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Analysis of seasonal patterns of marine bacterial community structure along horizontal and vertical spatial scales can help to predict long-term responses to climate change. Several recent studies have shown predictable seasonal reoccurrence of bacterial assemblages. However, only a few have assessed temporal variability over both horizontal and vertical spatial scales. Here we simultaneously studied the bacterial community structure at two different locations and depths in shelf waters of a coastal upwelling system during an annual cycle. The most noticeable biogeographic patterns observed were seasonality, horizontal homogeneity and spatial synchrony in bacterial diversity and community structure related with regional upwelling-downwelling dynamics. Water column mixing eventually disrupted bacterial community structure vertical heterogeneity. Our results are consistent with previous temporal studies of marine bacterioplankton in other temperate regions, and also suggest a marked influence of regional factors on the bacterial communities inhabiting this coastal upwelling system. Bacterial-mediated carbon fluxes in this productive region appear to be mainly controlled by community structure dynamics in surface waters, and local environmental factors at the base of the euphotic zone.

Article research, Microbial heterotrophic activity is a major process regulating the flux of dissolved organic matter (DOM) in the ocean, while the characteristics of this DOM strongly influence its microbial utilization and fate in the ocean. In order to broaden the vertical resolution of leucine-to-carbon conversion factors (CFs), needed for converting substrate incorporation into biomass production by heterotrophic bacteria, 20 dilution experiments were performed in the North Atlantic Ocean. We found a depth-stratification in empirical CFs values from epipelagic to bathypelagic waters (4.00 ± 1.09 to 0.10 ± 0.00 kg C mol Leu−1). Our results demonstrated that the customarily used theoretical CF of 1.55 kg C mol Leu−1 in oceanic samples can lead to an underestimation of prokaryotic heterotrophic production in epi- and mesopelagic waters, while it can overestimate it in the bathypelagic ocean. Pearson correlations showed that CFs were related not only to hydrographic variables such as temperature, but also to specific phylogenetic groups and DOM quality and quantity indices. Furthermore, a multiple linear regression model predicting CFs from relatively simple hydrographic and optical spectroscopic measurements was attempted. Taken together, our results suggest that differences in CFs throughout the water column are significantly connected to DOM, and also reflect differences linked to specific prokaryotic groups., 2,927

Oral communication Microbial heterotrophic activity is a major process regulating the flux of dissolved organic matter (DOM) in the ocean. DOM quantity and quality strongly influence its microbial utilization and fate in the ocean. In order to broaden the vertical resolution of leucine-to-carbon conversion factors (CFs), needed for converting substrate incorporation into biomass production by heterotrophic bacteria, nine dilution experiments were performed in the north Atlantic. We found a very consistent depth-stratification in empirical CFs values from epipelagic to bathypelagic waters (3.95 ± 0.05 to 0.90 ± 0.51 kg C mol Leu-1). Our results demonstrated that the customarily used CF of 1.55 kg C mol Leu-1 in oceanic waters leads to an underestimation of prokaryotic heterotrophic production in epi- and mesopelagic waters, while it causes a severe overestimation in bathypelagic waters. Pearson correlations showed that CFs were related not only to hydrographic variables but also to specific phylogenetic groups and DOM quality and quantity indicators. Furthermore, a multiple linear regression model predicting CFs from relatively simple hydrographic and optical spectroscopic measurements is provided. Taken together, our results suggest that differences in CFs throughout the water column might be mostly associated to the quality of DOM affecting the response of particular phylogenetic groups. ASLO

Oral communication The frequency of bushfires will enhance as a result of increasing occurrence of extreme heat and drought periods related to global warming. A fraction of the combusted matter generated during these episodes may reach coastal ecosystems while washed away by runoff waters. Nevertheless, the nature of this material and their ecological impact on the planktonic communities remains largely unknown. In this study, we investigated the impact of large fires that occurred in Galicia (NW of the Iberian Peninsula) in October 2017, with the aim of: a) chemically characterizing the materials produced during the event reaching the adjacent coastal areas and b) experimentally assessing the response of bacteria and phytoplankton to these episodic inputs. Significant increases in the concentrations of substances of pyrogenic origin, inorganic and organic nutrients together with an almost 6-fold increase in Chl a were measured at the stations located closest to the coast coinciding with the first strong rains after the fires. Ash addition experiments carried out in summer and winter showed a positive response of bacterial abundance (1.5-fold increase) and phytoplankton Chl a (2.6-fold increase) when these communities were limited by nutrients. No negative effects of the water-soluble fraction of ash were observed in any of the experiments conducted in this study. ASLO

Article, The capability of different bacterial populations to degrade abundant polymers, such as algal-derived polysaccharides, or to utilize prefentially polymers over monomers, remains largely unknown. In this study, microautoradiaography was combined with fluorescence in situ hybridization (MAR-FISH) to evaluate the ability of Bacterioidetes, SAR11, Roseobacter spp, Gammaproteobacteria and SAR86 cells to use bicarbonate, leucine and starch under natural light conditions at two locations in shelf surface waters off NW Spain. The percentage of cells incorporating bicarbonate was relatively high (mean 32% +- 4%) and was positively correlated with the intensity of solar radiation. The proportion of cells using starch (mean 56% +- 4%) or leucine (mean 47% +- 4%) was significantly higher than that using bicarbonate. On average, SAR11, Roseobacter spp and Gammaproteobacteria showed a similarly high percentage of cells using leucine (47%-65% of hybridized cells) than using starch (51%-64% of hybridized cells) while Bacteroidetes and SAR86 cells preferentially used starch (53% of hybridized cells) over leucine (34%-40% of hybridized cells). We suggest that the great percentage of bacteria using starch is related to a high ambient availability of polymers associated to algal cell lysis, which, in turn, weakens the short-term coupling between phytoplankton release and bacterial production., 5,843

Capítulo de libro, El conocimiento de la diversidad bacteriana en aguas marinas en Galicia es incipiente y se basa actualmente en el uso de técnicas de análisis molecular (secuenciación de un fragmento del gen ARNr 16S en aguas de ría, de plataforma, aguas oceánicas costeras, en playas y en sedimentos intermareales. La lista publicada incluye fundamentalmente géneros, debido a la imposibilidad de identificar con fiabilidad a nivel de especie basándose en esta técnica a partir de muestras oceánicas

Comunicación oral Bacterial biomass production is a key parameter for evaluating the role of bacterioplankton in ocean carbon cycling. However, bacterial production cannot be directly measured and is typically estimated from the incorporation rates of radiolabelled leucine. The conversion of leucine uptake rates into bacterial carbon production rates requires the use of conversion factors (CFs) which must be empirically determined. Despite the empirical leucine-to-carbon CFs vary widely across environments very little is known about its potential controlling factors. We conducted a set of 10 surface seawater cultures experiments where the growth of the natural bacterial assemblage was promoted by filtration (removal of grazers) or by both filtration and dilution. Sampling stations were located between 30 ºN and 30 ºS, including the Atlantic, Pacific and Indian oceans. CFs varied from 0.13 to 1.47 Kg C mol Leu-1, being higher in the filtrated than in the filtrated and diluted treatment. The abundance of picocyanobacteria explained 60% of the observed variability. Our results further suggest that the composition of bacterioplankton, as assessed by ARISA fingerprinting, may partially explain the observed variation in CFs.

Comunicación oral Recent studies in coastal waters suggest that phytoplankton is eventually limited or colimited by some metabolites derived from bacterial activity. The majority of phytoplankton species require an exogenous source of B12 vitamin for growth. As only selected prokaryotes are able to synthesize B12, they must be the ultimate source of B12 for auxotrophic phytoplankton. We conducted 3 microcosm experiments to assess the response of microbial plankton to B12-vitamin amendment in the coastal-ocean transition zone off NW Spain. Surface seawater was mixed with inorganic nutrients, B12-vitamin or a combination of both and incubated during 72h, under in situ temperature and light conditions. Size-fractionated (20, 3 and 0.2 μm) chlorophyll-a concentration and picoplankton abundance were monitored every 24h and changes in the size-fractionated eukaryotic and prokaryotic community structure were assessed by ARISA (automatic rRNA intergenic spacer analysis) at the end of the experiments. We observed that phytoplankton responded to B12-vitamin (alone or in combination) in 2 experiments. Nanophytoplankton was the most responsive fraction in terms of biomass, whereas changes in community structure associated to B12-vitamin addition were mainly observed for large eukaryotes.

Recent studies suggest that the dark ocean prokaryotes fix inorganic carbon at rates substantially higher than assumed. We have studied the contribution of Archaea vs. Bacteria to total prokaryotic fixation of dissolved inorganic carbon (DIC) in the meso- and upper bathypelagic waters of the world’s oceans during the Malaspina circumnavigation expedition carried out between December 2010 and July 2011. We used the metabolic inhibitor Erythromycin, an antibiotic specifically inhibiting growth of Bacteria but not affecting Archaea. Bacteria dominated throughout the water column in the three major ocean basins (54% of the total DAPI counts), decreasing in their relative contribution to total prokaryotic abundance from the surface to the meso- and bathypelagic waters. By contrast, the relative contribution of Thaumarchaeota was generally higher in the meso- and bathypelagic layers than in the surface waters (up to 29% of the total DAPI counts in the Pacific Ocean). Averaged over the entire water column, Thaumarchaeota contributed 8%, 33% and 18% to the total prokaryotic DIC fixation in the Indian, Pacific and Atlantic Ocean, respectively. The contribution of Thaumarchaeota to total prokaryotic DIC fixation increased with depth, particularly in the Atlantic below 1000 m depth and in the lower mesopelagic zone of the Pacific Ocean. Preliminary results from an station in the Atlantic Ocean, combining microautoradiography and fluorescence in situ hybridization (MICRO-CARD-FISH), confirmed that both Thaumarchaeota and some bacterial groups such as SAR 324 take up DIC. Thaumarchaeota and SAR 324 accounted for 7 % and 12% of DIC-positive DAPI-stained cells, respectively, as revealed by MICRO-CARD-FISH. Our results suggest that some phylogenetic groups may be significant contributors to the dark ocean chemoautotrophy.

Bacterial population distribution in the Mediterranean Sea has been mainly studied by considering small geographical areas or specific phylogenetic groups. The present study is a molecular microbiology investigation aimed to identify the environmental factors driving total bacterioplankton community composition of seawater samples collected along a transect covering the whole Mediterranean Sea. We performed automated ribosomal intergenic sequence analysis (ARISA) and microscope evaluation of prokaryotic abundance of seawater sampled across both vertical profiles and longitudinal transects in the whole basin. Prokaryotic abundance decreased with depth at all the stations and presented similar values in epi-, meso- and bathypelagic layers across the whole Mediterranean Sea. However, peculiar bacterial assemblages were selected along a longitudinal transect in the epipelagic layers of the eastern and western sub-basins. Vertical differences of the bacterial communities were observed only when considering the epi- and bathypelagic waters, while the study of the structure of bacterial communities at a finer scale across the water column displayed higher variability at the intermediate layers. Nonetheless, different physico-chemical factors were significantly related to the distribution of bacterial populations, both according to geographic position and down the water column in the whole Mediterranean Sea. These results demonstrated that bacterial assemblages are putatively correlated to different water masses of the complex hydrographical systems of the eastern and western Mediterranean sub-basins., 2

Esta obra ofrece una síntesis de la información recogida en las series temporales de observaciones oceánicas del IEO en la región atlántica del norte de España iniciadas en 1943 con el registro mareográfico; muestra evidencias de cambios interanuales en la física, la química y la biología del océano en relación con los factores climáticos, y estima los impactos más probables del clima en el océano futuro. Este volumen continúa la serie de estudios de la influencia del cambio climático en el mar iniciada con el Cambio climático en el Mediterráneo español (Vargas Yánez et al., 2010). En este caso, el enfoque es multidisciplinar, empleando, por primera vez, series de observaciones recogidas de forma coordinada y simultánea. A lo largo de sus ochos capítulos, se analiza la variabilidad climática atmosférica reciente y su influencia sobre las condiciones oceanográficas de la región, especialmente en relación con la intensidad y frecuencia del afloramiento de aguas profundas que determina, en gran medida, el aporte estacional de nutrientes a la superficie y, por tanto, la producción biológica. Se describen las tendencias en el nivel del mar a partir de las medidas de los mareógrafos de la zona con una estimación de los niveles extremos esperados a largo plazo. Se realiza un análisis comparativo –entre Galicia y el Cantábrico– de la variabilidad en los nutrientes inorgánicos y se determinan los elementos limitantes de la producción primaria en cada zona. Finalmente, se analizan las variaciones en las comunidades de fitoplancton, picoplancton y zooplancton como indicadoras de cambios en el ecosistema pelágico, destacando las fluctuaciones en la biomasa y producción primaria, base de la red trófica pelágica de la región, y la presencia de medusas y salpas y su relación con el clima. This book presents a synthesis of the oceanic time-series observations of IEO in the Atlantic region of northern Spain. These series, starting in 1943 with tide-gauges, reveal evidence of interanual changes in physical, chemical and biological properties of the ocean that were related to climatic factors, allowing to estimate future impacts of climate on the ocean. The volume continues the series started with “Climate Change in the Spanish Mediterranean” (Vargas Yánez et al., 2010). In this case the study is multidisciplinary, including for the first time series obtained in coordinated and simultaneous observational programs. The eight chapters first analyse recent climatic variability and its influence on the regional oceanography, particularly in relation to the intensity and frequency of the deep-water upwelling that largely determines the seasonal inputs of nutrients and primary production in this region. Next, the main trends in sea level revealed by tidal gauges along with the estimates of expected extreme levels are described. The variability in inorganic nutrients and the identification of limiting elements for primary production were presented as a comparative analysis between Galicia (in the West) and the Mar Cantábrico (in the east). Finally, the variability in the composition of the plankton communities, including phytoplankton, picoplankton and zooplankton, is analysed as indicative of changes in the pelagic ecosystem. Particular attention is given to the fluctuations in primary biomass and production and to the presence of salps and jellyfish in relation to climate. Versión del editor

Original research paper, 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) and a European Community Marie Curie Reintegration Fellowship (MERG-CT2004-511937) and a Juan de la Cierva-MEC contract., 2,393

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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., 1