Phaeocystis Colonies Research Articles

Trophic efficiency of the planktonic food web in a coastal ecosystem dominated by Phaeocystis colonies

The trophic efficiency of the planktonic food web in the Phaeocystis-dominated ecosystem of the Belgian coastal waters was inferred from the analysis of the carbon flow network of the planktonic system subdivided into its different trophodynamic groups. A carbon budget was constructed on the basis of process-level field experiments conducted during the spring bloom period of 1998. Biomass and major metabolic activities of auto- and heterotrophic planktonic communities (primary production, bacterial production, nanoproto-, micro- and mesozooplankton feeding activities) were determined in nine field assemblages collected during spring at reference station 330. In 1998, the phytoplankton spring flowering was characterised by a moderate diatom bloom followed by a massive Phaeocystis colony bloom. Phaeocystis colonies, contributing 70% to the net primary production, escaped the linear food chain while the early spring diatom production supplied 74% of the mesozooplankton carbon uptake. The rest of mesozooplankton food requirement was, at the time of the Phaeocystis colony bloom, partially fulfilled by microzooplankton. Only one-third of the microzooplankton production, however, was controlled by mesozooplankton grazing pressure. Ungrazed Phaeocystis colonies were stimulating the establishment of a very active microbial network. On the one hand, the release of free-living cells from ungrazed colonies has been shown to stimulate the growth of microzooplankton, which was controlling 97% of the nanophytoplankton production. On the other hand, the disruption of ungrazed Phaeocystis colonies supplied the water column with large amounts of dissolved organic matter available for planktonic bacteria. The budget calculation suggests that ungrazed colonies contributed up to 60% to the bacterial carbon demand, while alternative sources (exudation, zooplankton egestion and lysis of other organisms) provided some 30% of bacterial carbon requirements. This suggests that the spring carbon demand of planktonic bacteria was satisfied largely by autogenic production. The trophic efficiency was defined as the ratio between mesozooplankton grazing on a given source and food production. In spite of its major contribution to mesozooplankton feeding, the trophic efficiency of the linear food chain, restricted to the grazing on diatoms, represented only 5.6% of the available net primary production. The trophic efficiency of the microbial food chain, the ratio between mesozooplankton grazing on microzooplankton and the resource inflow (the bacterial carbon demand plus the nanophytoplankton production) amounted to only 1.6%. These low trophic efficiencies together with the potential contribution of ungrazed Phaeocystis-derived production to the bacterial carbon demand suggest that during spring 1998 most of the Phaeocystis-derived production in the Belgian coastal area was remineralised in the water column.

Acrylate in Phaeocystis colonies does not affect the surrounding bacteria

Acrylate accumulates to concentrations of 1.3–6.5mM 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 field 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 (≤20μm) seawater samples than in unfiltered samples, indicating that particles larger than 20μm, 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 (≤10mM). 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 co-cultures were high (6.7–7.7mM) 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.

Architecture, ecology and biogeochemistry of Phaeocystis colonies

This paper discusses structure and function of the Phaeocystis colony skin, and relates them to the specific impact of Phaeocystis colonies on ecology and biogeochemistry. The potential advantage of the recently discovered tough skin around the colonies of Phaeocystis globosa is discussed in context with the metabolic costs of this structure, and compared to potential functions of structures around other phytoplankton. It is further proposed that mainly small, fast-growing pathogens and predators will be deterred by the colony skin. It will be shown that these theoretical predictions are consistent with available data from the literature, and can explain the dominance of the colonial form in Phaeocystis blooms. Finally, the peculiar biogeochemistry of Phaeocystis colonies, especially the sedimentation of Phaeocystis-derived organic matter, is argued to be a function of the susceptibility of Phaeocystis colonies to certain grazers, which in turn is strongly determined by the architecture and function of the colony skin. During the exponential phase of the bloom, Phaeocystis-derived organic matter can efficiently sink in faecal material of large zooplankton, which actively feed on the colonies. However, the integrity of the colony skin, and consequently its protection for the cells therein, seems to be closely coupled to the phase of active growth. Accordingly, the cells are massively affected by small grazers and pathogens and thus rapidly disintegrate after the culmination of the bloom, so that sedimentation of Phaeocystis-derived organic matter becomes probably restricted to the more refractory extracellular components of the colonies.

Grazing experiments and model simulations of the role of zooplankton in Phaeocystis food webs

A combined empirical and modelling study was conducted to further examine the potential importance of grazing by zooplankton in pelagic food webs in which Phaeocystis is a significant or dominant component. Laboratory experiments were designed to measure ingestion of Phaeocystis and other potential prey items which co-occur with Phaeocystis. Grazers included copepods and ciliates, and prey included Phaeocystis colonies and solitary cells, diatoms, ciliates, bacteria, and detritus. These data were expressed in the model currency of nitrogen units, and fit to hyperbolic tangent equations which included minimum prey thresholds. These equations and literature data were used to constrain a food web model whose purpose was to investigate trophic interactions rather than to mimic actual events. Nevertheless, the model output was similar to the general pattern and magnitude of development of Phaeocystis–diatom communities in some environments where they occur, e.g. north Norwegian waters. The model included three forms of nitrogen, three phytoplankton groups, bacteria, two zooplankton groups, and detritus, with detailed flows between compartments. An important component of the model was inclusion of variable prey preferences for zooplankton. The experiments and model simulations suggest several salient conclusions. Phaeocystis globosa colonies were eaten by a medium-sized copepod species, but ingestion appeared to be strongly dependent upon a proper size match between grazer and prey. If not, colonies were eaten little if at all. Phaeocystis solitary cells were ingested rapidly by ciliate microzooplankton, in agreement with prior literature observations. In contrast, detritus was eaten comparatively slowly by both ciliates and copepods. Both types of zooplankton exhibited apparent minimum prey thresholds below which grazing did not occur or was inconsequential. Model simulations implied that transitions between life cycle stages of Phaeocystis may potentially be important to phytoplankton–zooplankton interactions, and that relative rates of ingestion of Phaeocystis by various zooplankton may have significant impacts upon material fluxes through and out of Phaeocystis–diatom ecosystems. Indirect effects of trophic interactions appear to be equally significant as direct effects.

Microbial food web structure in the Arabian Sea: a US JGOFS study

One of the main objectives of the Joint Global Ocean Flux Studies (JGOFS) program is to develop an understanding of the factors controlling organic carbon production in the ocean and the time-varying vertical flux of carbon from surface waters (US JGOFS (1990) US JGOFS Planning Report Number 11; Sarmiento and Armstrong (1997) US JGOFS Synthesis and Modeling Project Implementation Plan). A considerable amount of evidence suggests that carbon cycling and the potential for exporting carbon from ocean systems is a function of food web structure. As part of the US JGOFS Arabian Sea Studies, the biomass of planktonic organisms, ranging from heterotrophic bacteria through microplankton-sized organisms, was estimated using a variety of methods including flow cytometry and microscopy. This is a first attempt to combine biomass data from a number of sources, evaluate the structure of the food web, examine changes in food web structure in relation to seasonal or spatial features of the study area, and look for indications of how changing structure affects carbon-cycling processes. Biomass in the upper 100 m of the water column ranged from approximately 1.5 to >5.2 gC m −2. Heterotrophic bacteria (Hbac) made up from 16 and 44% of the biomass; autotrophs comprised 43–64%; and the remainder was made up of nano- and microheterotrophs. Autotrophs and nano- and microheterotrophs showed a general pattern of higher values at coastal stations, with the lowest values offshore. Heterotrophic bacteria (Hbac) showed no significant spatial variations. The Spring Intermonsoon and early NE Monsoon were dominated by autotrophic picoplankton, Prochlorococcus and Synechococcus. The late NE Monsoon and late SW Monsoon periods showed an increase in the larger size fractions of the primary producers. At several stations during the SW Monsoon, autotrophic microplankton, primarily diatoms and Phaeocystis colonies, predominated. Increases in the size of autotrophs were also reflected in increasing sizes of nano- and microheterorophs. The biomass estimates based on cytometry and microscopy are consistent with measurement of pigments, POC and PON. Changes in community structure were assessed using the percent similarity index (PSI) in conjunction with multidimensional scaling (MDS) or single-linkage clustering analysis to show how assemblages differed among cruises and stations. Station clustering reflected environmental heterogeneity, and many of the conspicuous changes could be associated with changes in temperature, salinity and nutrient concentrations. Despite inherent problems in combining data from a variety of sources, the present community biomass estimates were well constrained by bulk measurements such as Chl a, POC and PON, and by comparisons with other quantitative and qualitative studies. The most striking correlation between food web structure and carbon cycling was the dominance of large phytoplankton, primarily diatoms, and the seasonal maxima of mass flux during the SW Monsoon. High nutrient conditions associated with upwelling during the SW Monsoon would explain the predominance of diatoms during this season. The sinking of large, ungrazed diatom cells is one possible explanation for the flux observations, but may not be consistent with the observation of concurrent increases in larger microzooplankton consumers (heterotrophic dinoflagellates and ciliates) and mesozooplankton during this season. Food-web structure during the early NE Monsoon and Intermonsoons suggests carbon cycling by the microbial community predominated.

Diffusive boundary layers, photosynthesis, and respiration of the colony‐forming plankton algae, Phaeocystis sp

Diffusive boundary layers, photosynthesis, and respiration in Phaeocystis colonies were studied by the use of microelectrodes for oxygen and pH during a bloom in the Barents Sea, 1993, and in the Marsdiep, Dutch North Sea, 1994. The oxygen microenvironment of a Phaeocystis colony with a mean diameter of 1.4 mm was mapped from 346 O2 measurements and showed gradients of oxygen concentration in the water phase up to 1 mm distance from the colony surface. The effective diffusive boundary layer was 0.4–0.9 mm thick. Oxygen concentrations inside colonies reached 180% of the bulk water, and pH increased up to 0.4 units when measured in light at saturating intensities (>90 µmol photons m−2 s−1 ). The respiration in the dark was low, resulting in a 6% lowering in oxygen concentration and 0.04 units lowering in pH inside colonies, compared to the bulk water phase. Such colonies were net heterotrophic communities at light intensities up to 10 µmol photons m−2 s−1. A week later, colonies were net heterotrophic at light intensities up to 80 µmol photons m−2 s−1. The effective diffusion coefficient for oxygen in the gelatinous colonies was not significantly different from that in sea water.

Colonies of Phaeocystis globosa are protected by a thin but tough skin

Colonies of the prymnesiophyte marine microalga Phaeocystis globosa were tested for mechanical properties, permeability and biochemical composition using the micropipette aspiration technique. We found that the Phaeocystis colony is enclosed by a thin, yet very strong, semi-permeable skin (pore size between 1 - 4.4 nm diameter) with plastic and to a limited extent also elastic properties. Qualitative staining of single colonies with selective fluorescent dyes indicated absence of lipophilic compounds and chitin but presence of aminogroups in the colony skin. Individual cells in the colony appear to be weakly connected with one another and attached to a very dilute, peripheral gel. Suction applied to the colony resulted in volume loss due to expulsion of and squeezing together of the cells within the skin into a tight pouch; the presence of any firm gelatinous matter within the colony was not discernible. On increasing suction pressure, the skin eventually ruptured and the cells were sucked out of the hole leaving the empty skin behind. We propose that the skin effectively protects the colony cells from grazing and infection by viruses and other pathogens. The unsuspected presence of a skin is probably the main reason why Phaeocystis colonies have reduced mortality relative to solitary cells and form large blooms in many regions of the world ocean. Our findings indicate that the colonies should be viewed as bags of water rather than balls of jelly.

Effects of phytoplankton blooms on the cycling of manganese and iron in coastal waters

The development of intense plankton blooms during spring controls the concentrations of dissolved Mn and Fe in eutrophic shallow coastal waters of the North Sea. Proliferation of diatoms, Phaeocystis colonies, and Noctiluca was accompanied by changes of particulate and dissolved Mn and Fe in the water column. The latter parameters were measured simultaneously with relevant physical, chemical, and biological variables at two sites in the coastal waters of the Southem North Sea, in 1993 at one site and in 1994 at both sites. Removal of dissolved Fe and particulate Fe, Mn, and Al occurred during the inception of the spring bloom. This could be due to biological uptake, adsorption of abiotic particles onto settling phytoplankton cells, or ingestion of abiotic particles by zooplankton during grazing, with subsequent settling of fecal pellets. We also observed a seasonal increase of dissolved Mn and Fe and progressive changes in the composition of the particulate Mn and Fe in the water column after peaks in spring diatom and Phaeocystis blooms. This can be explained by the following sequence of events. The organic matter produced during the spring phytoplankton blooms is degraded by the heterotrophic organisms in the water column and the sediment. This leads to anoxic conditions near the surficial layer in the shallow coastal sediments. First, Mn oxides and then Fe oxides are used as oxidants for the degradation of organic matter, resulting in the reduction and dissolution of Mn and Fe. Dissolved Mn and Fe diffuse to the oxic overlying water and are partly adsorbed or precipitated on the suspended particulate matter. The other part remains in solution longer because of a decrease in the oxidation rate. This decrease results from a lowering of both the pH from 8.6 to 8.1 and the oxygen concentrations from 378 to 204 μM in the water column due to the activity of heterotrophs in the water column and sediment. Noctiluca could also be responsible for the reduction of Mn and Fe associated with bacteria and phytoplankton. Overall, the seasonal evolution of dissolved and particulate Mn and Fe is consistent with the successive autotrophic and heterotrophic activities.

Nano- and microplankton in the northern Arabian Sea during the Southwest Monsoon, August–September 1995 A US–JGOFS study

As part of the US Joint Global Ocean Flux Studies (JGOFS) Arabian Sea Program, we determined the abundance and biomass of autotrophic and heterotrophic nano- and microplankton in the upper 100 m at 10 stations in the northern Indian Ocean during the late Southwest Monsoon from 17 August through 15 September 1995. Autotrophic nano- and microplankton biomass ranged from 0.2 to 68.0 μg C l -1, with most of the biomass in the upper 20–60 m. Phytoplankton assemblages varied markedly in composition along a transect from onshore to about 1500 km offshore. Larger forms, such as diatoms and colonies of the prymnesiophyte Phaeocystis, dominated stations inshore of about 1000 km, whereas picoplankton dominated offshore. Heterotrophic nano- and microplankton biomass varied from ∼1 to 12 μg C l -1, and nanoflagellates, dinoflagellates, and ciliates reached maximum biomass at different locations and depths. Heterotrophs comprised 18–27% of the biomass over most of the transect. Biomass of all groups of organisms was strongly negatively correlated with depth and positively correlated with each other, suggesting a dynamic food web. Size structure of organisms among stations suggested that larger consumers occurred where phytoplankton cells were large. Sediment trap data indicate high organic carbon and biogenic silica flux at the time of our study. Our findings of abundant diatoms over much of the study area and their apparent transition from healthy-looking cells nearshore to senescent ones offshore suggest that populations could have sunk as a bloom terminated, in addition to being available for mesozooplankton grazers.

Major and comparable roles for free-living and attached bacteria in the degradation of Phaeocystis-derived organic matter in Belgian coastal waters of the North Sea

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 14:39-48 (1998) - doi:10.3354/ame014039 Major and comparable roles for free-living and attached bacteria in the degradation of Phaeocystis-derived organic matter in Belgian coastal waters of the North Sea S. Becquevort*, V. Rousseau, C. Lancelot Groupe de Microbiologie des Milieux Aquatiques, Université Libre de Bruxelles, Campus de la Plaine, CP 221, Boulevard du Triomphe, B-1050 Brussels, Belgium *E-mail: sbecq@pop.ulb.ac.be Microbial degradation of Phaeocystisglobosa colonies and their derived organic matter by free-living and attached bacteria was investigated in Belgian coastal waters during the spring development of diatom-Phaeocystis colonies in 1994. Results obtained show concomitant evolution of hydrolytic ectoprotease and b-ectoglucosidase ectoenzymatic activities with respect to the phytoplankton bloom, suggesting that the low biodegradability of Phaeocystis colonies leading to transient accumulations of Phaeocystis-derived material in the coastal North Sea was not due to a lag phase required for the induction of b-ectoglucosidase. Up to 66% of total bacterial biomass was found attached to particles larger than 10 μm. While occurring always in low abundance compared to free-living bacteria, both the average specific biomass and growth rate of particle-attached bacteria were very high, i.e. 60 fg C cell-1 and 0.28 h-1, respectively. Similarly, specific ectoenzymatic activities of particle-attached bacteria were on average about 5 times higher than those characterising free-living bacteria. Budget calculations show a 53% contribution of Phaeocystis-attached bacteria to the mineralisation of Phaeocystis-associated production, i.e. a 53:47% role for attached and free-living bacteria, respectively. Phaeocystis degradation · Free-living and particle-attached bacteria · Ectoenzymatic activity · Growth rate Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 14, No. 1. Publication date: January 02, 1998 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1998 Inter-Research.

Phaeocystis globosa (Prymnesiophyceae) colonies: hollow structures built with small amounts of polysaccharides

In both field samples and cultures the total amount of sugar and of carbon in colonies of Phaeocystis globosa was correlated with colony surface area, suggesting a hollow structure. A conceptual model based on biochemical data and on the assumption that the mucus occurs as a layer of a fixed thickness, irrespective of colony size, predicts that the thickness of the layer is 7 μm. A confocal laser scanning microscope image of fluorescently labelled mucus confirmed this view of the colony structure. The measured contents of carbon and sugar per cell (including mucus) were constant for all colony sizes. Cells in laboratory cultures contained 122 pg C, which is twice the value for cells obtained at a field station in the North Sea (57 pg). In contrast, sugar per cell was higher in the field than in exponentially growing cultures. Therefore the percentage of sugar carbon relative to total carbon of colonies in the field was higher (19–35%) than that in cultures (10%). Highest values were found at low ambient nutrient concentrations, probably due to the presence of storage glucans in the cells that are produced under nutrient limitation. The functional role of Phaeocystis colonies in the pelagic system has to be re-evaluated because (i) biomass estimates have previously often been based on the assumption of a colony filled with mucus while in reality it is a hollow structure with an aqueous lumen, and (ii) in contrast to earlier reports it is shown that only a small amount of carbohydrate is needed to build the colony structure.

Phaeocystis globosa (Prymnesiophyceae) colonies : hollow structures built with small amounts of polysaccharides

In both field samples and cultures the total amount of sugar and of carbon in colonies of Phaeocystis globosa was correlated with colony surface area, suggesting a hollow structure. A conceptual model based on biochemical data and on the assumption that the mucus occurs as a layer of a fixed thickness, irrespective of colony size, predicts that the thickness of the layer is 7 μm. A confocal laser scanning microscope image of fluorescently labelled mucus confirmed this view of the colony structure. The measured contents of carbon and sugar per cell (including mucus) were constant for all colony sizes. Cells in laboratory cultures contained 122 pg C, which is twice the value for cells obtained at a field station in the North Sea (57 pg). In contrast, sugar per cell was higher in the field than in exponentially growing cultures. Therefore the percentage of sugar carbon relative to total carbon of colonies in the field was higher (19–35%) than that in cultures (10%). Highest values were found at low ambient nutrient concentrations, probably due to the presence of storage glucans in the cells that are produced under nutrient limitation. The functional role of Phaeocystis colonies in the pelagic system has to be re-evaluated because (i) biomass estimates have previously often been based on the assumption of a colony filled with mucus while in reality it is a hollow structure with an aqueous lumen, and (ii) in contrast to earlier reports it is shown that only a small amount of carbohydrate is needed to build the colony structure.

Phosphate and plankton dynamics during a drift experiment in the German Bight:simulation of phosphorus-related plankton production

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 156:289-297 (1997) - doi:10.3354/meps156289 Phosphate and plankton dynamics during a drift experiment in the German Bight: simulation of phosphorus-related plankton production Andreas Moll* Institut für Meereskunde, Zentrum für Meeres- und Klimaforschung der Universität Hamburg, Troplowitzstr. 7, D-22529 Hamburg, Germany *E-mail: moll@ifm.uni-hamburg.de As part of the German research project PRISMA, a drift experiment conducted in the German Bight in April 1991 showed that the diatom spring bloom was ending and a Phaeocystis bloom was beginning. Due to formation of Phaeocystis colonies, zooplankton biomass declined. Phosphate, nitrate and silicate were depleted and phosphate was below limiting values. The data are interpreted using a vertically resolved phosphorus-based primary production model. The model adequately explains the phosphate development and the amplitude and timing of the algal standing stock. It is inferred that primary production in this area is high, about 1.3 g C m-2 d-1, due to excellent production conditions at the end of April. The contributions of various processes are represented by the pathways of phosphorus in the upper 30 m of the water column. Phosphate uptake amounted to 4.8 mmol m-2 for the 6 d of the experiments. Sinking of phytoplankton plus diffusion and sinking of detritus to the bottom were the sources for bottom detritus (0.6 mmol m-2). The bottom detritus was mainly supplied by phytoplankton mortality (0.3 mmol m-2) due to ciliate grazing. Inorganic phosphate was supplied via benthic remineralization and upward diffusion (0.9 mmol m-2). The overall trend of phosphate and phytoplankton indicates that nearly the same water body was sampled over the course of the drift experiment. Due to the 6-hourly observations, interruptions due to advection in most of the measured parameters are visible. For the phytoplankton concentrations, the short-term and overall differences are shown by a comparison between the central drift station and 3 additional stations placed around the central station in a triangle and located 3 nautical miles away. The drift buoy moved in and out of the bloom area. The water column model neglects horizontal advection, so it would be better employed for mesocosm experiments. In the future fully 3-dimensional models should be implemented. North Sea · German Bight · Drift experiment · Plankton dynamics · Primary production model · Phosphorus budget Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 156. Publication date: September 25, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Accumulation and sedimentation of Phaeocystis globosa in the Dutch Wadden Sea

In the Marsdiep tidal inlet, Phaeocystis globosa blooms have occurred every year since phytoplankton monitoring started in the early 1970s. A high spring peak is usually followed by lower peaks in summer. Detailed cell counts are presented for the years 1993, 1994, and 1995, of which 1994 was exceptional with a low spring peak but a much higher peak in June/July. Over tidal flats in the western Dutch Wadden Sea, I found Phaeocystis colony accumulation and cell densities one to two orders of magnitude higher than in the Marsdiep tidal inlet; colonies settled on the tidal flats, but did not become part of larger aggregates. The accumulation process resembles similar processes earlier described for fine sediments in the Wadden Sea and may be caused by similar processes. The small benthic gastropod Hydrobia ulvae at low tide grazed on colonies settled on the sediment. This loss of colonies from the water column by settling and grazing may help in rapidly decreasing P. globosa cell numbers after the spring peak in the Wadden Sea. Massive sedimentation and subsequent mineralization of Phaeocystis colonies might induce low oxygen events and mass mortality of macrobenthos, but up to now no direct relation has been reported between Phaeocystis sedimentation and mass mortality in zoobenthos.

Subsurface chlorophyll maxima in the Skagerrak-processes and plankton community structure

Subsurface chlorophyll maxima are common phenomena in both the coastal and open ocean. The main objective of this study was to clarify possible differences in the structure and function of the plankton community in subsurface chlorophyll maxima and at the surface. Sampling was performed at seven stations in the Skagerrak, northeast Atlantic, during five cruises in May and August 1992 and April, May and August 1993. Subsurface chlorophyll fluorescence maxima (FM) occurred on 25 out of 32 sampling occasions. The FMs were usually situated below the pycnocline and associated with the nutricline. The ratio of chlorophyll a to particulate carbon and the light-saturated primary production were higher for plankton at the FM than at the surface, although assimilation numbers (primary production rate: chlorophyll a) were not different from surface plankton. The light protective pigment diadinoxanthin occurred in higher concentrations relative to chlorophyll a in surface plankton than in FM plankton. Respiration was higher in the FM than at the surface. This was not related to abundance of bacteria or bacterial production since no differences between surface and FM values were detected for these parameters. FM plankton was characterized by high nutrient uptake rates, but in this study there were no significant differences compared to surface plankton. ‘New’ production was on average 25%, but up to about 50% in the western Skagerrak in spring. The average nitrogen uptake rates were dominated by the regenerated nutrients ammonium and urea, accounting for about 50 and 25%, respectively. The <3 μm size fraction contributed significantly to concentrations of total chlorophyll a, particulate carbon, and nitrogen as well as to nitrogen uptake. Its contribution was highest when total values were low. Microscopical investigations and analysis of pigments specific to algal groups showed that diatoms dominated in the FMs in spring and that peridinin-containing dinoflagellates dominated in FMs in August. Autotrophic nanoplankton was dominated by the Prymnesiophyceae contributing about 50% of total cell numbers. Colonies of Phaeocystis sp. were abundant along the NW Danish coast in April and May 1993. Autotrophic eukaryotic picoplankton occurred in cell numbers up to about 30 × 10 6 cells·dm −3 along the Swedish coast. The highest cell numbers of cyanobacteria of the Synechococcus-type, about 100 × 10 6 cells·dm −3, were found in the central Skagerrak in August and the abundance of Synechococcus was correlated with nitrogen uptake in the <3 μm size fraction.

Carbohydrates in the North Sea during spring blooms of Phaeocystis: a specific fingerprint

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 10:97-103 (1996) - doi:10.3354/ame010097 Carbohydrates in the North Sea during spring blooms of Phaeocystis: a specific fingerprint Janse I, van Rijssel M, Gottschal JC, Lancelot C, Gieskes WWC 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 um. 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. Phaeocystis . Mucus . Carbohydrates . Sugars Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 10, No. 1. Publication date: March 14, 1996 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1996 Inter-Research.

Nano- and Microplankton Dynamics during the Spring Phaeocystis Sp. Bloom in McMurdo Sound, Antarctica

The seasonal development of the microbial food web in eastern McMurdo Sound, Antarctica, was investigated during and immediately after the 1990–1991 bloom of Phaeocystis sp. (Prymnesiophyceae: Prymnesiales). From 23 November to 7 December, which was before the appearance of macroscopic colonies of Phaeocystis, both phytoplankton and Protozoa were low in abundance. During the Phaeocystis bloom (~10 December to 7 January), phytoplankton biomass was high and was dominated by colonial and singlecelled Phaeocystis, but other phytoplankton taxa, including diatoms and photosynthetic dinoflagellates, co-occurred. Heterotrophic nanoplankton and protozoan microzooplankton increased dramatically in biomass during the bloom. Non-thecate heterotrophic dinoflagellates were the most abundant microzooplankters. There was no evidence for inhibition of the microbial food web by Phaeocystis. By the post-bloom period, macroscopic colonies were rare and phytoplankton biomass had declined markedly. Microzooplankton biomass continued to rise until the end of the sampling period (23 January). Microfaecal pellets (median size range, 10–30 μm) were abundant during the bloom and post-bloom periods. In the post-bloom period, the heterotrophic protistan assemblage became very diverse, with numerous trophic linkages within the microbial food web. The abundance and diversity of the heterotrophic protist assemblage suggests that there was little control of protists by metazoans and that the microbial food web, consisting of bacteria, algae and Protozoa, was poorly coupled to metazoan zooplankton.

Nutrient-related selection mechanisms in marine phytoplankton communities and the impact of eutrophication on the planktonic food web

A general increase in nutrient discharges during the last few decades has caused various changes in the algal community structure along the European continental coast. Coincidentally and maybe consequently, the foodweb structure and functioning has altered in local areas causing various phenomena like oxygen depletion, mortality of groups of organisms, foam on beaches, and an increase in the productivity of benthic communities and some commercial fish species. The observed increases in algal biomass and shifts in species composition are discussed in relation to the involved key mechanisms: resource competition and selective grazing. Along the Dutch coastal zone of the North Sea eutrophication has caused a doubling of the yearly averaged algal biomass during the past three decades. The sudden appearance of Phaeocystis summer blooms coincided with a shift from P-limitation towards N-limitation in the Dutch coastal area due to a stronger increase in P-discharge relative to the increase in N-discharge. Competition experiments in continuous cultures showed Phaeocystis to become dominant under N-limitation. Additionally, the large Phaeocystis colonies, which can reach a diameter up to one centimetre, escape from microzooplankton grazing. A computer model is presented which demonstrates a shift from bottom-up towards top-down control if the pelagic environment becomes eutrophicated. Implementation of this concept in a size-differential phytoplankton control model generates the prediction that algal blooms are dominated by species that escape from grazing by those zooplankton species which have a high potential numerical response. In marine environments these are microzooplankton species. These organisms mainly feed on cyanobacteria, prochlorophytes and some nano-algal species. One of the consequences for foodweb structure and the carbon fluxes in marine foodwebs is that eutrophication will lead to the dominance of poorly edible algal species. Eutrophication favours the downward transport of carbon and nutrients towards the sediments not only due to higher algal biomasses but also as a consequence of a shift towards larger algal species with higher sedimentation characteristics. An example is given how these new insights can be used for water quality management purposes.

The mucilage phenomenon in the continental coastal waters of the North Sea

The basic mechanisms behind the mucilaginous phenomenon in the eutrophicated continental coastal waters of the North Sea are analysed in relation to observed short-term and predicted long-term quantitative and qualitative changes in riverine nutrient delivery to this coastal area. It is shown that foam accumulation observed every spring at sea surface and on the beaches, under windy conditions, results from food chain disruption due to the proliferation of one single phytoplanktonic species, the colony-forming Phaeocystis, peculiar physiology and biochemistry of which make them largely unpalatable for mesozooplankton and refractory to microbial degradation. Based on the knowledge of the carbon and nutrient metabolism of Phaeocystis colonies, making them more competitive than other phytoplankters to utilize nitrate as nitrogen source in dim coastal waters, it is concluded that the massive development of Phaeocystis colonies should have been enhanced by new sources of riverine nutrients, severely deficient in silicate and phosphate with respect to nitrogen and for which nitrate is the dominant form. Accordingly, historical and present-day records of bulky Phaeocystis colony blooms are closely related to those changes in land use and/or hydraulic and waste water managements that have led, over the last 100 years, to increased delivery of nitrates to the coastal area.

On the trophic fate of Phaeocystis pouchetii (hariot): VI. Significance of Phaeocystis-derived mucus for vertical flux

The development and decline of a phytoplankton spring bloom dominated by the prymnesiophyte Phaeocystis pouchetii were studied in Balsfjord, northern Norway between 30 March and 27 May 1992. At a fixed station, the concentration and composition of suspended particulate matter was monitored and compared to the particulate matter collected in sediment traps at six different depths. Direct sedimentation of phytoplankton contributed a minor fraction to particle flux and was confined to a few diatom genera. No evidence was found for pronounced aggregation of Phaeocystis colonies during bloom decline or direct sedimentation of either Phaeocystis colonies or single cells. Particle flux was dominated by faecal-pellet sedimentation during most of the study period, suggesting zooplankton grazing to be a main loss factor. Despite an abrupt decrease in faecal-pellet sedimentation after the decline of the bloom, particulate-carbon sedimentation rates remained high. High post-bloom sedimentation rates were characterized by elevated C/N and C/Chl a ratios of largely amorphous sedimented material. Post-bloom sedimentation coincided with a decrease in transparent exopolymeric particles (TEP) in the surface layer, suggesting that this change resulted from aggregation and sedimentation of carbon-rich exopolymeric material accumulated in the surface layer in the course of the bloom. While organic-carbon accumulation indicates the significance of disintegration of Phaeocystis colonies, post-bloom mucilage sedimentation could be secondary pathway for the vertical flux of Phaeocystis-derived organic matter.