ciencia e Innovación. J.A.-G. and I.L. thank the Ministerio de Ciencia e Innovación for their predoctoral fellowships and E.T. for her European Community Marie Curie Reintegration Fellowship (MERG-CT-2004-511937) and Juan de la Cierva-MEC contract

12 páginas, 3 tablas, 6 figuras, The aim of the present study was to correlate changes in dissolved organic matter (DOM) composition, as characterized through humic- and protein-like fluorescence, with changes in the abundance of major bacterial groups (Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Bacteroidetes) and bacterial activity in an upwelling system during the season of low productivity. Sampling was conducted under 2 contrasting periods characterized by low (February) and high (October) precipitation. In October, the mean humic-like DOM fluorescence in surface waters (3.1 ppb equivalents of quinine sulphate [ppb QS]) was higher than the annual average for this coastal zone (2.2 ppb QS), which was attributed to enhanced continental runoff. Alphaproteobacteria and Bacteroidetes were the most abundant groups, accounting for about 13 and 16% of total bacterial abundance, respectively. Betaproteobacteria were detectable only during the rainy period, accounting for 2 to 9% of total bacterial abundance. The bulk dissolved organic carbon concentration similarly explained the relative abundance of Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria (ca. 50% of total variability). By contrast, a strong correlation was found between the humic-like DOM fluorescence and the relative abundance of the Betaproteobacteria group, explaining 68% of the total variability. Multivariate linear regression analyses revealed that the relative abundance of Betaproteobacteria has the greatest influence on bacterial carbon fluxes, explaining 61 and 65% of bulk bacterial activity and biomass variability, respectively. Despite their relatively low abundance, Betaproteobacteria might play a relevant biogeochemical role in this coastal transition ecosystem during the low productivity period as allochthonous DOM consumers, This research was supported by the CICyT contract no. REN2003- 06633 (ZOTRACOS). E.T. was funded by a European Community Marie Curie Reintegration Fellowship (MERG-CT- 2004-511937) and a Juan de la Cierva-MEC contract.

13 pages, 7 figures, 2 tables.-- Available online Nov 17, 2008.-- Issue title: "The Atlantic Meridional Transect Progamme"., We present, test and implement two contrasting models to predict euphotic zone net community production (NCP), which are based on 14C primary production (PO14CP) to NCP relationships over two latitudinal (ca. 30°S–45°N) transects traversing highly productive and oligotrophic provinces of the Atlantic Ocean (NADR, CNRY, BENG, NAST-E, ETRA and SATL, Longhurst et al., 1995 [An estimation of global primary production in the ocean from satellite radiometer data. Journal of Plankton Research 17, 1245–1271]). The two models include similar ranges of PO14CP and community structure, but differ in the relative influence of allochthonous organic matter in the oligotrophic provinces. Both models were used to predict NCP from PO14CP measurements obtained during 11 local and three seasonal studies in the Atlantic, Pacific and Indian Oceans, and from satellite-derived estimates of PO14CP. Comparison of these NCP predictions with concurrent in situ measurements and geochemical estimates of NCP showed that geographic and annual patterns of NCP can only be predicted when the relative trophic importance of local vs. distant processes is similar in both modeled and predicted ecosystems. The system-dependent ability of our models to predict NCP seasonality suggests that trophic-level dynamics are stronger than differences in hydrodynamic regime, taxonomic composition and phytoplankton growth. The regional differences in the predictive power of both models confirm the existence of biogeographic differences in the scale of trophic dynamics, which impede the use of a single generalized equation to estimate global marine plankton NCP., This paper shows the potential of a systematic empirical approach to predict plankton NCP from local and satellite-derived P estimates., This work was supported by the NERC AMT programme (NER/O/S/2001/00680; this is contribution number 168. http://www.amt-uk.org) and the CYCIT project CIRCANA (MAR1999-1072-C03-01). P.S. was funded by EU Marie Curie Research Training and Return Grants and a MECD Contrato de Reincorporación, C.R. by a NERC Advanced Research Fellowship, E.T. and E.F. by MECD grants and the EU contract CANIGO (MAS3CT960060), and G.H.T. by an EU MAST fellowship.

10 páginas, 5 figuras, 1 tabla, Microbial degradation of dissolved organic matter (DOM) in planktonic ecosystems is carried out by diverse prokaryotic communities, whose growth rates and patterns of DOM utilization modulate carbon and nutrient biogeochemical cycles at local and global scales. Nine dilution experiments (September 2007 to June 2008) were conducted with surface water from the highly productive coastal upwelling system of the Ría de Vigo (NW Iberian Peninsula) to estimate bacterial growth rates of six relevant marine bacterial groups: Roseobacter, SAR11, Betaproteobacteria,Gammaproteobacteria, SAR86 and Bacteroidetes. Surprisingly, SAR11 dominated over the other bacterial groups in autumn, likely associated to the entry of nutrient-rich, DOC-poor Eastern North Atlantic Central Water (ENACW) into the embayment. Roseobacter and SAR11 showed significantly opposing growth characteristics. SAR11 consistently grows at low rates (range 0.19–0.71 day−1), while Roseobacter has a high growth potential (range 0.70–1.64 day−1). In contrast, Betaproteobacteria, Bacteroidetes, SAR86 and Gammaproteobacteria growth rates widely varied among experiments. Regardless of such temporal variability, mean SAR86 growth rate (range 0.1–1.4 day−1) was significantly lower than that of Gammaproteobacteria (range 0.3–2.1 day−1). Whereas the relative abundance of different bacterial groups showed strong correlations with several environmental variables, group-specific bacterial growth rates did not co-vary with ambient conditions. Our results suggest that different bacterial groups exhibit characteristic growth rates, and, consequently, distinct competitive abilities to succeed under contrasting environmental conditions, This study was funded by a fellowship to C.L. from the Early Stage Training site ECOSUMMER (MEST-CT-2004- 0205019). S.M.-G. was founded by a FPU-MEC fellowship. E.T. was founded by a Ramón y Cajal-MEC contract

12 páginas, 4 figuras, 1 tablas, We used mesocosm experiments to study the bacterioplankton community in a highly dynamic coastal ecosystem during four contrasting periods of the seasonal cycle: winter mixing, spring phytoplankton bloom, summer stratification and autumn upwelling. A correlation approach was used in order to measure the degree of coupling between the dynamics of major bacterial groups, heterotrophic carbon cycling and environmental factors. We used catalysed reporter deposition-fluorescence in situ hybridization to follow changes in the relative abundance of the most abundant groups of bacteria (Alphaproteobacteria, Gammaproteobacteria and Bacteroidetes). Bacterial carbon flux-related variables included bacterial standing stock, bacterial production and microbial respiration. The environmental factors included both, biotic variables such as chlorophyll-a concentration, primary production, phytoplankton extracellular release, and abiotic variables such as the concentration of dissolved inorganic and organic nutrients. Rapid shifts in the dominant bacterial groups occurred associated to environmental changes and bacterial bulk functions. An alternation between Alphaproteobacteria and Bacteroidetes was observed associated to different phytoplankton growth phases. The dominance of the group Bacteroidetes was related to high bacterial biomass and production. We found a significant, nonspurious, linkage between the relative abundances of major bacterial groups and bacterial carbon cycling. Our results suggest that bacteria belonging to these major groups could actually share a function in planktonic ecosystems, This research was supported by the MEC contract IMPRESION (VEM2003-20021). E.T. was funded by a European Community Marie Curie Reintegration Fellowship (MERG-CT-2004-511937) and a Juan de la Cierva-MEC contract

12 páginas, 3 tablas, 7 figuras, We used catalysed reported deposition – fluorescence in situ hybridization (CARD-FISH) to analyse changes in the abundance of the bacterial groups Alphaproteobacteria, Gammaproteobacteria and Bacteroidetes, and of hydrocarbon-degrading Cycloclasticus bacteria in mesocosms that had received polycyclic aromatic hydrocarbons (PAHs) additions. The effects of PAHs were assessed under four contrasting hydrographic conditions in the coastal upwelling system of the Rías Baixas: winter mixing, spring bloom, summer stratification and autumn upwelling. We used realistic additions of water soluble PAHs (approximately 20–30 μg l−1 equivalent of chrysene), but during the winter period we also investigated the effect of higher PAHs concentrations (10–80 μg l−1 chrysene) on the bacterial community using microcosms. The most significant change observed was a significant reduction (68 ± 5%) in the relative abundance of Alphaproteobacteria. The magnitude of the response of Cycloclasticus bacteria (positive with probe CYPU829) to PAHs additions varied depending on the initial environmental conditions, and on the initial concentration of added PAHs. Our results clearly show that bacteria of the Cycloclasticus group play a major role in low molecular weight PAHs biodegradation in this planktonic ecosystem. Their response was stronger in colder waters, when their background abundance was also higher. During the warm periods, the response of Cycloclasticus was limited, possibly due to both, a lower bioavailability of PAHs caused by abiotic factors (solar radiation, temperature), and by inorganic nutrient limitation of bacterial growth., This research was supported by the MEC contract IMPRESION (VEM2003-20021). E.T. was funded by an European Community Marie Curie Reintegration Fellowship (MERG-CT-2004-511937) and a Juan de la Cierva-MEC contract.

Marine Crenarchaeota are the most abundant single group of prokaryotes in the ocean, but their physiology and role in marine biogeochemical cycles are unknown. Recently, a member of this clade was isolated from a sea aquarium and shown to be capable of nitrification, tentatively suggesting that Crenarchaeota may play a role in the oceanic nitrogen cycle. We enriched a crenarchaeote from North Sea water and showed that its abundance, and not that of bacteria, correlates with ammonium oxidation to nitrite. A time series study in the North Sea revealed that the abundance of the gene encoding for the archaeal ammonia monooxygenase alfa subunit ( amoA ) is correlated with a decline in ammonium concentrations and with the abundance of Crenarchaeota. Remarkably, the archaeal amoA abundance was 1–2 orders of magnitude higher than those of bacterial nitrifiers, which are commonly thought to mediate the oxidation of ammonium to nitrite in marine environments. Analysis of Atlantic waters of the upper 1,000 m, where most of the ammonium regeneration and oxidation takes place, showed that crenarchaeotal amoA copy numbers are also 1–3 orders of magnitude higher than those of bacterial amoA . Our data thus suggest a major role for Archaea in oceanic nitrification.

The recently developed CARD-FISH protocol was refined for the detection of marine Archaea by replacing the lysozyme permeabilization treatment with proteinase K. This modification resulted in about twofold-higher detection rates for Archaea in deep waters. Using this method in combination with microautoradiography, we found that Archaea are more abundant than Bacteria (42% versus 32% of 4′,6′-diamidino-2-phenylindole counts) in the deep waters of the North Atlantic and that a larger fraction of Archaea than of Bacteria takes up l-aspartic acid (19% versus 10%). Over the past decade, our knowledge of the phylogenetic composition of marine prokaryotic communities, including those inhabiting the deep ocean, has increased considerably due to the application of molecular tools such as fingerprinting techniques, cloning, and sequencing (7, 9, 10, 12, 20, 21). Fluorescence in situ hybridization (FISH) can directly assess the abundance of specific prokaryotes, but it frequently yields a very low recovery of Bacteria and Archaea compared to the total number of 4′,6′-diamidino-2-phenylindole (DAPI)-stainable cells (3). Only recently, the use of polynucleotide probes allowed the assessment of the abundance of Bacteria and Archaea in the meso- and bathypelagic waters of the Pacific (18) and in Antarctic marine waters (5). These authors found that the relative abundance of Crenarchaea increased significantly with depth, comprising up to 39% of total picoplankton cells down to 500 m, whereas the abundance of Euryarchaea was very low (

The coupling of carbon and nitrogen fluxes between dissolved and particulate organic pools was examined at a coastal location off Galicia (northwest Spain). Monthly measurements of dissolved and particulate carbon and nitrogen stocks, along with inorganic carbon and nitrogen uptake and release of dissolved organic substances were obtained between October 1998 and September 1999. Carbon fluxes were determined using incubations of plankton with inorganic 14C and nitrogen fluxes were determined using incubations of plankton with 15N-ammonium. Dissolved organic carbon (DOC) was often released near the surface, while maximum release of dissolved organic nitrogen (DON) generally occurred near the base of the euphotic zone. Both rates were linearly related to the corresponding uptake rates; however, the percentages of extracellular release relative to total uptake (PER) were highest during low-productivity periods, when both carbon and nitrogen PER exceeded 50% in deep layers. PER values were generally below 20% near the surface. Despite maximum values of both DOC (0.63 µmol C l–1 h–1) and DON release (0.06 µmol N l–1 h–1) being measured during spring and summer, volumetric values of both rates were not significantly correlated through the year. Such a differential behaviour caused a mismatch between DOC:DON release ratios and the C:N ratios of seston at discrete depths. In contrast, euphotic-zone integrated release rates showed average DOC:DON ratios reflecting the C:N ratios of seston. These results suggest that most of the organic matter available for microbial plankton near the coast derives from phytoplankton, which in turn is sustained by a rapid recycling of organic matter when external nutrient inputs are reduced., 2

Seasonal variations in phytoplankton and bacterial biomass along with rates of primary production, dissolved organic carbon (DOC) release, bacterial production, dark respiration and vertical particle flux were determined from December 1998 to September 1999 at a coastal station off A Coruña (NW Spain) affected by episodes of wind-driven upwelling. Maximum phytoplankton biomass and production was associated with upwelling events. Bacterial biomass remained relatively constant throughout the study and was always lower than phytoplankton biomass. Depth-integrated rates of DOC release, which ranged from 0.2 to 3.1 gC m–2 d–1, were not a constant fraction of the total amount of carbon incorporated by primary producers. On average, DOC release accounted for 37 ± 7% of total primary production, and the highest values were measured during low-productivity periods. The supply of DOC by microplankton was globally sufficient to support the estimated bacterial activity, although a temporal shift between DOC release and bacterial consumption was observed. Primary production exceeded respiration during most of the seasonal study, with production/respiration ratios ranging from 1 to 7. The annual averaged daily net community production was 253 (±105) mmol O2m–2 d–1. The amount of particulate organic carbon exported from the euphotic layer was 1 to 86% of total primary production. The results of this study indicate that the coastal system is autotrophic, and suggest that most of the organic matter produced photosynthetically was channelled through the microbial food web. Xunta de Galicia; XUGA-10302B98 Instituto Español de Oceanografía; IEO-1007

11 pages, 9 figures, A knowledge of the balance between plankton gross primary production (GPP) and community respiration (CR)in the open ocean is vital to the accurate determination of the global carbon cycle, yet the paucity of open oceanmeasurements severely limits our understanding. This study measured GPP, net community production, dark CR,and size-fractionated primary production in the upper 200 m of a 12,100 km latitudinal (328S–488N) transect in theEastern Atlantic Ocean during May and June 1998. This comprehensive data set, which spans five contrastingplankton regimes, including two open ocean oligotrophic provinces, is used to derive a GPP : CR relationship, whichsuggests that net heterotrophy (GPP,CR) prevails in the eastern Atlantic when primary production falls below;100 mmol O2m22d21. The predictive capability of this relationship is compared with that of the only otherpublished relationship based on similar methodologies and is found to give a more representative description of theautotrophic (GPP.CR) to heterotrophic seasonal cycle in the Bay of Biscay. This improved predictive power isattributed to the increased representativeness of the current data set. Specifically, the interpretation suggests that theinfluence of community structure on net ecosystem metabolism implies that prediction of GPP : CR balances inpelagic ecosystems can be best achieved by use of a data set that covers a wide range of community structure andnot only a wide range in the magnitude of primary production

We used data collected at > 60 stations over a 10 yr period to build the carbon budget of the plankton community in the euphotic layer of the Eastern North Atlantic Subtropical Gyre (NASE). Autotrophic biomass exceeded microbial heterotrophic biomass by a factor of 1.7. Mean ( SE), integrated chlorophyll a concentration and net particulate primary production (PP) were 17 +/- 1 Mg m(2) and 271 +/- 29 mg C m(-2) d(-1), respectively. Protist grazing on phytoplankton represented > 90% of PP. Bacterial production (BP) was 17 +/- 3 mg C m(-2) d(-1). In vitro O-2-evolution experiments indicated that net community production was -65 +/- 16 mmolO(2) m(-2) d(-1), while community respiration (CR) averaged 124 +/- 13 mmolO(2) m(-2) d-1, equivalent to 1324 +/- 142 mg C m(-2) d(-1). However, the sum of the respiration rates by each microbial group, estimated from their biomass and metabolic rates, ranged from 402 to 848 Mg C m(-2) d-1. Therefore, CR could not be reconciled with the respiratory fluxes sustained by each microbial group. Comparison between estimated gross photosynthesis by phytoplankton (481 to 616 mg C m(-2) d-1) and the sum of respiration by each group suggests that the microbial community in the NASE province is close to metabolic balance, which would agree with the observed O-2 supersaturation in the euphotic layer. Taking into account the mean open-ocean values for PP, BP, CR and bacterial growth efficiency, we show that bacteria account for approximately 20% of CR. Our results suggest that the view that bacteria dominate carbon cycling in the unproductive ocean must be reconsidered, or else that in vitro incubations misrepresent the real metabolic rates of one or several microbial groups.

Contrasting hydrographic regimes were studied in the NW Iberian coastal transition zone in order to gain understanding of the relationship between planktonic community structure, production and loss rates, by concurrently measuring size-fractionated phytoplankton biomass and carbon incorporation as well as dissolved organic carbon production and dark respiration by micro- bial communities. Sampling was carried out in August 1998 and October 1999 at a series of stations representing vertical stratification and coastal upwelling conditions in summer, and vertical mixing and shelf-break poleward flow situations during the autumn. A close relationship was found between size-fractionated phytoplankton biomass and production, the relative allocation of total photosynthe- sis to dissolved and particulate organic carbon fractions, and the balance between production and respiration. Picoplankton-dominated communities showed net heterotrophic metabolism and were associated with relatively high rates of DOC production with respect to total carbon incorporation (>15%). In contrast, in coastal upwelling stations, where >2 µm cells dominated, less than 10% of total fixed carbon flowed to DOC, and the net metabolism of the microbial plankton community was autotrophic.

Rates of particulate organic carbon (POC) production, dissolved organic carbon (DOC) production and bacterial production were measured at 8 stations in the eastern North Atlantic Sub- tropical Gyre during August 1998. The euphotic-depth-integrated POC rate was on average 27 mgC m -2 h -1 . The corresponding averaged integrated DOC production rate was 5 mgC m -2 h -1 , i.e. about 20% of the total primary production. No statistically significant relationship was found between the rates of POC and DOC production, suggesting that other processes besides phytoplankton exudation, such as cell lysis or protist grazing, could be implied in the release of dissolved organic materials to the oceanic environment. Euphotic-depth-integrated bacterial biomass and production were on aver- age 214 mgC m -2 and 1.4 mgC m -2 h -1 , respectively. The lack of correlation between the rates of DOC release and bacterial activity and a bacterial carbon demand (BCD, calculated using an esti- mated bacterial growth efficiency ranging from 11 to 18%) in excess of DOC production suggested the existence of additional organic carbon sources (both allochthonous and/or autochthonous reser- voirs), apart from in situ phytoplankton-derived DOC production, for the maintenance of bacterial activity in this region during summer 1998. This uncoupling between phytoplankton and bacterio- plankton could partially explain the heterotrophic metabolic balance in this oligotrophic region during summer 1998.