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Christiane Lancelot - One of the best experts on this subject based on the ideXlab platform.

  • Ecologically based indicators for Phaeocystis disturbance in eutrophied Belgian coastal waters (Southern North Sea) based on field observations and ecological modelling
    Journal of Sea Research, 2009
    Co-Authors: Christiane Lancelot, Véronique Rousseau, Nathalie Gypens
    Abstract:

    Recent field observations of Phaeocystis globosa colonies (number, size and cell content) and historical ecosystem model simulations have been used to define and diagnose undesirable eutrophication in the Belgian coastal zone (BCZ) as recommended by the EU Water Framework Directive and OSPAR. The proposed methodology included an initial definition of a reference abundance of Phaeocystis cells from which the disturbance could be scaled. This number was based on the Phaeocystis attribute that creates ecosystem disturbance: the ability of Phaeocystis colonies to grow and reach sizes unmanageable for the current copepods. The threshold was set at 4 × 106 cells L− 1 and corresponded to the maximum Phaeocystis cells contained in the grazable colonies (< 400 µm) recorded in the BCZ between 1988 and 2000. Interestingly, this cell number was similar to the maximum number of Phaeocystis colony cells simulated for pristine time by the coupled RIVERSTRAHLER-MIRO (R-MIRO) model, suggesting that natural Phaeocystis ecosystems are well balanced and efficiently transfer their production to higher trophic levels. However, both the field observations obtained during the 1988–2000 period and the 1950–2000 historical reconstruction of eutrophication in the BCZ simulated by the R-MIRO model showed Phaeocystis colony cell maxima well above the threshold value. Considering that a return to the pristine reference value is not achievable, another methodology was then proposed based on historical R-MIRO simulations of annual primary (PP) and copepod (CP) productions where the CP:PP ratio can be considered an indicator of trophic efficiency. The analysis of changing CP:PP ratios in relationship with simulated winter concentrations and annual inputs of nutrients showed that the decrease in trophic efficiency was related to the imbalanced DIN and DIP inputs (N:P > 25) explained here by the reduction in DIP loads after 1985 while DIN remained elevated. On this basis, a critical DIN load estimated at 60 kT y− 1 was proposed to re-equilibrate the N:P balance in the BCZ and to favour diatoms over Phaeocystis colonies. More generally we conclude that N:P ratios in nutrient loads (or winter stocks in the coastal area) in excess of 25 in Phaeocystis ecosystems are indicative of Phaeocystis colony dominance and weak trophic efficiency.info:eu-repo/semantics/publishe

  • modelling the relative impact of rivers scheldt rhine seine and western channel waters on the nutrient and diatoms Phaeocystis distributions in belgian waters southern north sea
    Continental Shelf Research, 2007
    Co-Authors: Genevieve Lacroix, Nathalie Gypens, Kevin Ruddick, Christiane Lancelot
    Abstract:

    The coastal areas of the Southern North Sea (SNS) experience eutrophication problems resulting from freshwater nitrogen (N) and phosphorus (P) inputs from rivers. In particular, massive blooms of Phaeocystis colonies occur in Belgian waters. In this region, water masses result from the mixing of Western Channel (WCH) waters transported through the Straits of Dover with nutrient-rich freshwater from the Scheldt, the Rhine and Meuse, the Seine, the Thames and other smaller rivers. However, the relative contribution of the WCH and each river to the inorganic nutrient pool and the impact on the phytoplankton community structure (diatoms and Phaeocystis) are not known. In order to effectively manage the eutrophication problems, it is necessary to know: (i) the relative contribution of the WCH and of each river impacting the region and (ii) the relative effect of a N and/or P nutrient reduction on the Phaeocystis blooms. To answer these questions, sensitivity tests (1% nutrient reduction) and nutrient reduction scenarios (50% nutrient reduction) have been performed with a three-dimensional (3D) coupled physical-biogeochemical model (MIRO&CO-3D). MIRO&CO-3D results from the coupling of the COHERENS 3D hydrodynamic model with the ecological model MIRO. The model has been set up for the region between 48.5 degrees N, 4 degrees W and 52.5 degrees N, 4.5 degrees E and run to simulate the annual cycle of carbon, inorganic and organic nutrients, phytoplankton (diatoms and Phaeocystis), bacteria and zooplankton (microzooplankfon and copepods) in the SNS under realistic forcing (meteorology and river inputs) for the period 1991-2003. The relative contribution of the WCH waters and of the different rivers on the inorganic nutrient pool available for phytoplankton (diatoms and Phaeocystis) growth is assessed by decreasing by 1% the nutrient (dissolved inorganic nitrogen, DIN and inorganic phosphate, PO4) inputs from the WCH and from, respectively, the Scheldt (and smaller Belgian rivers), the Rhine/Meuse and the Seine (and smaller French rivers) [sensitivity tests]. The relative role of N and P reduction on the diatomsIPhaeocystis distribution is further explored by simulations with 50% reduction of the total (inorganic and organic) N and total P river inputs [nutrient reduction scenarios]. These scenarios allow assessing the impact of the expected 50% reduction of river nutrient inputs resulting from the implementation of nutrient reduction policy. Results of the sensitivity tests suggest that the impact of a 1% reduction of river nutrient inputs on surface nutrients (DIN and PO4) over the Belgian Exclusive Economic Zone (EEZ) area is similar for the Seine and the Scheldt, which are in turn greater than for the Rhine. However, a hypothetical 1% reduction of nutrient input from the WCH boundary would have a higher impact than for the Scheldt. The impact of nutrient reduction is higher for DIN than for PO4 whatever the river (contrary to the WCH). DIN is more sensitive to riverine nutrient reduction because the rivers are over enriched in DIN compared to PO4. The sensitivity tests suggest also that a PO4 river input reduction would result in a NY increase and a DIN river input reduction would result in a NY decrease but that a combined (PO4 and DIN) input reduction would reduce the NT ratio at sea. From 50% nutrient reduction scenarios, model results suggest that a total P reduction would induce a significant decrease of diatoms and a small (coast) to negligible (offshore) decrease of Phaeocystis biomass. On the contrary, a total N reduction would induce a significant decrease of Phaeocystis biomass and a moderate increase of diatoms. When N and P river input reductions are combined, the model predicts a significant decrease of Phaeocystis biomass in Belgian waters and a significant decrease of diatom biomass in the coastal waters and a small increase offshore. A future management plan aiming at Phaeocystis reduction should thus prioritise N reduction. (c) 2007 Elsevier Ltd. All rights reserved.

  • Current understanding of Phaeocystis ecology and biogeochemistry, and perspectives for future research
    Phaeocystis major link in the biogeochemical cycling of climate-relevant elements, 2007
    Co-Authors: Peter G. Verity, Christiane Lancelot, Jens C. Nejstgaard, Corina P. Brussaard, Maria A. Van Leeuwe, Linda K. Medlin
    Abstract:

    The phytoplankton genus Phaeocystis has well-documented, spatially and temporally extensive blooms of gelatinous colonies; these are associated with release of copious amounts of dimethyl sulphide (an important climate-cooling aerosol) and alterations of material flows among trophic levels and export from the upper ocean. A potentially salient property of the importance of Phaeocystis in the marine ecosystem is its physiological capability to transform between solitary cell and gelatinous colonial life cycle stages, a process that changes organism biovolume by 6-9 orders of magnitude, and which appears to be activated or stimulated under certain circumstances by chemical communication. Both life-cycle stages can exhibit rapid, phased ultradian growth. The colony skin apparently confers protection against, or at least reduces losses to, smaller zooplankton grazers and perhaps viruses. There are indications that Phaeocystis utilizes chemistry and/or changes in size as defenses against predation, and its ability to create refuges from biological attack is known to stabilize predator-prey dynamics in model systems. Thus the life cycle form in which it occurs, and particularly associated interactions with viruses, determines whether Phaeocystis production flows through the traditional great fisheries food chain, the more regenerative microbial food web, or is exported from the mixed layer of the ocean. Despite this plethora of information regarding the physiological ecology of Phaeocystis, fundamental interactions between life history traits and system ecology are poorly understood. Research summarized here, and described in the various papers in this special issue, derives from a central question: how do physical (light, temperature, particle distributions, hydrodynamics), chemical (nutrient resources, infochemistry, allelopathy), biological (grazers, viruses, bacteria, other phytoplankton), and self-organizational mechanisms (stability, indirect effects) interact with life-cycle transformations of Phaeocystis to mediate ecosystem patterns of trophic structure, biodiversity, and biogeochemical fluxes? Ultimately the goal is to understand and thus predict why Phaeocystis occurs when and where it does, and the bio-feedbacks between this keystone species and the multitrophic level ecosystem. © 2007 Springer Science+Business Media B.V.SCOPUS: ch.binfo:eu-repo/semantics/publishe

  • Current understanding of Phaeocystis ecology and biogeochemistry, and perspectives for future research
    Biogeochemistry, 2007
    Co-Authors: Peter G. Verity, Christiane Lancelot, Jens C. Nejstgaard, Corina P. Brussaard, Maria A. Van Leeuwe, Linda K. Medlin
    Abstract:

    The phytoplankton genus Phaeocystis has well-documented, spatially and temporally extensive blooms of gelatinous colonies; these are associated with release of copious amounts of dimethyl sulphide (an important climate-cooling aerosol) and alterations of material flows among trophic levels and export from the upper ocean. A potentially salient property of the importance of Phaeocystis in the marine ecosystem is its physiological capability to transform between solitary cell and gelatinous colonial life cycle stages, a process that changes organism biovolume by 6–9 orders of magnitude, and which appears to be activated or stimulated under certain circumstances by chemical communication. Both life-cycle stages can exhibit rapid, phased ultradian growth. The colony skin apparently confers protection against, or at least reduces losses to, smaller zooplankton grazers and perhaps viruses. There are indications that Phaeocystis utilizes chemistry and/or changes in size as defenses against predation, and its ability to create refuges from biological attack is known to stabilize predator–prey dynamics in model systems. Thus the life cycle form in which it occurs, and particularly associated interactions with viruses, determines whether Phaeocystis production flows through the traditional “great fisheries” food chain, the more regenerative microbial food web, or is exported from the mixed layer of the ocean. Despite this plethora of information regarding the physiological ecology of Phaeocystis, fundamental interactions between life history traits and system ecology are poorly understood. Research summarized here, and described in the various papers in this special issue, derives from a central question: how do physical (light, temperature, particle distributions, hydrodynamics), chemical (nutrient resources, infochemistry, allelopathy), biological (grazers, viruses, bacteria, other phytoplankton), and self-organizational mechanisms (stability, indirect effects) interact with life-cycle transformations of Phaeocystis to mediate ecosystem patterns of trophic structure, biodiversity, and biogeochemical fluxes? Ultimately the goal is to understand and thus predict why Phaeocystis occurs when and where it does, and the bio-feedbacks between this keystone species and the multitrophic level ecosystem.info:eu-repo/semantics/publishe

  • Current understanding of Phaeocystis ecology and biogeochemistry, and perspectives for future research
    Biogeochemistry, 2007
    Co-Authors: Peter P. Verity, Christiane Lancelot, Jens C. Nejstgaard, Corina P. D. Brussaard, Maria A. Van Leeuwe, Linda K. Medlin
    Abstract:

    The phytoplankton genus Phaeocystis has well-documented, spatially and temporally extensive blooms of gelatinous colonies; these are associated with release of copious amounts of dimethyl sulphide (an important climate-cooling aerosol) and alterations of material flows among trophic levels and export from the upper ocean. A potentially salient property of the importance of Phaeocystis in the marine ecosystem is its physiological capability to transform between solitary cell and gelatinous colonial life cycle stages, a process that changes organism biovolume by 6–9 orders of magnitude, and which appears to be activated or stimulated under certain circumstances by chemical communication. Both life-cycle stages can exhibit rapid, phased ultradian growth. The colony skin apparently confers protection against, or at least reduces losses to, smaller zooplankton grazers and perhaps viruses. There are indications that Phaeocystis utilizes chemistry and/or changes in size as defenses against predation, and its ability to create refuges from biological attack is known to stabilize predator–prey dynamics in model systems. Thus the life cycle form in which it occurs, and particularly associated interactions with viruses, determines whether Phaeocystis production flows through the traditional “great fisheries” food chain, the more regenerative microbial food web, or is exported from the mixed layer of the ocean.

Véronique Rousseau - One of the best experts on this subject based on the ideXlab platform.

  • Ecologically based indicators for Phaeocystis disturbance in eutrophied Belgian coastal waters (Southern North Sea) based on field observations and ecological modelling
    Journal of Sea Research, 2009
    Co-Authors: Christiane Lancelot, Véronique Rousseau, Nathalie Gypens
    Abstract:

    Recent field observations of Phaeocystis globosa colonies (number, size and cell content) and historical ecosystem model simulations have been used to define and diagnose undesirable eutrophication in the Belgian coastal zone (BCZ) as recommended by the EU Water Framework Directive and OSPAR. The proposed methodology included an initial definition of a reference abundance of Phaeocystis cells from which the disturbance could be scaled. This number was based on the Phaeocystis attribute that creates ecosystem disturbance: the ability of Phaeocystis colonies to grow and reach sizes unmanageable for the current copepods. The threshold was set at 4 × 106 cells L− 1 and corresponded to the maximum Phaeocystis cells contained in the grazable colonies (< 400 µm) recorded in the BCZ between 1988 and 2000. Interestingly, this cell number was similar to the maximum number of Phaeocystis colony cells simulated for pristine time by the coupled RIVERSTRAHLER-MIRO (R-MIRO) model, suggesting that natural Phaeocystis ecosystems are well balanced and efficiently transfer their production to higher trophic levels. However, both the field observations obtained during the 1988–2000 period and the 1950–2000 historical reconstruction of eutrophication in the BCZ simulated by the R-MIRO model showed Phaeocystis colony cell maxima well above the threshold value. Considering that a return to the pristine reference value is not achievable, another methodology was then proposed based on historical R-MIRO simulations of annual primary (PP) and copepod (CP) productions where the CP:PP ratio can be considered an indicator of trophic efficiency. The analysis of changing CP:PP ratios in relationship with simulated winter concentrations and annual inputs of nutrients showed that the decrease in trophic efficiency was related to the imbalanced DIN and DIP inputs (N:P > 25) explained here by the reduction in DIP loads after 1985 while DIN remained elevated. On this basis, a critical DIN load estimated at 60 kT y− 1 was proposed to re-equilibrate the N:P balance in the BCZ and to favour diatoms over Phaeocystis colonies. More generally we conclude that N:P ratios in nutrient loads (or winter stocks in the coastal area) in excess of 25 in Phaeocystis ecosystems are indicative of Phaeocystis colony dominance and weak trophic efficiency.info:eu-repo/semantics/publishe

  • Hydroclimatic modulation of diatom/Phaeocystis blooms in nutrient‐enriched Belgian coastal waters (North Sea)
    Limnology and Oceanography, 2006
    Co-Authors: Elsa Breton, Véronique Rousseau, Jean-yves Parent, J. Ozer, Christiane Lancelot
    Abstract:

    Statistical analysis of 14 yr (1988–2001) of intensive phytoplankton monitoring at Station 330 in the central Belgian Coastal Zone (BCZ, Southern Bight of the North Sea) indicates that the long-term diatom biomass trend and the spring dominance of Phaeocystis colonies over diatoms are determined by the combined effect of the North Atlantic Oscillation (NAO) and freshwater and continental nitrate carried by the Scheldt. The strong correlation between diatoms and the NAO index is largely explained by the modulating effect of the latter on the water budget at the monitoring station. The relationship between Phaeocystis spring blooms and winter NAO (NAOw) is indirect, better expressed by springtime Phaeocystis dominance over diatoms because of the higher response of the latter to the NAO. The spring Phaeocystis : diatom bloom ratio is negatively (or positively) linked to positive (or negative) NAOw values. A complex cascade of events links large-scale NAO index variations with those local meteorological conditions (wind strength and direction, rainfall) that drive the hydrography and water budget of the BCZ. Local meteorological conditions in turn modulate the geographical spread of Scheldt nutrient loads in the coastal zone and ultimately regulate the magnitude of Phaeocystis spring blooms by determining winter nitrate enrichment. Hence, the absence of a linear relationship between Phaeocystis spring blooms and NAOw is explained by the nonlinear response of river-based nitrate pulses to NAO due to local wind-driven hydrodynamical forcing.

  • hydroclimatic modulation of diatom Phaeocystis blooms in nutrient enriched belgian coastal waters north sea
    Limnology and Oceanography, 2006
    Co-Authors: Elsa Breton, Véronique Rousseau, Jean-yves Parent, J. Ozer, Christiane Lancelot
    Abstract:

    Statistical analysis of 14 yr (1988–2001) of intensive phytoplankton monitoring at Station 330 in the central Belgian Coastal Zone (BCZ, Southern Bight of the North Sea) indicates that the long-term diatom biomass trend and the spring dominance of Phaeocystis colonies over diatoms are determined by the combined effect of the North Atlantic Oscillation (NAO) and freshwater and continental nitrate carried by the Scheldt. The strong correlation between diatoms and the NAO index is largely explained by the modulating effect of the latter on the water budget at the monitoring station. The relationship between Phaeocystis spring blooms and winter NAO (NAOw) is indirect, better expressed by springtime Phaeocystis dominance over diatoms because of the higher response of the latter to the NAO. The spring Phaeocystis : diatom bloom ratio is negatively (or positively) linked to positive (or negative) NAOw values. A complex cascade of events links large-scale NAO index variations with those local meteorological conditions (wind strength and direction, rainfall) that drive the hydrography and water budget of the BCZ. Local meteorological conditions in turn modulate the geographical spread of Scheldt nutrient loads in the coastal zone and ultimately regulate the magnitude of Phaeocystis spring blooms by determining winter nitrate enrichment. Hence, the absence of a linear relationship between Phaeocystis spring blooms and NAOw is explained by the nonlinear response of river-based nitrate pulses to NAO due to local wind-driven hydrodynamical forcing.

  • The fate of Phaeocystis-derived fatty acids and associated material during a Phaeocystis globosa bloom in the Southern North Sea
    2003
    Co-Authors: Christian Hamm, Véronique Rousseau
    Abstract:

    Abstract: The fate of a Phaeocystis globosa bloom in the Southern North Sea off Belgium, the Netherlands and Germany in Mai 1995 was investigated during a cruise with RV Belgica. We used fatty acids as biomarkers to follow the fate of Phaeocystis-derived biomass of a Phaeocystis dominated spring bloom. The Phaeocystis bloom showed a fatty acid composition with a characteristic dominance of polyunsaturated C18-fatty acids, which increased in concentration with number of double bonds up to 18:5 (n-3), and high concentrations of 20:5 (n-3) and 22:6 (n-3). In contrast to most previous studies, fatty acid analysis of the mesozooplankton community (mainly calanoid copepods) and meroplankton (Carcinus maenas megalope) demonstrated that Phaeocystis was a major component in the diet of these organisms. Massive accumulations of amorphous grey aggregates, in which Phaeocystis colonies were major components, were dominated by saturated fatty acids and only few of the polyunsaturated C18-fatty acids. A hydrophobic surface slick that covered the water surface during the bloom showed very similar patterns. Foam patches contained few Phaeocystis-typical fatty acids, but increased amounts of diatom-typical compounds such as 16:1 (n-7) and 20:5 (n-3), and 38% fatty alcohols, indicating that wax esters dominated the lipid fraction in the foam with ca. 76% (w/w). The fatty acid compositions of surface sediment showed that no sedimentation of fresh Phaeocystis occurred during the study. The results indicate that diverse processes degrade Phaeocystis -derived organic matter while floating or in suspension, and little evidence for a massive sedimentation of the Phaeocystis bloom.

  • Composition, assimilation and degradation of Phaeocystis globosa-derived fatty acids in the North Sea
    Journal of Sea Research, 2003
    Co-Authors: Christian Hamm, Véronique Rousseau
    Abstract:

    The fate of a Phaeocystis globosa bloom in the southern North Sea off Belgium, the Netherlands and Germany in May 1995 was investigated during a cruise with RV ‘Belgica’. We used fatty acids as biomarkers to follow the fate of Phaeocystis-derived biomass of a Phaeocystis-dominated spring bloom. The bloom, in which up to >99% of the biomass was contributed by Phaeocystis, showed a fatty acid composition with a characteristically high abundance of polyunsaturated C18-fatty acids, which increased in concentration with number of double bonds up to 18:5 (n-3), and high concentrations of 20:5 (n-3) and 22:6 (n-3). In contrast to most previous studies, fatty acid analysis of the mesozooplankton community (mainly calanoid copepods) and meroplankton (Carcinus maenas megalope) indicated that P. globosa was a major component (ca. 70% and 50%, respectively) in the diet of these organisms. Massive accumulations of amorphous grey aggregates, in which Phaeocystis colonies were major components, were dominated by saturated fatty acids and contained only few of the polyunsaturated C18-fatty acids. A hydrophobic surface slick that covered the water surface during the bloom showed very similar patterns. Foam patches contained few Phaeocystis-typical fatty acids, but increased amounts of diatom-typical compounds such as 16:1 (n-7) and 20:5 (n-3), and 38% fatty alcohols, indicating that wax esters dominated the lipid fraction in the foam with ca. 76% (w/w). The fatty acid compositions of surface sediment showed that no sedimentation of fresh Phaeocystis occurred during the study. The results indicate that Phaeocystis-derived organic matter degraded while floating or in suspension, and had not reached the sediment in substantial amounts.

Winfried W.c. Gieskes - One of the best experts on this subject based on the ideXlab platform.

  • Phaeocystis, major link in the biogeochemical cycling of climate-relevant elements - Phaeocystis, major link in the biogeochemical cycling of climate-relevant elements
    2007
    Co-Authors: Van Maria Leeuwe, Jacqueline Stefels, Christiane Lancelot, Sauveur Belviso, Peter G. Verity, Winfried W.c. Gieskes
    Abstract:

    A taxonomic review of the genus Phaeocystis.- Methods used to reveal genetic diversity in the colony-forming prymnesiophytes Phaeocystis antarctica, P. globosa and P. pouchetii-preliminary results.- The life cycle of Phaeocystis: state of knowledge and presumptive role in ecology.- Phaeocystis colony distribution in the North Atlantic Ocean since 1948, and interpretation of long-term changes in the Phaeocystis hotspot in the North Sea.- Photosynthetic responses in Phaeocystis antarctica towards varying light and iron conditions.- Effects of iron concentration on pigment composition in Phaeocystis antarctica grown at low irradiance.- Evidence for high iron requirements of colonial Phaeocystis antarctica at low irradiance.- The carbohydrates of Phaeocystis and their degradation in the microbial food web.- The role of iron in the bacterial degradation of organic matter derived from Phaeocystis antarctica.- The colonization of two Phaeocystis species (Prymnesiophyceae) by pennate diatoms and other protists: a significant contribution to colony biomass.- Zooplankton grazing on Phaeocystis: a quantitative review and future challenges.- The influence of Phaeocystis globosa on microscale spatial patterns of chlorophyll a and bulk-phase seawater viscosity.- Haemolytic activity of live Phaeocystis pouchetii during mesocosm blooms.- Phaeocystis and its interaction with viruses.- Does Phaeocystis spp. contribute significantly to vertical export of organic carbon?.- Vernal sedimentation trends in north Norwegian fjords: temporary anomaly in 234Th particulate fluxes related to Phaeocystis pouchetii proliferation.- Environmental constraints on the production and removal of the climatically active gas dimethylsulphide (DMS) and implications for ecosystem modelling.- Variability in abundance and fluxes of dimethyl sulphide in the Indian Ocean.- Gaining integrated understanding of Phaeocystis spp. (Prymnesiophyceae) through model-driven laboratory and mesocosm studies.- Current understanding of Phaeocystis ecology and biogeochemistry, and perspectives for future research.

  • Acrylate in Phaeocystis colonies does not affect the surrounding bacteria
    Journal of Sea Research, 2000
    Co-Authors: D.j B Noordkamp, Winfried W.c. Gieskes, Jan C. Gottschal, L.j Forney, Van Marion Rijssel
    Abstract:

    Acrylate accumulates to concentrations of 1.3-6.5 mM in the mucus of Phaeocystis colonies and may have an effect on the surrounding bacterial community, either as an inhibitor or as a carbon source. Both in the held and in the laboratory, effects of acrylate on bacterial growth and on its consumption were investigated. During a Phaeocystis bloom, acrylate-consuming bacteria were found to be present (1% of total number counted by microscopy) and a 5-fold increase of the number of these bacteria was observed after the Phaeocystis bloom (4.9% of the total number counted by microscopy). Acrylate consumption rates were higher in filtered (less than or equal to 20 mu m) seawater samples than in unfiltered samples, indicating that particles larger than 20 mu m, mostly Phaeocystis colonies, caused a reduction in the rate of acrylate consumption. This was not found when axenic Phaeocystis was added to an acrylate-consuming bacterium (strain AC-2) that had been isolated from the highest MPN dilution from field samples. Furthermore, we could not find a decrease in growth rates of the total bacterial community or of isolated strains in the presence of high acrylate concentrations (less than or equal to 10 mM). In co-cultures of Phaeocystis and strain AC-2 we observed that the production of acrylate was not affected by the bacterium and that the consumption of acrylate by strain AC-2 was not affected by the presence of Phaeocystis. Acrylate concentrations in the mucous layer of the Phaeocystis colonies in those cocultures were high (6.7-7.7 mM) and comparable with acrylate concentrations in the mucous layer of axenic Phaeocystis colonies. Acrylate seems to be sorbed to the mucus matrix of the colony and diffusion of acrylate out of this mucus matrix appears to be slow. Upon disruption of the colony skin acrylate was immediately solubilised from the mucus matrix. (C) 2000 Elsevier Science B.V. All rights reserved.

  • An inventory of factors that affect polysaccharide production by Phaeocystis globosa
    Journal of Sea Research, 2000
    Co-Authors: Van Marion Rijssel, D.j B Noordkamp, I Janse, Winfried W.c. Gieskes
    Abstract:

    Abstract Phaeocystis material contains polysaccharides that are built from at least eight different monosaccharides. Differences have been reported between the carbohydrate composition of different Phaeocystis species, and also between samples taken from Phaeocystis globosa blooms in different areas. In order to elucidate factors that could play a role in determining variation in carbohydrate composition and production, a number of Phaeocystis globosa strains were studied under laboratory conditions. Although there was a clear distinction of a northern and a southern cluster in the Phaeocystis globosa strains based on RAPD analysis, the differences in the composition of the mucopolysaccharides were relatively small. The contribution of glucose, however, ranged from 7–85% of total sugars. A strain that was cultured in seawaters of diverse origin produced polysaccharides of a different composition, suggesting the effect of environmental factors. The presence of bacteria affected neither the amount, nor the composition of the carbohydrates that were produced by Phaeocystis globosa . Glucose is part of both the intracellular polysaccharide pool and of the mucopolysaccharides in the colony matrix. Using specific digestion of the intracellular chrysolaminaran by laminarinase, the distribution of polysaccharides over different pools could be assessed. During growth of an axenic, mucus-producing strain, the portion of glucose present as chrysolaminaran appeared to increase. The polyglucose that was not digested by laminarinase remains unidentified. This study shows that environmental factors rather than strain differences determine differences in the sugar composition of Phaeocystis globosa , especially with respect to the glucose content of the material. A difference in the contribution of glucose could be correlated to the portion of cells in the culture that are not in the colonies. Our study emphasises that for studying polysaccharide dynamics in Phaeocystis globosa it is important to be able to discriminate between the different polysaccharide pools. Preliminary results of an enzymatic approach were promising

  • development of the diatom Phaeocystis spring bloom in the dutch coastal zone of the north sea the silicon depletion versus the daily irradiance threshold hypothesis
    Journal of Plankton Research, 1998
    Co-Authors: L Peperzak, Winfried W.c. Gieskes, F Colijn, J. C. H. Peeters
    Abstract:

    The Dutch coastal zone of the North Sea is characterized by high nutrient inputs and low water column irradiance due to high concentrations of suspended matter. The vernal phytoplankton blooms are dominated by diatoms and the flagellate Phaeocystis (Haptophyta). Two hypotheses that predict the timing of the Phaeocystis bloom were tested with field data collected in 1992. The first one, stating that the Phaeocystis bloom starts when silicon has been depleted by a preceding diatom bloom, could not be bracketed with observations. The second hypothesis, predicting that Phaeocystis blooms under nitrogen- and phosphorus-replete conditions after a daily irradiance threshold has been passed could be supported by field observations. Furthermore, it is shown that the Dutch coastal zone is not continuously homogeneously mixed. It is argued that this is an important factor in the life cycle of Phaeocystis and in foam formation on nearby shores. Grazing by the ciliate Strombidium sulcatum and heterotrophic gymnodinoid flagellates accounted for 92% of Phaeocystis cell loss after the bloom.

  • Carbohydrates in the North Sea during spring blooms of Phaeocystis : A specific fingerprint
    Aquatic Microbial Ecology, 1996
    Co-Authors: Ingmar Janse, Christiane Lancelot, Jan C. Gottschal, Marion Van Rijssel, Winfried W.c. Gieskes
    Abstract:

    Regional and temporal variation in the composition of water-soluble carbohydrates from Phaeocystis colonies sampled in the southern North Sea was small during spring 1994, except for a high variability in the contribution of glucose. Glucose is universally present in storage products of microalgae; the relative constancy of the carbohydrate pattern of the other monosaccharides suggests that these are part of the more refractory colony mucus. In all Phaeocystis samples arabinose dominated, followed by xylose (Belgian coast) or galactose and mannose (Dutch coast). Rhamnose, glucuronate and O-methylated sugars were present in lower amounts. The latter, always present in samples containing Phaeocystis, may be typical for North Sea strains. The sugar patterns we report here differ from those presented in the literature concerning Phaeocystis-derived material, and also from the sugar fingerprint in the preceding diatom bloom. The Phaeocystis mucus apparently behaves as particulate matter since it was retained on filters of over 1 mu m. This characteristic together with its refractory nature, typical of 'transparent exopolymer particles' (TEPs), must have consequences for the heterotrophic microbial community in terms of adherence and substrate availability.

Jacqueline Stefels - One of the best experts on this subject based on the ideXlab platform.

  • Global marine plankton functional type biomass distributions: Phaeocystis spp.
    Earth System Science Data, 2012
    Co-Authors: M. Vogt, J. Peloquin, V. Schoemann, Elsa Breton, M. Estrada, D. Karentz, M. A. Van Leeuwe, Colleen J. O'brien, John A. E. Gibson, Jacqueline Stefels
    Abstract:

    Abstract. The planktonic haptophyte Phaeocystis has been suggested to play a fundamental role in the global biogeochemical cycling of carbon and sulphur, but little is known about its global biomass distribution. We have collected global microscopy data of the genus Phaeocystis and converted abundance data to carbon biomass using species-specific carbon conversion factors. Microscopic counts of single-celled and colonial Phaeocystis were obtained both through the mining of online databases and by accepting direct submissions (both published and unpublished) from Phaeocystis specialists. We recorded abundance data from a total of 1595 depth-resolved stations sampled between 1955–2009. The quality-controlled dataset includes 5057 counts of individual Phaeocystis cells resolved to species level and information regarding life-stages from 3526 samples. 83% of stations were located in the Northern Hemisphere while 17% were located in the Southern Hemisphere. Most data were located in the latitude range of 50–70° N. While the seasonal distribution of Northern Hemisphere data was well-balanced, Southern Hemisphere data was biased towards summer months. Mean species- and form-specific cell diameters were determined from previously published studies. Cell diameters were used to calculate the cellular biovolume of Phaeocystis cells, assuming spherical geometry. Cell biomass was calculated using a carbon conversion factor for prymnesiophytes. For colonies, the number of cells per colony was derived from the colony volume. Cell numbers were then converted to carbon concentrations. An estimation of colonial mucus carbon was included a posteriori, assuming a mean colony size for each species. Carbon content per cell ranged from 9 pg C cell−1 (single-celled Phaeocystis antarctica) to 29 pg C cell−1 (colonial Phaeocystis globosa). Non-zero Phaeocystis cell biomasses (without mucus carbon) range from 2.9 × 10−5 to 5.4 × 103 μg C l−1, with a mean of 45.7 μg C l−1 and a median of 3.0 μg C l−1. The highest biomasses occur in the Southern Ocean below 70° S (up to 783.9 μg C l−1) and in the North Atlantic around 50° N (up to 5.4 × 103 μg C l−1). The original and gridded data can be downloaded from PANGAEA, doi:10.1594/PANGAEA.779101 .

  • Phaeocystis, major link in the biogeochemical cycling of climate-relevant elements - Phaeocystis, major link in the biogeochemical cycling of climate-relevant elements
    2007
    Co-Authors: Van Maria Leeuwe, Jacqueline Stefels, Christiane Lancelot, Sauveur Belviso, Peter G. Verity, Winfried W.c. Gieskes
    Abstract:

    A taxonomic review of the genus Phaeocystis.- Methods used to reveal genetic diversity in the colony-forming prymnesiophytes Phaeocystis antarctica, P. globosa and P. pouchetii-preliminary results.- The life cycle of Phaeocystis: state of knowledge and presumptive role in ecology.- Phaeocystis colony distribution in the North Atlantic Ocean since 1948, and interpretation of long-term changes in the Phaeocystis hotspot in the North Sea.- Photosynthetic responses in Phaeocystis antarctica towards varying light and iron conditions.- Effects of iron concentration on pigment composition in Phaeocystis antarctica grown at low irradiance.- Evidence for high iron requirements of colonial Phaeocystis antarctica at low irradiance.- The carbohydrates of Phaeocystis and their degradation in the microbial food web.- The role of iron in the bacterial degradation of organic matter derived from Phaeocystis antarctica.- The colonization of two Phaeocystis species (Prymnesiophyceae) by pennate diatoms and other protists: a significant contribution to colony biomass.- Zooplankton grazing on Phaeocystis: a quantitative review and future challenges.- The influence of Phaeocystis globosa on microscale spatial patterns of chlorophyll a and bulk-phase seawater viscosity.- Haemolytic activity of live Phaeocystis pouchetii during mesocosm blooms.- Phaeocystis and its interaction with viruses.- Does Phaeocystis spp. contribute significantly to vertical export of organic carbon?.- Vernal sedimentation trends in north Norwegian fjords: temporary anomaly in 234Th particulate fluxes related to Phaeocystis pouchetii proliferation.- Environmental constraints on the production and removal of the climatically active gas dimethylsulphide (DMS) and implications for ecosystem modelling.- Variability in abundance and fluxes of dimethyl sulphide in the Indian Ocean.- Gaining integrated understanding of Phaeocystis spp. (Prymnesiophyceae) through model-driven laboratory and mesocosm studies.- Current understanding of Phaeocystis ecology and biogeochemistry, and perspectives for future research.

  • Adaptation to fluctuating light and iron limitation by Phaeocystis antarctica
    Science Access, 2001
    Co-Authors: Jacqueline Stefels, M. A. Van Leeuwe
    Abstract:

    The marine phytoplankton genus Phaeocystis has a world-wide distribution and is able to form almost uni-algal blooms in coastal areas and in polar regions. Notwithstanding its successfulness in plankton communities, only little is know about its physiological ability to adapt to multiple stress regimes as prevailing in the Southern Ocean: fluctuating light as a result of strong vertical mixing and iron limitation. Under such conditions, cells are jeopardised by photoinhibition. Previous experiments under iron-limitation have shown that, besides a shift in the ratio of diatoxanthin to diadinoxanthin, Phaeocystis exhibits shifts in the pool of butanoyloxyfucoxanthin, hexanoyloxyfucoxanthin and fucoxanthin. It was hypothesised that a possible fucoxanthin cycle is an additional means of dissipating excess light energy under iron limitation. Here we present data on photoacclimation, as measured by fluorescence parameters, in vivo absorption and pigmentation, in lab experiments with Phaeocystis antarctica. Experiments were performed with iron-deplete and iron-replete cultures under conditions of fluctuating light, mimicking vertical mixing.

  • DMSP synthesis and exudation in phytoplankton: a modeling approach
    Marine Ecology Progress Series, 1999
    Co-Authors: D Laroche, Alain F. Vézina, Maurice Levasseur, Michel Gosselin, Jacqueline Stefels, Maureen D. Keller, Patricia A. Matrai, Rlj Kwint
    Abstract:

    In the marine environment, phytoplankton are the fundamental producers of dimethylsulfoniopropionate (DMSP), the precursor of the climatically active gas dimethylsulfide (DMS). DMSP is released by exudation, cell autolysis, and zooplankton grazing during phytoplankton blooms. In this study, we developed a model of phytoplankton DMSP and DMS production allowing quantification of the exudation rates of these compounds during different growth phases. The model was tested on published data from axenic cultures of Prorocentrum minimum and Phaeocystis sp.; DMSP exudation rates vary considerably between the 2 species. Model results show that P. minimum exudes around 1% d(-1) of its DMSP quota during the latent, exponential and senescent phases. This is comparable to the average exudation rate estimated from previous laboratory experiments. However, Phaeocystis sp. exudes from 3 to 11% d(-1) of its DMSP quota. For this species, DMSP exudation rates apparently show an inverse relationship with the population growth rate. The maximum DMSP exudation rate in Phaeocystis sp. is 10 times higher than previously reported DMSP or DMS exudation rates. Our results suggest that exudation may be as important as cell autolysis in the release of DMSP during Phaeocystis sp. blooms. We conclude that exudation should be incorporated in models of DMS cycling in the marine environment. Moreover, our results for Phaeocystis sp. suggest that a low and constant exudation rate, as sometimes used in models, is not suitable for all conditions.

  • Intriguing Functionality of the Production and Conversion of DMSP in Phaeocystis SP
    Biological and Environmental Chemistry of DMSP and Related Sulfonium Compounds, 1996
    Co-Authors: Jacqueline Stefels, Winfried W.c. Gieskes, Lubbert Dijkhuizen
    Abstract:

    In many areas of the ocean the distribution and conversion of dimethylsulfoniopropionate (DMSP) may to a high degree be influenced by the activity of the Prymnesiophyte alga Phaeocystis sp.: it not only produces DMSP in large amounts, but is also able to convert it enzymatically into dimethylsulfide (DMS) and acrylate. Characteristic properties of DMSP-lyase in Phaeocystis sp. indicate that the enzyme is different from lyase enzymes in other organisms studied. During a spring bloom in Dutch coastal waters, DMSP-lyase activity was strongly correlated with Phaeocystis sp. cell numbers and potentially capable of producing DMS in excess of abiotic loss factors. In Phaeocystis sp. cells, DMSP makes an important contribution to the intracellular osmotic potential, with concentrations of approximately 150 mM. Upon salinity shocks, however, short term regulation of its internal levels was not observed. Although a slow adaptation of the DMSP production in Phaeocystis sp. cells may affect intracellular concentrations on a long term, it is concluded that DMSP-lyase is not involved in the short term osmotic adaptation of the cell. DMSP is a structural component of the cell, being produced continuously in the light as well as in the dark. DMSP-lyase activity facilitates the release of DMSP from the cell, with some intriguing beneficial effects.

Peter G. Verity - One of the best experts on this subject based on the ideXlab platform.

  • Current understanding of Phaeocystis ecology and biogeochemistry, and perspectives for future research
    Phaeocystis major link in the biogeochemical cycling of climate-relevant elements, 2007
    Co-Authors: Peter G. Verity, Christiane Lancelot, Jens C. Nejstgaard, Corina P. Brussaard, Maria A. Van Leeuwe, Linda K. Medlin
    Abstract:

    The phytoplankton genus Phaeocystis has well-documented, spatially and temporally extensive blooms of gelatinous colonies; these are associated with release of copious amounts of dimethyl sulphide (an important climate-cooling aerosol) and alterations of material flows among trophic levels and export from the upper ocean. A potentially salient property of the importance of Phaeocystis in the marine ecosystem is its physiological capability to transform between solitary cell and gelatinous colonial life cycle stages, a process that changes organism biovolume by 6-9 orders of magnitude, and which appears to be activated or stimulated under certain circumstances by chemical communication. Both life-cycle stages can exhibit rapid, phased ultradian growth. The colony skin apparently confers protection against, or at least reduces losses to, smaller zooplankton grazers and perhaps viruses. There are indications that Phaeocystis utilizes chemistry and/or changes in size as defenses against predation, and its ability to create refuges from biological attack is known to stabilize predator-prey dynamics in model systems. Thus the life cycle form in which it occurs, and particularly associated interactions with viruses, determines whether Phaeocystis production flows through the traditional great fisheries food chain, the more regenerative microbial food web, or is exported from the mixed layer of the ocean. Despite this plethora of information regarding the physiological ecology of Phaeocystis, fundamental interactions between life history traits and system ecology are poorly understood. Research summarized here, and described in the various papers in this special issue, derives from a central question: how do physical (light, temperature, particle distributions, hydrodynamics), chemical (nutrient resources, infochemistry, allelopathy), biological (grazers, viruses, bacteria, other phytoplankton), and self-organizational mechanisms (stability, indirect effects) interact with life-cycle transformations of Phaeocystis to mediate ecosystem patterns of trophic structure, biodiversity, and biogeochemical fluxes? Ultimately the goal is to understand and thus predict why Phaeocystis occurs when and where it does, and the bio-feedbacks between this keystone species and the multitrophic level ecosystem. © 2007 Springer Science+Business Media B.V.SCOPUS: ch.binfo:eu-repo/semantics/publishe

  • Current understanding of Phaeocystis ecology and biogeochemistry, and perspectives for future research
    Biogeochemistry, 2007
    Co-Authors: Peter G. Verity, Christiane Lancelot, Jens C. Nejstgaard, Corina P. Brussaard, Maria A. Van Leeuwe, Linda K. Medlin
    Abstract:

    The phytoplankton genus Phaeocystis has well-documented, spatially and temporally extensive blooms of gelatinous colonies; these are associated with release of copious amounts of dimethyl sulphide (an important climate-cooling aerosol) and alterations of material flows among trophic levels and export from the upper ocean. A potentially salient property of the importance of Phaeocystis in the marine ecosystem is its physiological capability to transform between solitary cell and gelatinous colonial life cycle stages, a process that changes organism biovolume by 6–9 orders of magnitude, and which appears to be activated or stimulated under certain circumstances by chemical communication. Both life-cycle stages can exhibit rapid, phased ultradian growth. The colony skin apparently confers protection against, or at least reduces losses to, smaller zooplankton grazers and perhaps viruses. There are indications that Phaeocystis utilizes chemistry and/or changes in size as defenses against predation, and its ability to create refuges from biological attack is known to stabilize predator–prey dynamics in model systems. Thus the life cycle form in which it occurs, and particularly associated interactions with viruses, determines whether Phaeocystis production flows through the traditional “great fisheries” food chain, the more regenerative microbial food web, or is exported from the mixed layer of the ocean. Despite this plethora of information regarding the physiological ecology of Phaeocystis, fundamental interactions between life history traits and system ecology are poorly understood. Research summarized here, and described in the various papers in this special issue, derives from a central question: how do physical (light, temperature, particle distributions, hydrodynamics), chemical (nutrient resources, infochemistry, allelopathy), biological (grazers, viruses, bacteria, other phytoplankton), and self-organizational mechanisms (stability, indirect effects) interact with life-cycle transformations of Phaeocystis to mediate ecosystem patterns of trophic structure, biodiversity, and biogeochemical fluxes? Ultimately the goal is to understand and thus predict why Phaeocystis occurs when and where it does, and the bio-feedbacks between this keystone species and the multitrophic level ecosystem.info:eu-repo/semantics/publishe

  • Haemolytic activity of live Phaeocystis pouchetii during mesocosm blooms
    Biogeochemistry, 2007
    Co-Authors: Marion Van Rijssel, Jens C. Nejstgaard, Andrey F. Sazhin, Anne-carlijn Alderkamp, Peter G. Verity
    Abstract:

    Chemical defence is a potential mechanism contributing to the success of Phaeocystis species that repeatedly dominate the phytoplankton in coastal areas. Species within the genus Phaeocystis have long been suspected of imposing negative effects on co-occurring organisms. Recently a number of toxins have been extracted and identified from Phaeocystis samples, but it is not clear if they do enhance the competitive advantage of Phaeocystis species. In the present study the cytotoxic impact of live Phaeocystis pouchetii to human blood cells in close proximity, regardless of the nature of the responsible mechanism, was quantified using a bioassay. Haemolytic activity was measured during blooms of P. pouchetii in mesocosms. These environments were chosen to mimic natural conditions including chemically mediated interactions that could trigger defensive and/or allelopathic responses of Phaeocystis. Haemolytic activity correlated with P. pouchetii numbers and was absent during the preceding diatom bloom. Samples containing live P. pouchetii cells showed the highest activity, while filtered sea water and cell extracts were less haemolytic or without effect. Dose-response curves were linear up to 70% lysis, and haemolysis in samples containing live P. pouchetii cells reached EC50 values comparable to known toxic prymnesiophytes (1.9 * 10(7) cells l(-1)). Haemolytic activity was enhanced by increased temperature and light. The results indicate that unprotected and thus presumably vulnerable cells present in a P. pouchetii bloom may lyse within days

  • gaining integrated understanding of Phaeocystis spp prymnesiophyceae through model driven laboratory and mesocosm studies
    Biogeochemistry, 2007
    Co-Authors: Peter G. Verity, Jens C. Nejstgaard, Marc E. Frischer, Jeremy D. Long, Stuart J Whipple, Bernard C Patten, Jon T Anderson, Anita Jacobsen, Aud Larsen
    Abstract:

    Knowledge of the complex life cycle of Phaeocystis is a key to understanding its role in marine ecosystems and global biogeochemistry. An existing life cycle model was modified and used to integrate understanding of the Phaeocystis life cycle. In model-driven research, models expose gaps in our understanding, empirical studies ensue, and feedback improves understanding. Following this scheme, three facets of the life cycle model were examined here. With four exceptions, the empirical studies described have been presented in other literature citations. The first facet involved testing for the existence of a process or producing its description. These studies included: demonstration of in vitro colony division in Phaeocystis pouchetii, description of in vitro change in colony shape for P. pouchetii associated with senescence, determining which P. pouchetii life stage is vulnerable to viral infection and lysis, and an experiment designed to determine whether the sediment could be a source of new Phaeocystis colonies to overlying waters; results suggested that more-detailed investigation of benthic particles as a physical substrate for colony formation is warranted. The second facet involved investigation of process rate quantification or process control parameters. Process rate quantification included measurements of colony division rate and growth rate using mesocosm-derived colonies. Process control experiments included testing diatom frustule enhancement of P. pouchetii colony formation from solitary cells, and investigation of mesozooplanktonic suppression and microzooplanktonic enhancement of Phaeocystis globosa colony formation by planktonic grazer infochemicals. The third facet pertained to the molecular identification of genetic differences between single cells and colonies of P. globosa. These studies were designed to provide insight to the question of control factors involved in the transition between single cell and colonial life stages. The life cycle model provided a ready place to incorporate new insights and understanding from empirical studies into an existing model, and can be used to improve simulation models of the direct and indirect effects of Phaeocystis on global biogeochemistry.

  • Phaeocystis, major link in the biogeochemical cycling of climate-relevant elements - Phaeocystis, major link in the biogeochemical cycling of climate-relevant elements
    2007
    Co-Authors: Van Maria Leeuwe, Jacqueline Stefels, Christiane Lancelot, Sauveur Belviso, Peter G. Verity, Winfried W.c. Gieskes
    Abstract:

    A taxonomic review of the genus Phaeocystis.- Methods used to reveal genetic diversity in the colony-forming prymnesiophytes Phaeocystis antarctica, P. globosa and P. pouchetii-preliminary results.- The life cycle of Phaeocystis: state of knowledge and presumptive role in ecology.- Phaeocystis colony distribution in the North Atlantic Ocean since 1948, and interpretation of long-term changes in the Phaeocystis hotspot in the North Sea.- Photosynthetic responses in Phaeocystis antarctica towards varying light and iron conditions.- Effects of iron concentration on pigment composition in Phaeocystis antarctica grown at low irradiance.- Evidence for high iron requirements of colonial Phaeocystis antarctica at low irradiance.- The carbohydrates of Phaeocystis and their degradation in the microbial food web.- The role of iron in the bacterial degradation of organic matter derived from Phaeocystis antarctica.- The colonization of two Phaeocystis species (Prymnesiophyceae) by pennate diatoms and other protists: a significant contribution to colony biomass.- Zooplankton grazing on Phaeocystis: a quantitative review and future challenges.- The influence of Phaeocystis globosa on microscale spatial patterns of chlorophyll a and bulk-phase seawater viscosity.- Haemolytic activity of live Phaeocystis pouchetii during mesocosm blooms.- Phaeocystis and its interaction with viruses.- Does Phaeocystis spp. contribute significantly to vertical export of organic carbon?.- Vernal sedimentation trends in north Norwegian fjords: temporary anomaly in 234Th particulate fluxes related to Phaeocystis pouchetii proliferation.- Environmental constraints on the production and removal of the climatically active gas dimethylsulphide (DMS) and implications for ecosystem modelling.- Variability in abundance and fluxes of dimethyl sulphide in the Indian Ocean.- Gaining integrated understanding of Phaeocystis spp. (Prymnesiophyceae) through model-driven laboratory and mesocosm studies.- Current understanding of Phaeocystis ecology and biogeochemistry, and perspectives for future research.