Los aportes de aerosoles afectan las propiedades ópticas de la materia orgánica disuelta en las aguas costeras del Mediterráneo Noroccidental

10 pages, 6 figures, 1 table[EN] Aeolian inputs of organic and inorganic nutrients to the ocean are important as they can enhance biological production in surface waters, especially in oligotrophic areas like the Mediterranean. The Mediterranean littoral is particularly exposed to both anthropogenic and Saharan aerosol depositions on a more or less regular basis. During the last few decades experimental studies have been devoted to examining the effect of inorganic nutrient inputs from dust on microbial activity. In this study, we performed experiments at two different locations of the NW Mediterranean, where we evaluated the changes in the quality and quantity of dissolved organic matter due to atmospheric inputs of different origin (Saharan and anthropogenic) and its subsequent transformations mediated by microbial activities. In both experiments the humic-like and protein-like substances, and the fluorescence quantum yield increased after addition. In general, these changes in the quality of dissolved organic matter did not significantly affect the prokaryotes. The recalcitrant character of the fluorescent dissolved organic matter (FDOM) associated with aerosols was confirmed, as we found negligible utilization of chromophoric compounds over the experimental period. We framed these experiments within a two-year time series data set of atmospheric deposition and coastal surface water analyses. These observations showed that both Saharan and anthropogenic inputs induced changes in the quality of organic matter, increasing the proportion of FDOM substances. This increase was larger during Saharan dust events than in the absence of Saharan influence[ES] Los aportes atmosféricos de nutrientes orgánicos e inorgánicos al océano son importantes ya que pueden aumentar la producción biológica en aguas superficiales, especialmente en las zonas oligotróficas como el Mediterráneo. El litoral del Mediterráneo está particularmente expuesto a aportes de origen antropogénico y a deposiciones de polvo sahariano de forma más o menos regular. Durante las últimas décadas los estudios experimentales se han dedicado, sobre todo, a examinar el efecto de la entrada de nutrientes inorgánicos atmosféricos sobre la actividad microbiana. En este estudio, se realizaron experimentos con comunidades microbianas procedentes de dos zonas del Mediterráneo noroccidental. Se evaluaron los cambios en la calidad y cantidad de la materia orgánica disuelta debido a aportes atmosféricos de distinto origen y sus posteriores transformaciones mediadas por actividades microbianas. En ambos experimentos las sustancias orgánicas fluorescentes y el rendimiento cuántico de fluorescencia aumentaron después de la adición de material atmosférico. En general, estos cambios en la calidad de la materia orgánica no afectaron significativamente a los organismos procariotas. El carácter recalcitrante de la materia orgánica disuelta fluorescente (FDOM) contenida en los aerosoles se confirmó ya que la utilización de compuestos cromóforos durante el período experimental fue insignificante. Los resultados obtenidos se contextualizan en relación con una serie temporal de dos años de datos adquiridos de deposición atmosférica y análisis de agua superficial costera. La variabilidad temporal de estas dos variables mostró que tanto los aportes saharianos como antropogénicos provocaron cambios en la calidad de la materia orgánica disuelta en aguas superficiales, incrementando la fracción fluorescente. Éste aumento resultó ser mayor durante eventos de polvo sahariano que en ausencia de ellosThis study was supported by the projects 1179-1198. ADEPT (CTM2011-23458), DOREMI (CTM2012-342949) and ANIMA (CTM2015-65720-R MINECO/FEDER, UE). E.D. Sánchez-Pérez would like to thank the Consejo Nacional de Ciencia y Tecnologia (CONACyT) for their financial support through a PhD fellowship. I. Marín thanks the FPI Spanish scholarship programme for its support (BES 2012-052976)Peer Reviewe

Clases de tamaño, grupos quimiotaxonómicos y propiedades bio-ópticas del fitoplancton a lo largo de un transecto desde el mar Mediterráneo al SO del océano Atlántico

The relationships between the structure of the phytoplankton community and the bio-optical properties of surface waters were studied during the TransPEGASO cruise along a transect across the Atlantic Ocean that covered seven biogeographical provinces, from the Alborán Sea (SW Mediterranean) to the Patagonian Shelf. We characterized the composition of the phytoplankton community by means of high-performance liquid chromatography and CHEMTAX pigment analyses applied to whole water and two filtration size classes ( 0.5 mg m-3) with a single Mediterranean (MEDI) sample and those from the southwestern Atlantic Shelf (SWAS). According to CHEMTAX, the most important taxa in the tropical and subtropical Atlantic were Prochlorococcus, haptophytes and Synechoccoccus, while the MEDI and SWAS were dominated by diatoms and haptophytes. Both the VU and HI algorithms, which are based on pigment composition or Chl a concentration, predicted for SWAS a high proportion of nano- and microphytoplankton, while the SFF indicated dominance of the 0.5 mg m-3) con una sola muestra mediterránea (MEDI) y las de la plataforma patagónica, en el sudoeste del Atlántico (SWAS). Según CHEMTAX, los taxones más importantes en el Atlántico tropical y subtropical fueron Prochlorococcus, haptofitos y Synechoccoccus, mientras que las provincias MEDI y SWAS estuvieron dominadas por diatomeas y haptofitos. Tanto los algoritmos VU como los HI, que se basan en la composición de pigmentos o en la concentración de Chl a, predijeron para SWAS una alta proporción de nano y microfitoplancton, mientras que la SFF indicó un dominio de la clase de tamaño < 3 μm. Por otra parte, los resultados de CHEMTAX indicaron que, en promedio, la contribución de las diatomeas era importante en esta provincia. Sin embargo, en varias estaciones de SWAS para las que CHEMTAX estimaba una elevada contribución de diatomeas, las observaciones microscópicas encontraron solamente escasas concentraciones de células de diatomeas de tamaño nano- o microplanctónico. Esta discrepancia parece deberse a la presencia, confirmada por microscopía electrónica de barrido, de pequeñas células (< 3 μm) de la diatomea Minidiscus sp. y de Parmales (un grupo que comparte la composición pigmentaria con las diatomeas). Estos hallazgos advierten contra una asignación rutinaria de los pigmentos de las diatomeas a la clase de tamaño de microplancton. La absorción total (sin contar la propia del agua) en la columna de agua estuvo dominada por CDOM. En promedio, la contribución de la absorción de fitoplancton para las diferentes provincias osciló de 19.3% en MEDI a 45.7% en SWAS y 47% en la provincia del Atlántico Tropical Occidental (WTRA). La absorción del fitoplancton por unidad de Chl a [aph*(443), m2 mg-1] fue menor en MEDI y SWAS que en las provincias oligotróficas. aph*(443) se correlacionó negativamente con el primer componente derivado de un análisis de los componentes principales basado en la concentración de los pigmentos más importantes y no se correlacionó con indicadores de la estructura de tamaños de la comunidad fitoplanctónica tales como la proporción de Chl a en la clase < 3 μm o un índice de tamaño (SI) derivado de la distribución de clases de tamaño obtenida mediante el algoritmo VU. Estas observaciones indican que la variabilidad observada en aph*(443) se relacionaba principalmente con diferencias en la composición pigmentaria y posiblemente también con procesos de fotoaclimatación del fitoplancton, y que cualquier efecto de empaquetamiento debido al tamaño de las células quedaba probablemente enmascarado por otros factores. Este último resultado puede estar relacionado con una influencia relativamente pequeña del tamaño dentro del estrecho rango de concentraciones de Chl a considerado en nuestro estudio (todas eran ≤2.4 mg m-3)

Los aportes de aerosoles afectan las propiedades ópticas de la materia orgánica disuelta en las aguas costeras del Mediterráneo Noroccidental

Aeolian inputs of organic and inorganic nutrients to the ocean are important as they can enhance biological production in surface waters, especially in oligotrophic areas like the Mediterranean. The Mediterranean littoral is particularly exposed to both anthropogenic and Saharan aerosol depositions on a more or less regular basis. During the last few decades experimental studies have been devoted to examining the effect of inorganic nutrient inputs from dust on microbial activity. In this study, we performed experiments at two different locations of the NW Mediterranean, where we evaluated the changes in the quality and quantity of dissolved organic matter due to atmospheric inputs of different origin (Saharan and anthropogenic) and its subsequent transformations mediated by microbial activities. In both experiments the humic-like and protein-like substances, and the fluorescence quantum yield increased after addition. In general, these changes in the quality of dissolved organic matter did not significantly affect the prokaryotes. The recalcitrant character of the fluorescent dissolved organic matter (FDOM) associated with aerosols was confirmed, as we found negligible utilization of chromophoric compounds over the experimental period. We framed these experiments within a two-year time series data set of atmospheric deposition and coastal surface water analyses. These observations showed that both Saharan and anthropogenic inputs induced changes in the quality of organic matter, increasing the proportion of FDOM substances. This increase was larger during Saharan dust events than in the absence of Saharan influence.Los aportes atmosféricos de nutrientes orgánicos e inorgánicos al océano son importantes ya que pueden aumentar la producción biológica en aguas superficiales, especialmente en las zonas oligotróficas como el Mediterráneo. El litoral del Mediterráneo está particularmente expuesto a aportes de origen antropogénico y a deposiciones de polvo sahariano de forma más o menos regular. Durante las últimas décadas los estudios experimentales se han dedicado, sobre todo, a examinar el efecto de la entrada de nutrientes inorgánicos atmosféricos sobre la actividad microbiana. En este estudio, se realizaron experimentos con comunidades microbianas procedentes de dos zonas del Mediterráneo noroccidental. Se evaluaron los cambios en la calidad y cantidad de la materia orgánica disuelta debido a aportes atmosféricos de distinto origen y sus posteriores transformaciones mediadas por actividades microbianas. En ambos experimentos las sustancias orgánicas fluorescentes y el rendimiento cuántico de fluorescencia aumentaron después de la adición de material atmosférico. En general, estos cambios en la calidad de la materia orgánica no afectaron significativamente a los organismos procariotas. El carácter recalcitrante de la materia orgánica disuelta fluorescente (FDOM) contenida en los aerosoles se confirmó ya que la utilización de compuestos cromóforos durante el período experimental fue insignificante. Los resultados obtenidos se contextualizan en relación con una serie temporal de dos años de datos adquiridos de deposición atmosférica y análisis de agua superficial costera. La variabilidad temporal de estas dos variables mostró que tanto los aportes saharianos como antropogénicos provocaron cambios en la calidad de la materia orgánica disuelta en aguas superficiales, incrementando la fracción fluorescente. Éste aumento resultó ser mayor durante eventos de polvo sahariano que en ausencia de ellos

Assessing Viral Abundance and Community Composition in Four Contrasting Regions of the Southern Ocean

We explored how changes of viral abundance and community composition among four contrasting regions in the Southern Ocean relied on physicochemical and microbiological traits. During January–February 2015, we visited areas north and south of the South Orkney Islands (NSO and SSO) characterized by low temperature and salinity and high inorganic nutrient concentration, north of South Georgia Island (NSG) and west of Anvers Island (WA), which have relatively higher temperatures and lower inorganic nutrient concentrations. Surface viral abundance (VA) was highest in NSG (21.50 ± 10.70 × 106 viruses mL−1) and lowest in SSO (2.96 ± 1.48 × 106 viruses mL−1). VA was positively correlated with temperature, prokaryote abundance and prokaryotic heterotrophic production, chlorophyll a, diatoms, haptophytes, fluorescent organic matter, and isoprene concentration, and was negatively correlated with inorganic nutrients (NO3−, SiO42−, PO43−), and dimethyl sulfide (DMS) concentrations. Viral communities determined by randomly amplified polymorphic DNA–polymerase chain reaction (RAPD-PCR) were grouped according to the sampling location, being more similar within them than among regions. The first two axes of a canonical correspondence analysis, including physicochemical (temperature, salinity, inorganic nutrients—NO3−, SiO42−, and dimethyl sulfoniopropionate -DMSP- and isoprene concentrations) and microbiological (chlorophyll a, haptophytes and diatom, and prokaryote abundance and prokaryotic heterotrophic production) factors accounted for 62.9% of the variance. The first axis, temperature-related, accounted for 33.8%; the second one, salinity-related, accounted for 29.1%. Thus, different environmental situations likely select different hosts for viruses, leading to distinct viral communities.En prens

Sea Ice Microbiota in the Antarctic Peninsula Modulates Cloud-Relevant Sea Spray Aerosol Production

Este artículo contiene 21 páginas, 8 figuras.Sea spray aerosol (SSA) formation plays a major role in the climate system. The Antarctic Peninsula (AP) is affected by the greatest warming occurring in the Southern Ocean; changes in cryospheric and biological processes are being observed. Whilst there is some evidence that organic material produced by ice algae and/or phytoplankton in the high Arctic contributes to SSA, less is known about Antarctic Sea ice (sympagic) regions. To gain insight into the influence of Antarctic Sea ice biology and biogeochemistry on atmospheric aerosol, we report simultaneous water-air measurements made by means of in situ aerosol chamber experiments. For the first time, we present a methodology showing that the controlled plunging jet aerosol chamber settings do not cause major cell disruption on the studied sea ice ecosystems. Larger sea ice phytoplankton cells (>20 μm; mainly diatoms) tend to sediment at the bottomof the chamber (during the 24h experiment) and likely have a minor role on SSA production. When comparing four chamber experiments - we find that the two producing more SSA are the ones with highest abundance of nanophytoplankton cells (<20 μm; mainly nanoflagellates) as well as viruses. Our marine biogeochemical data show two broad groups of dissolved organic carbon: one rich in carbohydrates and proteic material and one rich in humic-like substances; the latter enhancing SSA production. This work provides unique insights into sea ice productivity that modulates SSA production, with potentially significant climate impacts. Further studies of these types are advised in order to see how microbiology impacts the biogeochemical cycling of elements and how aerosols are formed and processed in cold regions.The study was further supported by the Spanish Ministry of Economy through project PI-ICE (no. CTM 2017–89117-R) and the Ramon y Cajal fellowship (no. RYC-2012-11922). This work acknowledges the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). The National Centre for Atmospheric Science (NCAS) Birmingham group is funded by the UK Natural Environment Research Council. DOC was analyzed by Mara Abad (ICM-CSIC) and the POC was analyzed at the IIM-CSIC (Vigo).Peer reviewe

Application of chemotaxonomy to the study of the phytoplankton community structure in the Mediterranean Sea and in the Atlantic and Southern Oceans = Aplicación de la quimiotaxonomía al estudio de la estructura de la comunidad fitoplanctónica en el Mar Mediterráneo y en los oceános Atlántico y Antártico

[eng] Despite their small size, phytoplankton represents up to 50% of the global primary production of the Earth and serves as a connector between oceanic and atmospheric processes. Therefore, phytoplankton constitutes a central pillar in the comprehension of the cycles of mass and energy in the oceans. Their different attributes like size, abundance, community composition, functions, pigment complex and taxonomy provide relevant information to understand the processes of global change. In the past decades, the use of HPLC chromatography (High-Performance Liquid Chromatography) has proven as a very effective methodology to study marine phytoplankton. This technique, combined with the use of the statistic program CHEMTAX, allows to identify efficiently the contribution of certain taxonomic classes. This thesis is centered around the use of HPLC-CHEMTAX to identify the phytoplanktonic communities of three regions: the Mediterranean Sea, the Atlantic Ocean and the Antarctic Ocean, each characterized by different trophic conditions (from oligotrophic to eutrophic). With the results obtained, we expect to contribute to the comprehension of the local biochemical responses in a context of global change, as well as to improve future models of ecosystems and algorithms for remote sensing. To validate the data obtained, the results originated from the HPLC-CHEMOTAX were compared to other techniques used for identification and quantification, such as microscopy, flow cytometry and bio-optics. First, we focused on a temporal series (14 years) where we analyzed the seasonal and inter-annual dynamics of the phytoplanktonic community. We have verified that the phytoplanktonic community follows a seasonal pattern, just as had been observed in previous studies: diatoms dominated the blooms of late winter/early spring, while Synechococcus showed maximum abundances during the months of April and August. The cryptophytes and dinoflagellates showed a positive response to sporadic fertilization events, associated mainly to stormy events. In the next study of this thesis, we analyzed the size fractions obtained from sequential filtrations by HPLC-CHEMTAX (total, n+m>3 µm and pico3 µm y pico<3 µm) y comparamos los resultados obtenidos con los algoritmos propuestos por Vidussi et al. (2001), Uitz et al. (2006) e Hirata et al. (2011). Medimos el coeficiente específico de absorción del fitoplancton y se comparó con indicadores de tamaño. Finalmente, con la finalidad de describir la diversidad, abundancia y características fisiológicas de la comunidad fitoplanctónica en relación con la formación de aerosoles marinos, se ha utilizado el HPLC-CHEMTAX en el Océano Antártico Esta tesis prueba la eficacia del uso del HPLC-CHEMTAX para el estudio de las comunidades fitoplanctónicas en distintos procesos ecológicos y condiciones ambientales. Además, los resultados obtenidos demuestran que el HPLC-CHEMTAX es adecuado para cuantificar e identificar simultáneamente distintas clases de tamaño de fitoplancton

Aplicación de la quimiotaxonomía al estudio de la estructura de la comunidad fitoplanctónica en el Mar Mediterráneo y en los oceános Atlántico y Antártico

Memoria de tesis doctoral presentada por Sdena Oliveira Nunes para obtener el título de Doctora en Ciencias del Mar por la Universitat de Barcelona (UB), realizada bajo la dirección de la Dra. Marta Estrada i Miyares del Institut de Ciències del Mar (ICM-CSIC) y del Dr. Mikel Latasa Arcalís.-- 287 pages[EN] Despite their small size, phytoplankton represents up to 50% ofthe global primary production of the Earthand serves as a connector between oceanic and atmospheric processes. Therefore, phytoplankton constitutes a central pillar in the comprehension of the cycles of mass and energy in the oceans. Their different attributes like size, abundance, community composition, functions, pigment complex and taxonomy provide relevant information to understand the processes of global change. In the past decades, the use of HPLC chromatography (High-Performance Liquid Chromatography) has proven as a very effective methodology to study marine phytoplankton. This technique, combined with the use of the statistic program CHEMTAX, allows to identify efficiently the contribution of certain taxonomic classes. This thesis is centered around the use of HPLC-CHEMTAX to identify the phytoplanktonic communities of three regions: the Mediterranean Sea, the Atlantic Ocean and the Antarctic Ocean, each characterized by different trophic conditions (from oligotrophic to eutrophic). With the results obtained, we expect to contribute to the comprehension of the local biochemical responses in a context of global change, as well as to improve future models of ecosystems and algorithms for remote sensing. To validate the data obtained, the results originated from the HPLC-CHEMOTAX were compared to other techniques used for identification and quantification, such as microscopy, flow cytometry and bio-optics. First, we focused on a temporal series (14 years) where we analyzed the seasonal and inter-annual dynamics of the phytoplanktonic community. We have verified that the phytoplanktonic community follows a seasonal pattern, just as had been observed in previous studies: diatoms dominated the blooms of late winter/early spring, while Synechococcusshowed maximum abundances during the months of April and August. The cryptophytes and dinoflagellates showed a positive response to sporadic fertilization events, associated mainly to stormy events. In the next study of this thesis, we analyzed the size fractions obtained from sequential filtrations by HPLC-CHEMTAX(total, n+m>3 μm and pico3 μm y pico3 μm i pico<3 μm) i es van comparar els resultats obtinguts amb els algoritmes proposats per Vidussi et al. (2001), Uitz et al. (2006) i Hirata et al. (2011). També es va medir el coeficient específic d’absorció del fitoplàncton i es va comparar amb indicadors de tamany. Les nostres observacions suggereixen que els anàlisis de fraccionament poden informar sobre la estructura de mides de la comunitat, i que la variació del coeficient d’absorció del fitoplàncton està relacionat principalment amb la composició pigmentaria de les cèl·lules i amb els processos de fotoaclimatació en les diferents comunitats de fitoplàncton. Finalment, amb la finalitat de descriure la diversitat, abundància i característiques fisiològiques de la comunitat fitoplanctònica en relació amb la formació d’aerosols marins s’ha utilitzat el HPLC-CHEMTAX a l’Oceà Antàrtic. El nostre anàlisis destaca la associació de criptofites amb aigües superficials estratificades influenciades per la fusió del gel, la floració de diatomees a Georgia del Sud, una regió rica en ferro, així com la contribució substancial de formes menys estudiades de pelagophytes. En resum, aquesta tesis prova la eficàcia de l’ús del HPLC-CHEMTAX per a l’estudi de les comunitats fitoplanctòniques en diferents processos ecològics i condicions ambientals. A més, els resultats obtinguts demostren que el HPLC-CHEMTAX es adequat per quantificar i identificar simultàniament diferents classes de mides de fitoplànctonEsta tesis está encuadrada dentro del Programa de Doctorat de Ciencias de Mar de la Universidad de Barcelona y ha sido realzada en el Instituto de Ciencias del Mar –ICM dentro de Grups Consolidats de Recerca 2014 SGR/761 y 2014 SGR/1179 de la Generalitat de Catalunya y el proyecto PEGASO (CTM2012-37615) financiado por el Ministerio de la Economia y competitividad de España. Durante el periodo de elaboración de la tesis, la doctoranda ha disfrutado de una Beca Brasileña concedida por Council of Technological and Scientific Development (CNPq) of BrazilPeer Reviewe

Seasonal dynamics of the phytoplankton community in the Bay of Blanes, NW Mediterranean Sea

XXXII Trobades Científiques de la Mediterrània, Planeta Oceà - Planet Ocean, celebradas del 5 al 7 de octubre de 2016 en Maó, Menorca.-- Homenatge als Drs. Marta Estrada, Jordi Font i Jordi Salat, pioners de l'oceanografia mediterrània moderna. A tribute to Drs. Marta Estrada, Jordi Font and Jordi Salat, pioneers of modern Mediterranean oceanography.-- 1 pageThe seasonal variations of phytoplankton dynamics in surface waters of the Bay of Blanes (NW Mediterranean) were characterized during 14 years (2000 - 2014), based on biomarker pigment determinations. Pigment concentrations were determined by means of the HPLC method and the contribution of the main phytoplankton groups to total Chlorophyll a (Chla) was assessed through the application of the CHEMTAX (CHEMical TAXonomy) program. The most abundant phytoplankton groups were: Diatoms, prasinophytes, haptophytes >group 6+7>, haptophytes >group 8> and Synechococcus. Other detected groups were: core chlorophytes, dinoflagellates, cryptomonads, pelagophytes and Prochlorococcus. On average, diatoms dominated during some winter and spring months, and were abundant again in November. Prasinophytes presented the highest concentrations from December to March, decreased gradually between April and September, and increased again at the beginning of October. Synechococcus, which was practically absent during the winter period, was abundant between June and October, accounting for 39% of the total Chla in September. Haptophytes >group 6+7> showed their greatest concentration between April and October, while haptophytes >group 8> were more abundant in late autumn and winter. The variability of the phytoplankton community is discussed in relationship with the seasonal changes of environmental factors such as temperature, stratification and nutrient availability. The data showed also substantial interannual variation, highlighting the importance of time series for understanding coastal environment dynamics in a context of global changePeer Reviewe

Effect of Saharan dust on dynamics of nutrients and marine microbial plankton

Symposium on Integrating New Advances in Mediterranean Oceanography and Marine Biology, 26-29 November 2013, Institut de Ciències del Mar (CSIC), Barcelona, Catalunya, SpainThe Mediterranean Sea is a low-nutrient low-chlorophyll region, especially affected by aerosol deposition. The Sahara desert is considered the most important source of crustdominated aerosols in the world and to the Mediterranean basin, with the potential of providing essential nutrients for plankton growth. Previous amendment experiments with Saharan dust in seawater are not conclusive about the effects on the dynamics and composition of marine microorganisms. We performed an amendment experiment with aerosols of Saharan origin at realistic deposition rates, separating effects on bacteria from phytoplankton. Four containers were filled with 7.5 L of seawater (Barcelona, NW Mediterranean coastal water from 10 m depth) pre-meshed through 150 μm. Two of the containers were further filtered through 0.8 μm. The containers were incubated at 14 ºC with a 13:11 h light:dark cycle. At day 10, two of the containers were amended with 1.3 mg L-1 of Saharan dust (150D and 08D), while the two other served as controls (150K and 08K). Subsamples were taken daily for inorganic nutrients, chlorophyll a and flow cytometry determination. Results showed that 1 mg L-1 of dust produced an increase of 1.95 μmol L-1 of DIN, 4.49 μmol L-1 of SiO2 and 0.19 μmol L-1 of PO43- in container 150D, and 2.20 μmol L-1 of DIN, 4.61 μmol L-1 of SiO2 and 0.20 μmol L-1 of PO43- in 08D. Chlorophyll a concentration started to increase in 150D after the dust was added, reaching a concentration six times higher three days later. Autotrophic nanoeukaryotes and picoeukaryotes were mostly responsible for this increase, although Synechococcus cell abundance also increased in this container. Contrary, Synechococcus cell abundance showed a light decrease in 08D after the dust addition. In both containers, the total abundance of bacteria increased three days after the dust was added. However, the increase in 08D was larger than in the control. We conclude that Saharan dust affects phytoplankton abundance directly and has the potential to also affect bacteria directly. Effects on bacterial abundance may be delayed due to phytoplankton competition for nutrients or result from secondary stimulation owing to nutrient recycling. Further studies are needed to clarify the response under different initial conditionsPeer Reviewe

Seasonal and interannual variability of phytoplankton community structure in a Mediterranean coastal site

19 pages, 10 figures, 4 tables, supplementary material https://doi.org/10.3354/meps12493We studied phytoplankton community structure in surface waters of the fixed coastal station of the Blanes Bay Microbial Observatory (NW Mediterranean Sea). A chemotaxonomic approach based on HPLC analysis of phytoplankton pigments, followed by CHEMTAX algorithm implementation, was applied to a set of monthly samples taken during a 14 yr period (2000-2014). Additional samples were taken for nutrient analyses, flow cytometric measurements and during part of the period for phytoplankton cell counts by optical microscopy. Overall, the most abundant groups in terms of chlorophyll a (chl a) were haptophytes, diatoms and prasinophytes. In general, diatoms were the most important components of the total chl a maxima (T_Chl a). We observed a marked seasonality of T_Chl a and several phytoplankton groups (prasinophytes, diatoms, haptophytes, cryptophytes and pelagophytes) with autumn-winter or winter-spring maxima and summer minima, coinciding with similar variation in major nutrient concentrations. Prochlorococcus presented a fall-winter maximum and a spring-summer minimum, while Synechococcus peaked in April and August, and dinoflagellates were relatively important in summer. Superimposed to this general pattern, prasinophytes and diatoms responded positively to episodic fertilization events associated with freshwater runoff caused by rain storms. Most phytoplankton groups presented a decreasing linear interannual trend that could be associated with a reduction in nutrient availability. A possible driver for this oligotrophication is the improvement of wastewater treatment in the regionThe present study was supported in part by the project REMEI (CTM2015-70340-R, MINECO) as well as the Grups Consolidats de Recerca 2014 SGR/761 and 2014 SGR/1179 of the Generalitat de CatalunyaPeer reviewe