Coastal North Sea Waters Research Articles

Photo‐Reactivity of Surfactants in the Sea‐Surface Microlayer and Subsurface Water of the Tyne Estuary, UK

AbstractWe report the first estimates of total surfactant photo‐reactivity in the sea‐surface microlayer (SML) and in subsurface water (SSW) (Tyne estuary, UK; salinity 0.3–32.0). In addition to temperature, a known driver of surfactant adsorption kinetics, we show that irradiation contributes independently to enhanced interfacial surfactant activity (SA), a notion supported by coincident CDOM photodegradation. We estimate a mean SA production via irradiation of 0.064 ± 0.062 mg l−1 T‐X‐100 equivalents h−1 in the SML and 0.031 ± 0.025 mg l−1 T‐X‐100 equivalents h−1 in the SSW. Using these data, we derive first‐order estimates of the potential suppression of the gas transfer velocity (kw) by photo‐derived surfactants ∼12.9%–22.2% in coastal North Sea water. Given the ubiquitous distribution of natural surfactants in the oceans, we contend that surfactant photochemistry could be a hitherto unrecognized additional driver of air‐sea gas exchange, with potential implications for global trace gas budgets and climate models.

Direct measurement of ATP in seawater and application of ATP to monitor bacterial growth potential in SWRO pre-treatment systems

The use of adenosine triphosphate (ATP) to monitor bacterial growth potential of seawater is currently not possible as ATP cannot be accurately measured at low concentration in seawater using commercially available luciferase-based ATP detection. The limitation is due to interference of salt with the luciferin–luciferase reaction, which inhibits light production. This research demonstrates that new reagents developed for (i) ATP extraction from microbial cells and (ii) ATP detection in seawater are able to reliably detect Microbial ATP as low as 0.3 ng L–1 in seawater. The luminescence signal of the new detection reagent is significantly higher (>20 times) than the luminescence signal of the freshwater reagent, when applied in seawater. ATP can now be used to monitor bacterial growth potential (BGP) through pre-treatment trains of seawater reverse osmosis (SWRO) plants. The level of detection of the new BGP test is significantly lower than the estimated threshold value required to prevent biofouling in SWRO systems. The new reagents have been used to monitor Microbial ATP in coastal North Sea water. Moreover, Microbial ATP has been applied to monitor the bacterial growth potential (using indigenous bacteria) through the pre-treatment train of an SWRO desalination plant. A significant reduction (>55%) of the bacterial growth potential was found through the dual media filtration with 4.5 mg-Fe(III) L–1 coagulant. Overall, the new reagents can detect low Microbial ATP concentrations in seawater and can be used to monitor bacterial growth potential in seawater desalination plants.

Responses of the coastal bacterial community to viral infection of the algae Phaeocystis globosa

The release of organic material upon algal cell lyses has a key role in structuring bacterial communities and affects the cycling of biolimiting elements in the marine environment. Here we show that already before cell lysis the leakage or excretion of organic matter by infected yet intact algal cells shaped North Sea bacterial community composition and enhanced bacterial substrate assimilation. Infected algal cultures of Phaeocystis globosa grown in coastal North Sea water contained gamma- and alphaproteobacterial phylotypes that were distinct from those in the non-infected control cultures 5 h after infection. The gammaproteobacterial population at this time mainly consisted of Alteromonas sp. cells that were attached to the infected but still intact host cells. Nano-scale secondary-ion mass spectrometry (nanoSIMS) showed ∼20% transfer of organic matter derived from the infected (13)C- and (15)N-labelled P. globosa cells to Alteromonas sp. cells. Subsequent, viral lysis of P. globosa resulted in the formation of aggregates that were densely colonised by bacteria. Aggregate dissolution was observed after 2 days, which we attribute to bacteriophage-induced lysis of the attached bacteria. Isotope mass spectrometry analysis showed that 40% of the particulate (13)C-organic carbon from the infected P. globosa culture was remineralized to dissolved inorganic carbon after 7 days. These findings reveal a novel role of viruses in the leakage or excretion of algal biomass upon infection, which provides an additional ecological niche for specific bacterial populations and potentially redirects carbon availability.

A novel marine nitrite-oxidizing Nitrospira species from Dutch coastal North Sea water

Marine microorganisms are important for the global nitrogen cycle, but marine nitrifiers, especially aerobic nitrite oxidizers, remain largely unexplored. To increase the number of cultured representatives of marine nitrite-oxidizing bacteria (NOB), a bioreactor cultivation approach was adopted to first enrich nitrifiers and ultimately nitrite oxidizers from Dutch coastal North Sea water. With solely ammonia as the substrate an active nitrifying community consisting of novel marine Nitrosomonas aerobic ammonia oxidizers (ammonia-oxidizing bacteria) and Nitrospina and Nitrospira NOB was obtained which converted a maximum of 2 mmol of ammonia per liter per day. Switching the feed of the culture to nitrite as a sole substrate resulted in a Nitrospira NOB dominated community (approximately 80% of the total microbial community based on fluorescence in situ hybridization and metagenomic data) converting a maximum of 3 mmol of nitrite per liter per day. Phylogenetic analyses based on the 16S rRNA gene indicated that the Nitrospira enriched from the North Sea is a novel Nitrospira species with Nitrospira marina as the next taxonomically described relative (94% 16S rRNA sequence identity). Transmission electron microscopy analysis revealed a cell plan typical for Nitrospira species. The cytoplasm contained electron light particles that might represent glycogen storage. A large periplasmic space was present which was filled with electron dense particles. Nitrospira-targeted polymerase chain reaction analyses demonstrated the presence of the enriched Nitrospira species in a time series of North Sea genomic DNA samples. The availability of this new Nitrospira species enrichment culture facilitates further in-depth studies such as determination of physiological constraints, and comparison to other NOB species.

Photochemical production and consumption of ammonium in a temperate river–sea system

We carried out 12 irradiation experiments under artificial light using samples collected from two UK upland temperate rivers, the Tyne and the Tay, and from the Tyne estuary and adjacent coastal North Sea waters. During these experiments, we followed concentration changes of ammonium (NH 4 +) and spectral changes of chromophoric dissolved organic matter (CDOM). In all experiments CDOM absorbance followed pseudo-first-order loss kinetics and photochemical NH 4 + production occurred consistently. However, the patterns of NH 4 + concentration changes with time were complex. Experiments in which irradiated waters were sampled at approximately 10 min intervals revealed an initial lag phase of ∼ 30 to 120 min during which NH 4 + concentrations did not change significantly. This lag phase was followed by a net photoproduction phase, and finally an apparent NH 4 + consumption phase. Such behaviour has not previously been reported and appeared to be independent of sample origin, initial NH 4 + concentration and initial CDOM absorption coefficient at 350 nm ( a 350). The observed behaviour could be described by a 3-stage irreversible reaction model: A → B → NH 4 + → D with first-order rate constants ka, kb and kc for the 3 consecutive reaction steps. Both ka and kc were significantly correlated ( p < 0.05) to the logarithm of the product of a 350 and salinity over the CDOM spectral slope ( S 290–350) through multiple linear regression analysis, suggesting that dissolved organic matter (DOM) properties associated with CDOM absorbance characteristics play an important role in this photochemical process. NH 4 + photoproduction rates, calculated over the lag- and production-phases, were significantly correlated with the initial a 350 for the River Tyne (including tributaries) samples, but not when samples from the estuary, coastal North Sea and River Tay were included. We also tested for possible correlations between CDOM photobleaching and spectral properties, but found no significant correlations between NH 4 + photoproduction rates and the initial spectral slope of CDOM or the CDOM photooxidation rate constants at 285, 310, 350 and 390 nm.

Characterization of azaspiracids in plankton size-fractions and isolation of an azaspiracid-producing dinoflagellate from the North Sea

Azaspiracids (AZAs) are a group of lipophilic polyether toxins implicated in incidents of shellfish poisoning in humans, particularly in northern Europe. In an attempt to establish the biogeographical distribution of AZA toxins, their association with plankton size-fractions, and to confirm the identity of the causative species responsible for human poisoning, a month-long oceanographic study was undertaken in coastal North Sea waters. The occurrence and abundance of AZA analogues was measured by on board triple quadrupole mass spectrometry coupled to liquid chromatography (LC-MS/MS). In size-fractionated plankton samples collected by net tows (20 μm mesh-size), by pumping from discrete depths and from Niskin entrapment bottle casts to fixed depths, AZA-1 was consistently the major azaspiracid component. In eastern Scottish coastal waters, the highest amounts of AZA-1 in net tow samples were in the 50–200 μm fractions, with lesser amounts detected in the >200 μm and 50–20 μm fractions. At these stations, the 50–200 μm fractions were rich in the ciliate Favella ehrenbergii. Cells of F. ehrenbergii isolated by microcapillary indeed contained AZA-1, but isolated cells grown and fed the non-toxic dinoflagellate Scrippsiella trochoidea for one week failed to contain any detectable AZA-1—evidence that F. ehrenbergii is merely a vector for AZA. Detailed analysis of plankton from Niskin bottle samples from around the North Sea typically showed highest amounts of AZA in the 3–20 μm fraction. From this fraction, a large number of crude cultures were established and subsequently screened for the presence of AZAs. A small photosynthetic thecate dinoflagellate, provisionally designated as strain 3D9, was isolated by microcapillary and brought into pure culture. This dinoflagellate strain was found to produce AZA-1, AZA-2 and an isomer of AZA-2. Sequence comparisons by molecular genetic techniques also indicated that this genotype was present in field samples rich in AZA. This discovery of a novel causative dinoflagellate for AZA toxicity essentially explains the lack of correlation of AZA with the abundance and distribution of the previously postulated culprit species Protoperidinium crassipes. We instead propose that such large phagotrophic dinoflagellates can act as an AZA vector following grazing upon a proximal source, such as the dinoflagellate 3D9 strain.

A long‐term chlorophyll dataset reveals regime shift in North Sea phytoplankton biomass unconnected to nutrient levels

During the 1980s, a rapid increase in the Phytoplankton Colour Index (PCI), a semiquantitative visual estimate of algal biomass, was observed in the North Sea as part of a regionwide regime shift. Two new data sets created from the relationship between the PCI and SeaWiFS chlorophyll a (Chl a) quantify differences in the previous and current regimes for both the anthropogenically affected coastal North Sea and the comparatively unaffected open North Sea. The new regime maintains a 13% higher Chl a concentration in the open North Sea and a 21% higher concentration in coastal North Sea waters. However, the current regime has lower total nitrogen and total phosphorus concentrations than the previous regime, although the molar N: P ratio in coastal waters is now well above the Redfield ratio and continually increasing. Besides becoming warmer, North Sea waters are also becoming clearer (i.e., less turbid), thereby allowing the normally light‐limited coastal phytoplankton to more effectively utilize lower concentrations of nutrients. Linear regression analyses indicate that winter Secchi depth and sea surface temperature are the most important predictors of coastal Chl a, while Atlantic inflow is the best predictor of open Chl a; nutrient concentrations are not a significant predictor in either model. Thus, despite decreasing nutrient concentrations, Chl a continues to increase, suggesting that climatic variability and water transparency may be more important than nutrient concentrations to phytoplankton production at the scale of this study.

Roseobacter and SAR11 dominate microbial glucose uptake in coastal North Sea waters

Bacterial assemblages in coastal pelagic environments are exposed to pronounced temporal and spatial fluctuations in the availability of monomeric substrates. Little is known about the response of particular bacterial groups to such variability. We studied glucose incorporation at various concentrations (0.1-100 nM) by bacteria related to Roseobacter, SAR11, Gammaproteobacteria and Cytophaga-Flavobacteria in coastal North Sea waters in late winter and during a spring phytoplankton bloom dominated by Phaeocystis sp. (March and May 2004 respectively). Both the fraction of glucose-assimilating bacterial cells and the rate of substrate incorporation per active cell were higher in May. The respective contributions of the studied groups to all glucose-assimilating Bacteria were related to substrate concentration. The majority of glucose-incorporating bacterial cells at the lower concentrations were members of the Roseobacter and SAR11 clades. At both time-points the two groups formed approximately equal fractions of all glucose-incorporating bacteria. This was due to a small population of highly active Roseobacter cells and high abundances of SAR11 bacteria with low proportions of glucose-incorporating cells. By contrast, the proportion of active cells from the Cytophaga-Flavobacteria lineage substantially increased at higher levels of available substrate. The determination of concentration-dependent substrate incorporation patterns may help to better understand the different ecophysiological niches of bacterioplankton populations.

Estimating the Impact of High-Production-Volume Chemicals on Remote Ecosystems by Toxic Pressure Calculation

Although many chemicals are in use, the environmental impacts of only a few have been established, usually on per-chemical basis. Uncertainty remains about the overall impact of chemicals. This paper estimates combined toxic pressure on coastal North Sea ecosystems from 343 high-production-volume chemicals used within the catchment of rivers Rhine, Meuse, and Scheldt. Multimedia fate modeling and species sensitivity distribution-based effects estimation are applied. Calculations start from production volumes and emission rates and use physicochemical substance properties and aquatic ecotoxicity data. Parameter uncertainty is addressed by Monte Carlo simulations. Results suggest that the procedure is technically feasible. Combined toxic pressure of all 343 chemicals in coastal North Seawater is 0.025 (2.5% of the species are exposed to concentration levels above EC50 values), with a wide confidence interval of nearly 0-1. This uncertainty appears to be largely due to uncertainties in interspecies variances of aquatic toxicities and, to a lesser extent, to uncertainties in emissions and degradation rates. Due to these uncertainties, the results support gross ranking of chemicals in categories: negligible and possibly relevant contributions only. With 95% confidence, 283 of the 343 chemicals (83%) contribute negligibly (less than 0.1%) to overall toxic pressure, and only 60 (17%) need further consideration.

Diurnal Variation of Cell Proliferation in Three Bacterial Taxa from Coastal North Sea Waters

Pulse-labeling with bromodeoxyuridine (BrdU) in combination with fluorescence in situ hybridization was applied to quantify the percentage of proliferating cells in coastal North Sea waters. In order to assess diurnal variability, we sampled eight or nine times, respectively, within 3 consecutive days at two seasons. Bacteria affiliated with the Roseobacter, SAR86, and NOR5 lineages constituted on average 19% +/- 3%, 8% +/- 2%, and 6% +/- 1% of all cells in May 2002 and 17% +/- 3%, 10% +/- 2%, and 11% +/- 3% in August. The relative abundances of the three populations either remained stable, or they changed very gradually during the observation periods. On average, 38 and 39% of all Bacteria exhibited DNA de novo synthesis in May and August, respectively. The fractions of proliferating cells in bacteria of the SAR86 (May, 59%; August, 72%) and the Roseobacter (48 and 53%) lineages were significantly above the community average. A substantial cell proliferation of population NOR5 (34%) was only encountered in August, concomitant with a dinoflagellate bloom. Significant short-term fluctuations of DNA-synthesizing cells were observed in Roseobacter during May and in NOR5 during August, hinting at a pronounced (temporal or spatial) mesoscale patchiness of growth rates in these populations. Since the BrdU proliferation assay is susceptible to misinterpretation, we also modeled the expected number of labeled cells at increasing BrdU incubation times in a slowly growing bacterial population. We suggest that the absence of visible DNA synthesis in marine bacterioplankton cells after DNA pulse-labeling must not be interpreted as an indication of cell "inactivity."

Are readily culturable bacteria in coastal North Sea waters suppressed by selective grazing mortality?

We studied the growth of six culturable bacterial lineages from coastal North Sea picoplankton in environmental samples under different incubation conditions. The grazing pressure of heterotrophic nanoflagellates (HNF) was reduced either by double prefiltration through 0.8- micro m-pore-size filters or by 10-fold dilutions with 0.2- micro m (pore-size) prefiltered seawater. We hypothesized that those gamma-proteobacterial genera that are rapidly enriched would also be most strongly affected by HNF regrowth. In the absence of HNF, the mean protein content per bacterial cell increased in both treatments compared to environmental samples, whereas the opposite trend was found in incubations of unaltered seawater. Significant responses to the experimental manipulations were observed in Alteromonas, Pseudoalteromonas, and Vibrio populations. No treatment-specific effects could be detected for members of the Roseobacter group, the Cytophaga latercula-C. marinoflava lineage, or the NOR5 clade. Statistical analysis confirmed a transient increase in the proportions of Alteromonas, Pseudoalteromonas, and Vibrio cells at reduced HNF densities only, followed by an overproportional decline during the phase of HNF regrowth. Cells from these genera were significantly larger than the community average in the dilution treatments, and changes in their relative abundances were negatively correlated with HNF densities. Our findings suggest that bacteria affiliated with frequently isolated genera such as Alteromonas, Pseudoalteromonas, and Vibrio might be rare in coastal North Sea picoplankton because their rapid growth response to changing environmental conditions is counterbalanced by a higher grazing mortality.

Identification of DNA-synthesizing bacterial cells in coastal North Sea plankton.

We describe a method for microscopic identification of DNA-synthesizing cells in bacterioplankton samples. After incubation with the halogenated thymidine analogue bromodeoxyuridine (BrdU), environmental bacteria were identified by fluorescence in situ hybridization (FISH) with horseradish peroxidase (HRP)-linked oligonucleotide probes. Tyramide signal amplification was used to preserve the FISH staining during the subsequent immunocytochemical detection of BrdU incorporation. DNA-synthesizing cells were visualized by means of an HRP-labeled antibody Fab fragment and a second tyramide signal amplification step. We applied our protocol to samples of prefiltered (pore size, 1.2 micro m) North Sea surface water collected during early autumn. After 4 h of incubation, BrdU incorporation was detected in 3% of all bacterial cells. Within 20 h the detectable DNA-synthesizing fraction increased to >14%. During this period, the cell numbers of members of the Roseobacter lineage remained constant, but the fraction of BrdU-incorporating Roseobacter sp. cells doubled, from 24 to 42%. In Alteromonas sp. high BrdU labeling rates after 4 to 8 h were followed by a 10-fold increase in abundance. Rapid BrdU incorporation was also observed in members of the SAR86 lineage. After 4 h of incubation, cells affiliated with this clade constituted 8% of the total bacteria but almost 50% of the visibly DNA-synthesizing bacterial fraction. Thus, this clade might be an important contributor to total bacterioplankton activity in coastal North Sea water during periods of low phytoplankton primary production. The small size and low ribosome content of SAR86 cells are probably not indications of inactivity or dormancy.

Exotic flagellates of coastal North Sea waters

Flagellate species have been shown to survive transocean passage by ballast water and the large dinoflagellateGymnodinium catenatum was introduced from Japanese to Tasmanian waters in this way.Gymnodinium mikimotoi—better known asGyrodinium aureolum—andFibrocapsa japonica as well asAlexandrium leeii are good candidates to have been introduced recently. Species which seem to have been introduced recently into the North Sea but apparently are transported from adjacent seas by currents into the region areGymnodinium chlorophorum andAlexandrium minutum. Species reported as introduced due to misidentifications areGymnodinium catenatum andLepidodinium viride. Under other names the speciesProrocentrum minimum, Prorocentrum redfieldii, andHeterosigma akashiwo have been known for a long time in the North Sea. The recent reports of threeChattonella species may be either due to introduction or they have been overlooked. The reasons why the introduction of flagellates into coastal North Sea waters is difficult to prove will be discussed.

Particulate dimethyl sulphoxide in seawater:production by microplankton

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 167:291-296 (1998) - doi:10.3354/meps167291 Particulate dimethyl sulphoxide in seawater: production by microplankton Rafel Simó*, Angela D. Hatton**, Gillian Malin, Peter S. Liss School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom *Present address: Institut de Ciències del Mar (CSIC), Pg Don Joan de Borbó s/n, E-08039 Barcelona, Catalonia, Spain. E-mail: rsimo@icm.csic.es **Present address: Dunstaffnage Marine Laboratory, Oban, Argyll PA34 4AD, United Kingdom Dimethyl sulphoxide (DMSO) represents a major pool of dissolved dimethylated sulphur in seawater. However, the origin and fate of this compound in the marine environment, and its role in the biogeochemical cycle of dimethyl sulphide (DMS), remain unclear. The only established route for the formation of DMSO in oxygenated seawater is photochemical oxidation of DMS. It is not known whether significant biotic production pathways exist. In a study of methylated sulphur speciation in coastal North Sea waters and cultures of marine unicellular algae, we measured pools of particulate DMSO (DMSO p) at nanomolar and micromolar concentrations, respectively. Analyses of size-fractionated seawater particulates and incubation experiments provided evidence that DMSO p was associated with microplanktonic organisms. Log-phase cultures of Amphidinium carterae and Emilianiahuxleyi exhibited intracellular dimethylsulphoniopropionate (DMSP) to DMSO molar ratios of 25 and 8, respectively. Our results strongly suggest the existence of biological production and release of DMSO in eukaryotic microplankton. Dimethyl sulphoxide · Phytoplankton · Dimethylsulphoniopropionate · Dimethyl sulphide · Amphidinium carterae Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 167. Publication date: June 18, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Some kinetic characteristics of exoproteolytic activity in coastal seawater

The response of the exoproteolytic activity of seawater to proteolytic inhibitors suggests that metalloproteases are the main enzymes involved. The K m of exoproteolytic enzymes for the hydrolysis of indigenous proteins in coastal north seawater has been evaluated as 80 μg l −1 and the maximum rate of proteolysis lies in the range 0·1–0·35 μgC l −1-enzymatic-unit −1. Enrichment experiments suggest that both species selection and metabolic regulation may play a role in the exoproteolytic activity/biomass ratio. However, in situ exoproteolytic activity/biomass ratios observed in a broad range of natural marine environments lie in a very narrow range, which is intermediate between those observed after amino acid or protein enrichment.