Prochlorococcus as a Possible Source for Transparent Exopolymer Particles (TEP)

Transparent exopolymer particles (TEP), usually associated with phytoplankton blooms, promote the formation of marine aggregates. Their exportation to deep waters is considered a key component of the biological carbon pump. Here, we explored the role of solar radiation and picocyanobacteria in the formation of TEP in oligotrophic surface waters of the Atlantic and Pacific Oceans in ten on-deck incubation experiments during the Malaspina 2010 Expedition. TEP concentrations were low on the ocean’s surface although these concentrations were significantly higher on the surface of the Pacific (24.45 ± 2.3 μg XG Eq. L-1) than on the surface of the Atlantic Ocean (8.18 ± 4.56 μg XG Eq. L-1). Solar radiation induced a significant production of TEP in the on-deck experiments from the surface water of the Pacific Ocean, reaching values up to 187.3 μg XG Eq. L-1 compared with the low production observed in the dark controls. By contrast, TEP production in the Atlantic Ocean experiments was lower, and its formation was not related to the light treatments. Prochlorococcus sp. from the surface ocean was very sensitive to solar radiation and experienced a high cell decay in the Pacific Ocean experiments. TEP production in the on-deck incubation experiments was closely related to the observed cell decay rates of Prochlorococcus sp., suggesting that this picocyanobacteria genus is a potential source of TEP. The evidence to propose such potential role was derived experimentally, using natural communities including the presence of several species and a variety of processes. Laboratory experiments with cultures of a non-axenic strain of Prochlorococcus marinus were then used to test TEP production by this genus. TEP concentrations in the culture increased with increasing cell abundance during the exponential phase, reaching the highest TEP concentration at the beginning of the stationary phase. The average TEP concentration of 1474 ± 226 μg XG Eq. L-1 (mean ± SE) observed at the stationary phase of P. marinus cultures is comparable with the values reported in the literature for diatom cultures, also growing in non-axenic as well as axenic cultures. Our results identify Prochlorococcus sp. as a possible relevant source of TEP in the oligotrophic ocean.This research was funded by the Expedición Malaspina 2010 project of the CONSOLIDER program (ref. CSD2008-00077), the project Stress-X (ref. CTM2012-32603) of the Spanish Minister of Economy and Competitiveness, and King Abdullah University of Science and Technology baseline funding to SA. FI was supported by a CSIC JAE-preDOC fellowship

Latitudinal changes of copepod egg production rates in Atlantic waters: Temperature and food availability as the main driving factors

Planktonic copepod abundance and egg production rates were determined in relation to temperature and chlorophyll concentration across a latitudinal transect in the Atlantic Ocean, ranging from 52"s to 24ON. Copepod distribution followed a pattern similar to that of chlorophyll a, with higher values at the southern latitudes. In contrast, egg production rates were significantly higher in the Atlantic intertropical zone, in the vicinity of the Equator. Copepod abundance was determined mainly by phytoplankton concentration, while rate processes (egg production rates) depended on chlorophyll a concentration and temperature. We propose multiple regression models including these 2 factors that explain up to 70% of the carbon specific egg production rates. The accuracy of these models versus previous ones including only temperature is also discussedhis study was financially supported by grant AMB94-0739 from the Spanish Interministerial Com- mission of Science and Technology (CICYT) to S A. and grants PN92-46651369 and EX96-46651369 from the Spanish Ministry of Universities and Research to A.C. IPeer reviewe

The percentage of living bacterial cells related to organic carbon release from senescent oceanic phytoplankton

© 2014 Author(s). Bacteria recycle vast amounts of organic carbon, playing key biogeochemical and ecological roles in the ocean. Bacterioplankton dynamics are expected to be dependent on phytoplankton primary production, but there is a high diversity of processes (e.g., sloppy feeding, cell exudation, viral lysis) involved in the transfer of primary production to dissolved organic carbon available to bacteria. Here, we show the percentage of living heterotrophic bacterioplankton in the subtropical NE Atlantic Ocean in relation to phytoplankton extracellular carbon release (PER). PER represents the fraction of primary production released as dissolved organic carbon. PER variability was explained by phytoplankton cell death, with communities experiencing higher phytoplankton cell mortality showing a larger proportion of phytoplankton extracellular carbon release. Both PER and the percentage of dead phytoplankton cells increased from eutrophic to oligotrophic waters, while abundance of heterotrophic bacteria was highest in the intermediate waters. The percentage of living heterotrophic bacterial cells (range: 60-95%) increased with increasing phytoplankton extracellular carbon release from productive to oligotrophic waters in the subtropical NE Atlantic. The lower PERs, observed at the upwelling waters, have resulted in a decrease in the flux of phytoplankton dissolved organic carbon (DOC) per bacterial cell. The results highlight phytoplankton cell death as a process influencing the flow of dissolved photosynthetic carbon in this region of the subtropical NE Atlantic Ocean, and suggest a close coupling between the fraction of primary production released and heterotrophic bacterial cell survival.This research is a contribution to the project RODA (CTM-2004-06842-CO3-O2) and to the project StressX (CTM2012-32603), funded by the Spanish Ministry of Economy and CompetitivenessPeer Reviewe

Large mesopelagic fishes biomass and trophic efficiency in the open ocean

Xabier Irigoien et al.With a current estimate of ~1,000 million tons, mesopelagic fishes likely dominate the world total fishes biomass. However, recent acoustic observations show that mesopelagic fishes biomass could be significantly larger than the current estimate. Here we combine modelling and a sensitivity analysis of the acoustic observations from the Malaspina 2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher. We show that there is a close relationship between the open ocean fishes biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fishes in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fishes in oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring ~10% of the primary production in deep waters.This research was conducted by the Malaspina 2010 Expedition project, funded by the Spanish Ministry of Economy and Competitiveness (Consolider-Ingenio 2010, CSD2008-00077). Additional financial support was provided by the Basque Country Government and by AZTI-TecnaliaPeer Reviewe

UV sensitivity of planktonic net community production in ocean surface waters

The net plankton community metabolism of oceanic surface waters is particularly important as it more directly affects the partial pressure of CO2 in surface waters and thus the air-sea fluxes of CO2. Plankton communities in surface waters are exposed to high irradiance that includes significant ultraviolet blue (UVB, 280-315 nm) radiation. UVB radiation affects both photosynthetic and respiration rates, increase plankton mortality rates, and other metabolic and chemical processes. Here we test the sensitivity of net community production (NCP) to UVB of planktonic communities in surface waters across contrasting regions of the ocean. We observed here that UVB radiation affects net plankton community production at the ocean surface, imposing a shift in NCP by, on average, 50% relative to the values measured when excluding partly UVB. Our results show that under full solar radiation, the metabolic balance shows the prevalence of net heterotrophic community production. The demonstration of an important effect of UVB radiation on NCP in surface waters presented here is of particular relevance in relation to the increased UVB radiation derived from the erosion of the stratospheric ozone layer. Our results encourage design future research to further our understanding of UVB effects on the metabolic balance of plankton communities. Key Points UV sensitivity of planktonic NCP ©2014. American Geophysical Union. All Rights Reserved.This research was funded by the projects RODA (CTM-2004-06842-CO3-O2) and ATOS (POL2006-00550/CTM), Humboldt-2009 project (CTM2008-02497-E), MEDEICG (CTM2009-07013), and the Malaspina-2010 expedition project funded by the CONSOLIDER Ingenio-2010 program (CSD2008-00077), all funded by the National Plan of R + D of the Spanish Ministry of Science and Innovation. A.R.d.G. was supported by the EU Marie Curie EST project Metaoceans (MEST-CT-2005-019678)Peer Reviewe

Evidences of Impacts of Climate Change on Mediterranean Biota

Spanish Ministry of Economy and Competitiveness (projects ESTRESX CTM2012-32603 and CLIMPACT CGL2014-54246-C2-1-R). Ramón y Cajal contract (RYC-2013-14714) funded by the Spanish Ministry of Economy and Competitiveness and the Regional Government of the Balearic Islands.Peer Reviewe

Size-dependence of volatile and semi-volatile organic carbon content in phytoplankton cells

The content of volatile and semivolatile organic compounds (VOC and SOC), measured as exchangeable dissolved organic carbon (EDOC), was quantified in 9 phytoplanktonic species that spanned 4 orders of magnitude in cell volume, by disrupting the cells and quantifying the gaseous organic carbon released. EDOC content varied 4 orders of magnitude, from 0.0015 to 14.12 pg C cell−1 in the species studied and increased linearly with increasing phytoplankton cell volume following the equation EDOC (pg C cell−1) = −2.35 × cellular volume (CV, μm3 cell−1) 0.90 (± 0.3), with a slope (0.90) not different from 1 indicating a constant increase in volatile carbon as the cell size of phytoplankton increased. The percentage of EDOC relative to total cellular carbon was small but varied 20 fold from 0.28 to 5.17%, and no obvious taxonomic pattern in the content of EDOC was appreciable for the species tested. The cell release rate of EDOC is small compared to the amount of carbon in the cell and difficult to capture. Nonetheless, the results point to a potentialf flux of volatile and semivolatile phytoplankton-derived organic carbon to the atmosphere that has been largely underestimated and deserves further attention in the future.This is a contribution to the “Malaspina 2010” COSOLIDER project funded by the Spanish Ministry of Science and Innovation (CSD2008-00077).Peer reviewedPeer Reviewe

Die rußländische Sicherheitspolitik um die Jahrtausendwende

13 pages, 3 figures, 6 tablesThe metabolic carbon requirements and excretion rates of three major zooplankton groups in the Southern Ocean were studied in the vicinity of the Antarctic Peninsula in February 2009. The research was conducted in the framework of the ATOS project (POL2006-00550/CTM), as part of the Spanish contribution to the International Polar Year. Our objective was to ascertain the possible consequences of changes on size spectrum and community structure of the Southern Ocean zooplankton for the cycling of biogenic carbon and the stoichiometry of dissolved inorganic nutrients. The carbon respiratory demands and NH4-N and PO4-P excretion rates of < 5 mm size copepods, krill (represented by furcilia spp. and adult Euphausia superba) and salps (blastozoids of Salpa thompsoni) were estimated by incubation experiments. The respiration rates and N:P metabolic quotients of salps were more than twice those of krill (furcilia spp. and adults) and copepods. The possible community shift from krill to salps in the Southern Ocean would therefore encompass not only the substitution of a pivotal zooplankton group (krill) by one with an apparently indifferent role in Antarctic food webs and with higher specific metabolic carbon demands (salps), but the changes in the proportion of zooplankton-recycled N and P would modify the N:P stoichiometry of the dissolved nutrient pool, thus inducing changes in the functional and structural properties of phytoplankton that would translate to the whole Southern Ocean ecosystemThis work was supported by the Spanish funded projects ATOS (POL 2006-0550/CTM) to Carlos M. Duarte, PERFIL (CTM 2006-12344-C01) to Miquel Alcaraz, and the UE funded project ATP (www.eu-atp.org) contract # 226248 to P. WassmannPeer Reviewe

Temporal evolution of temperatures in the Red Sea and the Gulf of Aden based on in situ observations (1958–2017)

The Red Sea holds one of the most diverse marine ecosystems in the world, although fragile and vulnerable to ocean warming. Several studies have analysed the spatio-temporal evolution of temperature in the Red Sea using satellite data, thus focusing only on the surface layer and covering the last ∼30 years. To better understand the long-term variability and trends of temperature in the whole water column, we produce a 3-D gridded temperature product (TEMPERSEA) for the period 1958–2017, based on a large number of in situ observations, covering the Red Sea and the Gulf of Aden. After a specific quality control, a mapping algorithm based on optimal interpolation have been applied to homogenize the data. Also, an estimate of the uncertainties of the product has been generated. The calibration of the algorithm and the uncertainty computation has been done through sensitivity experiments based on synthetic data from a realistic numerical simulation. TEMPERSEA has been compared to satellite observations of sea surface temperature for the period 1981–2017, showing good agreement especially in those periods when a reasonable number of observations were available. Also, very good agreement has been found between air temperatures and reconstructed sea temperatures in the upper 100 m for the whole period 1958–2017, enhancing confidence in the quality of the product. The product has been used to characterize the spatio-temporal variability of the temperature field in the Red Sea and the Gulf of Aden at different timescales (seasonal, interannual and multidecadal). Clear differences have been found between the two regions suggesting that the Red Sea variability is mainly driven by air–sea interactions, while in the Gulf of Aden the lateral advection of water plays a relevant role. Regarding long-term evolution, our results show only positive trends above 40 m depth, with maximum trends of 0.045 + 0.016 ∘C decade−1 at 15 m, and the largest negative trends at 125 m (−0.072+0.011 ∘C decade−1). Multidecadal variations have a strong impact on the trend computation and restricting them to the last 30–40 years of data can bias high the trend estimates.En prensa2,29

Phototoxic effects of PAH and UVA exposure on molecular responses and developmental success in coral larvae

Exposure to polycyclic aromatic carbons (PAHs) poses a growing risk to coral reefs due to increasing shipping and petroleum extraction in tropical waters. Damaging effects of specific PAHs can be further enhanced by the presence of ultraviolet radiation, known as phototoxicity. We tested phototoxic effects of the PAHs anthracene and phenanthrene on larvae of the scleractinian coral Acropora tenuis in the presence and absence of UVA (320–400 nm). Activity of superoxide dismutase (SOD) enzyme was reduced by anthracene while phenanthrene and UVA exposure did not have any effect. Gene expression of MnSod remained constant across all treatments. The genes Catalase, Hsp70 and Hsp90 showed increased expression levels in larvae exposed to anthracene, but not phenanthrene. Gene expression of p53 was upregulated in the presence of UVA, but downregulated when exposed to PAHs. The influence on stress-related biochemical pathways and gene expresson in A. tenuis larvae was considerably greater for anthracene than phenanthrene, and UVA-induced phototoxicity was only evident for anthracene. The combined effects of UVA and PAH exposure on larval survival and metamorphosis paralleled the sub-lethal stress responses, clearly highlighting the interaction of UVA on anthracene toxicity and ultimately the coral's development