Bacterial carbon demand and growth efficiency in a coastal upwelling system

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 <4 times its initial values (range from 3 to 11 times) and ETS activity increased by 6 times its initial values (range from 1 to 75 times). As a result, BCD increased by 5 times (range from 1 to 16 times) and the BGE decreased by 15 times (range from 2 to 55 times) over the same period. BGE integrated over the 4 d incubation period ranged from 7 ± 1% to 55 ± 11% (mean ± SD: 27 ± 15%); integrated BGE increased significantly (R2 = 0.64, p < 0.003) with the initial concentration of dissolved inorganic nitrogen (DIN), and decreased significantly (R2 = 0.55, p < 0.01) with the C:N ratio of the bioavailable dissolved organic matter (BDOM). A multiple linear regression with DIN and the C:N ratio of BDOM explained 89% of the observed variability in the integrated BGE, demonstrating the strong dependence of growth efficiency on nutrient conditions and the quality of the organic substrate feeding the community of this coastal embayment.This study was funded by fellowships to C.L. from the early-stage training site ECOSUMMER (MESTCT-2004-020501) and the Carlsberg Foundation.Peer reviewe

Microbial and photochemical reactivity of fluorescent dissolved organic matter in a coastal upwelling system

Original research articleWe observed significant changes in the dissolved oxygen content and the fluorescence of humic substances anddissolved aromatic amino acids after 24 h light and dark incubations in the coastal upwelling system of the Rı´a deVigo under a wide variety of meteorologic and oceanographic conditions. Respiration rates were inverselycorrelated with the net production of humic fluorescence in the dark at a net rate of 20.027 6 0.003 mgequivalents of quinine sulphate per mmol of O2, suggesting that marine humics are a by-product of the bacterialrespiration of dissolved organic matter (DOM). On the contrary, humic fluorescence consumption in the lightminus dark incubations was positively correlated with the net production in the dark, indicating a rapidphotodegradation of recently produced marine humic substances. Parallel incubation experiments demonstratedthat daily photodegradation rates and residual humic fluorescence levels followed a seasonal pattern characterizedby a marked autumn maximum. Finally, a significant linear correlation between the gross primary production(Pg) and the net production of aromatic amino acids fluorescence in the light pointed to the rapid consumption ofdissolved protein-like materials at a net average rate of 21.4 6 0.2 ppb equivalents of tryptophan per day, whichaccumulates in the water column only when Pg exceeds 80 6 20 mmol kg21d21Financial support came from the Spanish Ministerio de Cienciay Tecnologı´a (MCyT) grant REN2000-0880-C02-01 and Xunta deGalicia grant PGIDT01MAR40201PN and a fellowship from theMCyT and the I3P-CSIC ProgramVersión del editor3,38

Effects of the photochemical transformation of dissolved organic matter on bacterial physiology and diversity in a coastal system

8 páginas, 2 tablas, 1 figuraThe 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 FoundationPeer reviewe

Phytoplankton diversity effect on ecosystem functioning in a coastal upwelling system.

This work is part of the time series project RADIALES conducted and funded by the Instituto Español de Oceanografía (http://www.seriestemporales-ieo.net) with additional support from project MarRisk (Interreg POCTEP Spain-Portugal) grant number 0262 MARRISK 1 E, from grants Contrato-Programa GAIN-IEO, and grant number IN607A2018/2 of the Axencia Galega de Innovación (GAIN, Xunta de Galicia, Spain). JO was supported by a Junta para la Ampliación de Estudios Fellowship (JAE-Doc programme 2011) from the CSIC and ESF.Species composition plays a key role in ecosystem functioning. Theoretical, experimental and field studies show positive effects of biological diversity (biodiversity) on ecosystem processes. However, this link can differs between taxonomic and functional diversity components and also across trophic levels. These relationships It haves been hardly studied in planktonic communities occurring inof coastal upwelling systems. Using a 28 yr time series of phytoplankton and zooplankton assemblages we examined the effects of phytoplankton diversity on resource use efficiency at the two trophic levels (RUE, ratio of biomass to limiting resource) in the Galician upwelling system (NW Iberian peninsula). Fitting Generalized Least Squares models we show that phytoplankton diversity was the best predictor for RUE across planktonic trophic levels. This link varied depending on the biodiversity component considered: while the effect of phytoplankton richness on RUE was positive for phytoplankton RUE and negative for zooplankton RUE, phytoplankton evenness effect was negative for phytoplankton RUE and positive for zooplankton RUE. Overall, taxonomic diversity had higher explanatory power than functional diversity, and variability in phytoplankton and zooplankton RUE decreased with increasing phytoplankton taxonomic diversity. Phytoplankton used resources more efficiently in warmer waters and at greater upwelling intensity although these effects were not as strong as those for biodiversity. These results suggest that phytoplankton species numbers in highly dynamic upwelling systems are important for maintaining the planktonic biomass production leading us to hypothesize the relevance of likely through complementarity effects. However, we further postulate that a selection effect may operate also because assemblages with low evenness were dominated by diatoms with specific functional traits increasing their ability to exploit resources more efficiently.This work is part of the time series project RADIALES conducted and funded by the Instituto Español de Oceanografía (http://www.seriestemporales-ieo.net) with additional support from project MarRisk (Interreg POCTEP Spain-Portugal) grant number 0262 MARRISK 1 E, from grants Contrato-Programa GAIN-IEO, and grant number IN607A2018/2 of the Axencia Galega de Innovación (GAIN, Xunta de Galicia, Spain). JO was supported by a Junta para la Ampliación de Estudios Fellowship (JAE-Doc programme 2011) from the CSIC and ESF.Versión del edito

Solar irradiance dictates settlement timing and intensity of marine mussels

11 páginas, 4 figuras, 2 tablas.-- This work is licensed under a Creative Commons Attribution 4.0 International LicenseIdentifying the environmental factors driving larval settlement processes is crucial to understand the population dynamics of marine invertebrates. This work aims to go a step ahead and predict larval presence and intensity. For this purpose we consider the influence of solar irradiance, wind regime and continental runoff on the settlement processes. For the first time, we conducted a 5-years weekly monitoring of Mytilus galloprovincialis settlement on artificial suspended substrates, which allowed us to search for interannual variability in the settlement patterns. Comparison between the seasonal pattern of larval settlement and solar irradiance, as well as the well-known effect of solar irradiance on water temperature and food availability, suggest that solar irradiance indirectly influences the settlement process, and support the use of this meteorological variable to predict settlement occurrence. Our results show that solar irradiance allows predicting the beginning and end of the settlement cycle a month in advance: Particularly we have observed that solar irradiance during late winter indirectly drives the timing and intensity of the settlement onset, Finally, a functional generalise additive model, which considers the influence of solar irradiance and continental runoff on the settlement process, provides an accurate prediction of settlement intensity a fortnight in advanceThis study was funded by PROINSA-CSIC contract-project (CSIC0704101100001), CSIC- PIE project (CSIC 201540E107) and EU H2020 project ClimeFish (EU 677039).Peer reviewe

Local remineralization patterns in the mesopelagic zone of the Eastern North Atlantic, off the NW Iberian Peninsula

Original research articleThe short-time-scale variability of the remineralization patterns in the domain of Eastern North Atlantic Central Waters (ENACW) off the NW Iberian Peninsula is studied based on biogeochemical data (oxygen, nutrient salts, total alkalinity, pH, dissolved organic matter and fluorescence of dissolved humic substances) collected weekly between May 2001 and April 2002. The temporal variability of inorganic variables points to an intensification of remineralization during the summer and autumn, with an increase of nutrients, total inorganic carbon and fluorescence and a decrease of oxygen. During the subsequent winter mixing, there is a biogeochemical reset of the system, with lower nutrients, total inorganic carbon and fluorescence and higher oxygen. In contrast to inorganic variables, the levels of dissolved organic matter in the ENACW seem to respond to short-term events probably associated with fast sinking particles, where solubilisation of organic matter prevails over remineralization. Applying a previously published stoichiometric model, we observed a vertical fractionation of organic-matter remineralization. Although there is a preferential remineralization of proteins and P compounds in the entire domain of ENACW, the percentage was higher in the upper ENACW (σ80% for the upper ENACW and 63% for the lower. Likewise, the redissolution of calcareous structures contributes about 6% and 13% to the carbon regenerated in the upper and lower layers of ENACW, respectively.Financial support for this work came from CICYT project MAR99-1039-C02-01; a contract of the Ramón y Cajal programme of the Spanish MCYT and a fellowship from the Spanish MCYT.Versión del edito

Coupling between the Iberian basin–scale circulation and the Portugal boundary current system. A chemical study

15 páginas, 7 figurasThe role played by the Portugal Current System in the ventilation of the different modes of Eastern North Atlantic Central Water (ENACW) is evaluated with data from a series of cruises carried out along the western coast of the Iberian Peninsula. Results show the Portugal Current, located west of 10.3°W, conveying fresh modes of recently ventilated ENACW of subpolar origin to the south. Within 70 km of the slope, the Portugal Coastal Countercurrent transports northwards low oxygen/high nutrient ENACW of subtropical origin. Downstream ventilation of ENACW of subtropical origin occurs by mixing or entrainment with offshore ventilated ENACW. We point to mesoscale eddies as the main mechanism for this downstream indirect ventilation, which reconciles opposing views from direct current measurements and hydrographic studies.Financial support for this work came from the EU, contract No. MAS2-CT93-65, and the Spanish CICYT, Contract No. AMB93-1415-CE.Peer reviewe

Contrasting complexing capacity of dissolved organic matter produced during the onset, development and decay of a simulated bloom of the marine diatom Skeletonema costatum

Original research articleThe capacity of natural dissolved organic matter (DOM) produced during the onset, development and decay of a simulated bloom of the marine diatom Skeletonema costatum to complex free copper has been followed for a 2 week period. Copper binding capacity of the culture was measured by anodic stripping voltammetry (ASV) with a hanging mercury drop electrode (HMDE). The concentration of dissolved organic carbon (DOC) and two fluorophores, M (humic-like, Ex/Em: 320 nm/410 nm) and T (protein-like, Ex/Em: 280 nm/350 nm), were followed during the course of the incubation. Models using DOC concentrations alone could not accurately predict the complexing capacity of the culture, especially at the end of the bloom, and better predictions were obtained when fluorescence measurements were considered. They were helpful in characterising two types of copper ligands produced in the culture. The first type, traced by the fluorescence of peak T, was related to labile DOC directly exuded by phytoplankton. The second type, traced by the fluorescence of peak M, was the refractory humic-like material presumably produced in situ as a by-product of the bacterial degradation of phytogenic materials. During the onset and development of the bloom (days 0 to 7), the fluorescence of peak T explains 60–80% of the total complexing capacity of the culture, suggesting that exuded “protein-like” compounds among other exuded complexing agents efficiently complexed free copper. On the contrary, during the decay (days 8 to 13), these ligands were replaced by humic substances as the complexing agent for copper.Financial support for this work came from the Spanish ‘Ministerio de Educación y Ciencia’ (MEC), Grant Nos. REN2000-0880-C02-01 MAR and REN2003-00958 MAR and the ‘Xunta de Galicia’, Grant No. PGIDT01MAR40201PN.Versión del editor2,75

Effect of dissolved organic matter (DOM) of contrasting origins on Cu and Pb speciation and toxicity to Paracentrotus lividus larvae

4 tablas, 6 figurasWater samples of contrasting origin, including natural seawater, two sediment elutriates and sewage-influenced seawater, were collected and obtained to examine the effect of the dissolvedorganicmatter (DOM) present on metal bioavailability. The carbon content (DOC) and the optical properties (absorbance and fluorescence) of the coloured DOM fraction (CDOM) of these materials were determined. Cu and Pb complexation properties were measured by anodic stripping voltammetry (ASV) and the effect of DOM on Cu and Pb bioavailability was studied by means of the Paracentrotus lividus embryo-larval bioassay. Sediment elutriates and sewage-influenced water (1) were enriched 1.4–1.7 times in DOC; (2) absorbed and reemitted more light; and (3) presented higher Cu complexation capacities (LCu) than the natural seawater used for their preparation. LCu varied from 0.08 μM in natural seawater to 0.3 and 0.5 μM in sediment elutriates and sewage-influenced water, respectively. Differences in DOC, CDOM and Cu complexation capacities were reflected in Cu toxicity. DOM enriched samples presented a Cu EC50 of 0.64 μM, significantly higher than the Cu EC50 of natural and artificial seawater, which was 0.38 μM. The protecting effect of DOM on Cu toxicity greatly disappeared when the samples were irradiated with high intensity UV-light. Cu toxicity could be successfully predicted considering ASV-labile Cu concentrations in the samples. Pb complexation by DOM was only detected in the DOM-enriched samples and caused little effect on Pb EC50. This effect was contrary for both elutriates: one elutriate reduced Pb toxicity in comparison with the control artificial seawater, while the other increased it. UV irradiation of the samples caused a marked increase in Pb toxicity, which correlated with the remaining DOC concentration. DOM parameters were related to Cu speciation and toxicity: good correlations were found between DOC and Cu EC50, while LCu correlated better with the fluorescence of marine humic substances. The present results stress the importance of characterizing not only the amount but also the quality of seawater DOM to better predict ecological effects from total metal concentration dataP.S-M was granted with an FPU-fellowship from the Spanish Ministry of 15 Education and Science. J.S-E thanks the Basque Government for financial support (pre-doctoral grant). Research was partially funded by the project PGIDIT-05MA40201PR (Xunta de Galicia) and CTM2006-13880-C03-01/MAR (Spanish Ministry of Education and Science).Peer reviewe

Fresh and saline submarine groundwater discharge in a large coastal inlet affected by seasonal upwelling

Original research paperSubmarine groundwater discharge is recognized as a major source of chemicals to the global ocean, exerting large control over coastal water composition. Radon and 226Ra are used to evaluate, for the first time, the occur rence and magnitude of submarine groundwater discharge in the Ría de Vigo, a large, highly productive embay ment affected by seasonal, wind-driven upwelling. The system is naturally enriched in 222Rn due to the regional granitic basement geology: high 222Rn activities (up to 106 Bq m−3 ) are detected in wells and boreholes in the drainage basin of the embayment. High 222Rn activities (>400 Bq m−3 ) are also measured in certain areas of the embayment. Comparatively lower 226Ra activities (<4 103 Bq m−3 ) were measured in the freshwater sources to the bay. Mass balances obtained with a box model are used to perform a volumetric estimate of fresh and saline submarine groundwater discharge in the Ría de Vigo under contrasting circulation patterns. Fresh groundwater is shown to be a relevant hydrological component of the Ria de Vigo water balance, equivalent to 9% 4% and 23% 9% of the volume discharged by tributary rivers during winter and summer, respectively. On the other hand, recirculation of seawater through permeable sediments is capable of filtering the entire upper volume of the Ria de Vigo through its seafloor in <100 days and might thus be a previously overlooked major source of regenerated solutes to the system.Irish Research Council and European Union Commission Horizon 2020 research and innovation programmeVersión del editor3,38