Daily irradiance governs growth rate and colony formation of Phaeocystis (Prymnesiophyceae)

Phaeocystis was cultured at a range of ecologically significantdaily irradiances under nutrient-replete conditions. Below athreshold of 100 W h m^–1 day^–1, the cells were smalland flagellated, and remained solitary. Above this threshold,the cells were larger and able to form colonies. Growth rateand colony formation were maximum at sea surface irradiances(>700 W h m^–2 day^–2). Presumably, colonial growthis a strategy to maintain optimum growth rates in the watercolumn. Sinking, nutrient-stressed colonies reach low irradiancesand colonial cells can transform into small solitary flagellatedcells. These observations are important in understanding theecology and life cycle of Phaeocystis.     

Grazing and colony size development in Phaeocystis globosa (Prymnesiophyceae): the role of a chemical signal

The bloom-forming prymnesiophyte Phaeocystis globosa forms hollow,spherical, mucilaginous colonies that vary from micrometresto millimetres in size. A recent paper gave the first empiricalevidence that colony size increase in P. globosa is a defensiveresponse against grazers, and knowing the signalling mechanism(s)behind this response will thus be a key to understanding thetrophodynamics in systems dominated by this species. I conductedexperiments with specially designed diffusion incubators, eachof which consists of a non-grazing chamber (with P. globosaonly) and a grazing chamber (grazers + phytoplankton) connectedby 2 µm polycarbonate membrane filters. The results showedthat physical contact with grazers was not required to initiatethe defensive response; instead, P. globosa colony size increasewas found to be stimulated by dissolved chemicals generatedby ambient grazing activities. This signal was non-species specific,such that various combinations of three species of grazers andfour species of phytoplankton in the grazing chambers all resultedin significant, but different extents of colony enlargementin P. globosa in the non-grazing chambers (30–300% largerthan the ‘grazer-free’ control). High concentrationsof ambient solitary P. globosa cells and other phytoplanktonseemed to suppress colony enlargement in P. globosa, and grazerswould help reduce this inhibition by removing the ambient solitaryP. globosa cells and other phytoplankton. These non-species-specificmechanisms would allow P. globosa to regulate colony size developmentand defend itself in diverse planktonic systems, which may helpto explain the global success of this species.     

Colony size, cell number, carbon and nitrogen contents of Phaeocystis pouchetii from western Norway

Phaeocystis pouchetii is an ecologically important colony-formingmarine phytoplankton species in northern hemisphere cold waters.It plays a central role in the processing of biogeochemicallyimportant elements in the upper ocean during spring blooms.Here, we report highly significant quantitative relationshipsamong colony size, cell number and particulate carbon and nitrogencontents of field populations of P. pouchetii, which providethe means to quantitatively convert its biological expressioninto units of biogeochemical significance. Populations weresampled from mesocosms incubated in situ in western Norway andeither fertilized with nitrate and phosphate or left unamended.Phaeocystis colony blooms developed in both scenarios, but weremuch greater in fertilized treatments. Colonies from the lattertreatments were larger, contained higher concentrations of cellsand more particulate carbon and nitrogen than those in the unfertilizedmesocosm. Considering all data, log cell number increased linearlywith log colony volume with a slope of 0.54. Log carbon andnitrogen increased with log colony volume, with respective slopesof 0.92 and 1.22, indicating a significant component of non-cellularcarbon and nitrogen within the colonies. Carbon and nitrogencontents of colonies were linearly related, and fertilized coloniescontained more nitrogen relative to carbon than unfertilizedcolonies. These equations are particularly applicable to contemporarystudies of P. pouchetii because they represent colonies growingin environments that mimic a continuum from natural to eutrophicatedecosystems.     

Survival and recovery of Phaeocystis antarctica (Prymnesiophyceae) from prolonged darkness and freezing

The colony-forming haptophyte Phaeocystis antarctica is an important primary producer in the Ross Sea, and must survive long periods of darkness and freezing temperature in this extreme environment. We conducted experiments on the responses of P. antarctica-dominated phytoplankton assemblages to prolonged periods of darkness and freezing. Chlorophyll and photosynthetic capacity of the alga declined nonlinearly and independently of each other in the dark, and darkness alone would potentially reduce photosynthetic capacity by only 60 per cent over 150 days (approximately the length of the Antarctic winter in the southern Ross Sea). The estimated reduction of colonial mucous carbon is higher than that of colonial cell carbon, suggesting metabolism of the colonial matrix in the dark. The alga quickly resumed growth upon return to light. Phaeocystis antarctica also survived freezing, although longer freezing durations lengthened the lag before growth resumption. Particulate dimethylsulfoniopropionate relative to chlorophyll increased upon freezing and decreased upon darkness. Taken together, the abilities of P. antarctica to survive freezing and initiate growth quickly after darkness may provide it with the capability to survive in both the ice and the water column, and help explain its repeated dominance in austral spring blooms in the Ross Sea and elsewhere in the Southern Ocean.     

Growth and mortality of flagellates and non-flagellate cells of Phaeocystis globosa (Prymnesiophyceae)

Two cell types of the same clone of Phaeocystis globosa, solitarynon-flagellate cells and flagellates, were grown in batch culturesunder identical conditions. The non-flagellate cells had a shorterlag phase (1.4 versus 2.8 days) and a higher growth rate (0.72versus 0.65 day^–1) than flagellate cells. The flagellateshad a longer stationary phase (15.6 versus 9.5 days) and a lowerdeath rate (0.07 versus 0.52 day^–1) than non-flagellatecells. All differences were statistically significant. Biomassyield did not differ between the two cell types. The short lagphase and high growth rate of nonflagellate cells correspondsto field observations of rapidly developing non-flagellate Phaeocystisblooms that are typically observed in nutrient-rich environmentssuch as temperate seas in spring. The flagellate cell type,with its longer stationary phase and lower death rate than non-flagellatecells, is better equipped for survival in oligotrophic environments.This explains why the flagellates of Phaeocystis are abundantafter the spring phytoplankton bloom in temperate seas and inother nutrient-poor environments such as the open ocean.     

The colonization of two Phaeocystis species (Prymnesiophyceae) by pennate diatoms and other protists: a significant contribution to colony biomass

The association of Phaeocystis spp. with small pennate diatoms during three Phaeocystis-dominated spring blooms were investigated in the Eastern English Channel (2003 and 2004) and in coastal waters of Western Norway during a mesocosm experiment (2005). In each of these studies, colonization of the surface of large Phaeocystis spp. colonies by small needle-shaped diatoms (Pseudo-nitzschia spp.) were observed. In the English Channel the diatom Pseudo-nitzschia delicatissima colonized the surface of large (>100 μm) Phaeocystis globosa colonies. The abundance of Pseudo-nitzschia delicatissima reached 130 cells per colony and formed up to 70% of the total carbon associated with Phaeocystis cells during late bloom stages. In Norwegian waters, the surface of large (>250 μm) Phaeocystis pouchetii colonies were colonized by Pseudo-nitzschia cf. granii var. curvata and to a lesser degree by other phytoplankton and protist species, although the abundance of these diatoms was never greater than 40 cells per colony. Based on these observations we suggest that diatoms utilize Phaeocystis colonies not only as habitat, but that they are able to utilize the colonial matrix as a growth substrate. Furthermore, these observations indicate that a considerable fraction of biomass (chlorophyll) associated with Phaeocystis colonies, especially large colonies concerned with intense and prolonged blooms, are due to co-occurring plankton species and not exclusively Phaeocystis cells.     

Effect of PAR irradiance intensity on Phaeocystis antarctica (Prymnesiophyceae) growth and DMSP,DMSO, and acrylate concentrations

Phaeocystis antarctica forms extensive spring blooms in the Southern Ocean that coincide with high concentrations of dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO), dimethylsulfide (DMS), and acrylate. We determined how concentrations of these compounds changed during the growth of axenic P. antarctica cultures exposed to light-limiting, sub-saturating, and saturating PAR irradiances. Cellular DMSP concentrations per liter cell volume (CV) ranged between 199 and 403 mmol · L_CV⁻¹, with the highest concentrations observed under light-limiting PAR. Cellular acrylate concentrations did not change appreciably with a change in irradiance level or growth, ranging between 18 and 45 mmol · L_CV⁻¹, constituting an estimated 0.2%–2.8% of cellular carbon. Both dissolved acrylate and DMSO increased substantially with irradiance during exponential growth on a per-cell basis, ranging from 0.91 to 3.15 and 0.24 to 1.39 fmol · cell⁻¹, respectively, indicating substantial export of these compounds into the dissolved phase. Average cellular DMSO:DMSP ratios increased 7.6-fold between exponential and stationary phases of batch growth, with a 3- to 13-fold increase in cellular DMSO likely formed from abiotic reactions of DMSP and DMS with reactive oxygen species (ROS). At mM levels, cellular DMSP and acrylate are proposed to serve as de facto antioxidants in P. antarctica not regulated by oxidative stress or changes in ROS. Instead, cellular DMSP concentrations are likely controlled by other physiological processes including an overflow mechanism to remove excess carbon via acrylate, DMS, and DMSO during times of unbalanced growth brought on by physical stress or nutrient limitation. Together, these compounds should aid P. antarctica in adapting to a range of PAR irradiances by maintaining cellular functions and reducing oxidative stress.     

Isolation and phylogenetic analysis of novel viruses infecting the phytoplankton Phaeocystis globosa (Prymnesiophyceae)

Viruses infecting the harmful bloom-causing alga Phaeocystis globosa (Prymnesiophyceae) were readily isolated from Dutch coastal waters (southern North Sea) in 2000 and 2001. Our data show a large increase in the abundance of putative P. globosa viruses during blooms of P. globosa, suggesting that viruses are an important source of mortality for this alga. In order to examine genetic relatedness among viruses infecting P. globosa and other phytoplankton, DNA polymerase gene (pol) fragments were amplified and the inferred amino acid sequences were phylogenetically analyzed. The results demonstrated that viruses infecting P. globosa formed a closely related monophyletic group within the family Phycodnaviridae, with at least 96.9% similarity to each other. The sequences grouped most closely with others from viruses that infect the prymnesiophyte algae Chrysochromulina brevifilum and Chrysochromulina strobilus. Whether the P. globosa viruses belong to the genus Prymnesiovirus or form a separate group needs further study. Our data suggest that, like their phytoplankton hosts, the Chrysochromulina and Phaeocystis viruses share a common ancestor and that these prymnesioviruses and their algal host have coevolved.     

Isolation and Phylogenetic Analysis of Novel Viruses Infecting the Phytoplankton Phaeocystis globosa (Prymnesiophyceae)

Viruses infecting the harmful bloom-causing alga Phaeocystis globosa (Prymnesiophyceae) were readily isolated from Dutch coastal waters (southern North Sea) in 2000 and 2001. Our data show a large increase in the abundance of putative P. globosa viruses during blooms of P. globosa, suggesting that viruses are an important source of mortality for this alga. In order to examine genetic relatedness among viruses infecting P. globosa and other phytoplankton, DNA polymerase gene (pol) fragments were amplified and the inferred amino acid sequences were phylogenetically analyzed. The results demonstrated that viruses infecting P. globosa formed a closely related monophyletic group within the family Phycodnaviridae, with at least 96.9% similarity to each other. The sequences grouped most closely with others from viruses that infect the prymnesiophyte algae Chrysochromulina brevifilum and Chrysochromulina strobilus. Whether the P. globosa viruses belong to the genus Prymnesiovirus or form a separate group needs further study. Our data suggest that, like their phytoplankton hosts, the Chrysochromulina and Phaeocystis viruses share a common ancestor and that these prymnesioviruses and their algal host have coevolved.     

Molecular evidence identifies bloom-forming Phaeocystis (Prymnesiophyta) from coastal waters of southeast China as Phaeocystis globosa

Sequence data from the 18S small subunit ribosomal RNA gene have been used to identify the species of a Phaeocystis (Prymnesiophyta) that caused harmful algae blooms in the coastal waters of southeast China. This Phaeocystis has morphological and physiological features that differ from those previously described for either P. globosa Scherffel or P. pouchetii (Hariot) Lagerheim. However, the sequence comparison of the Phaeocystis 18S rDNA clearly showed that it was remarkably similar to several isolates of P. globosa. Thus, the species isolated from the southeast coast of China is identified as P. globosa rather than P. cf. pouchetii or another species. Our results also demonstrate that phenotypes of different members of the genus Phaeocystis are variable, apparently changing in response to environmental conditions. It is concluded that, on the basis of this phylogenetic analysis, the bloom forming southeast China coast species of Phaeocystis most likely originated from an endemic warm-water, rather than a foreign source.     

Molecular genetic delineation of Phaeocystis species (Prymnesiophyceae) using coding and non-coding regions of nuclear and plastid genomes

Sequence variation among 22 isolates representing a global distribution of the prymnesiophyte genus Phaeocystis has been compared using nuclear-encoded 18S rRNA genes and two non-coding regions: the ribosomal DNA internal transcribed spacer 1 (ITS1) separating the 18S rRNA and 5.8S rRNA genes and the plastid ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) spacer flanked by short stretches of the adjacent large and small subunits (rbcL and rbcS). 18S rRNA can only resolve major species complexes. The analysis suggests that an undescribed unicellular Phaeocystis sp. (isolate PLY 559) is a sister taxon to the Mediterranean unicellular Phaeocystis jahnii; this clade branched prior to the divergence of all other Phaeocystis species, including the colonial ones. Little divergence was seen among the multiple isolates sequenced from each colonial species complex. RUBISCO spacer regions are even more highly conserved among closely related colonial Phaeocystis species and are identical in Phaeocystis antarctica, Phaeocystis pouchetii and two warm-temperate strains of Phaeocystis globosa, with a single base substitution in two cold-temperate strains of P. globosa. The RUBISCO spacer sequences from two predominantly unicellular Phaeocystis isolates from the Mediterranean Sea and PLY 559 were clearly different from other Phaeocystis strains. In contrast, ITS1 exhibited substantial inter- and intraspecific sequence divergence and showed more resolution among the taxa. Distinctly different copies of the ITS1 region were found in P. globosa, even among cloned DNA from a single strain, suggesting that it is a species complex and making this region unsuitable for phylogenetic analysis in this species. However, among nine P. antarctica strains, four ITS1 haplotypes could be separated. Using the branching order in the ITS1 tree we have attempted to trace the biogeographic history of the dispersal of strains in Antarctic coastal waters.     

On the trophic fate of Phaeocystis pouchetii (Harlot). III. Functional responses in grazing demonstrated on juvenile stages of Calanus finmarchicus (Copepoda) fed diatoms and Phaeocystis

The objective of this study was to quantify the functional responsein feeding rate in the various developmental stages of Calanusfinmarchicus to different concentrations of the diatoms Thalassiosiranordenskioeldii and Porosira glacialis, and the haptophyseanPhaeocystis pouchetii. Grazing of copepodite stage I–VC.finmarchicus was measured using two different approaches.Feeding rates were obtained from either incubation experiments,estimating the rate of removal of particles from suspension,or by quantifying the turnover rate of the plant pigments inthe gut. Clearance as a function of algal concentration (1–30µg plant pigment 1^–1) was described in juvenilestages of C.finmarchicus fed the diatoms T.nordenskioeldii [20µm equivalent spherical diameter (ESD)], P.glacialis (40µm ESD), and two size categories (30–100 µmand >100 µm ESD) of the gelatinous alga P.pouchetii.When the copepodite stages were fed T.nordenskioeldii, the gutcontent of plant pigments was in general higher than when fedP.glacialis. Rates obtained were variable when the same copepoditestages were offered the two size categories of P.pouchetii,but within the same order of magnitude as those obtained forthe larger diatom. At unialgal diets, diatoms were more readilyconsumed than the larger size fraction among colonies of P.pouchetiiby copepodite stage I–III C.finmarchicus. But given anappropriate prey size, C.finmarchicus grazed both diatoms andcolonies of gelatinous algae at equal rates. A linear relationshipbetween gut content and food concentrations <10 µgchlorophyll 1^–1 was found. This indicates that the ingestionrate in C.finmarchicus is directly proportional to the ambientfood concentration during the most productive period in Mayand June in high latitudes irrespective of algal species present. ¹Present address: Marine Biological Laboratory, University ofCopenhagen, Strandpromenaden 5, DK-3000 Helsingør, Denmark ²Present address: Greater Copenhagen Council, Gl. KøgeLandevej 1–3, DK-2550 Valby, Denmark     

A mesocosm study of Phaeocystis globosa (Prymnesiophyceae) population dynamics: II. Significance for the microbial community

The impact of Phaeocystis globosa population decline on the microbial community was studied during a mesocosm experiment, with irradiance regime and inorganic N:P ratios (4, 16, and 44) as controlling factors. Heterotrophic bacterial activity was closely related to enhanced (viral) lysis rates of P. globosa cells and disintegration of the colonies. Up to 85% of the bacterial C demand could be supplied by P. globosa-specific cellular C release. The bacterial populations with high DNA content became dominant (>70% of total). The bacterial community showed a rapid shift in composition to take advantage of the changing conditions during the demise of the P. globosa bloom. Members of the Alphaproteobacteria and the Bacteroidetes group emerged directly upon bloom decay. Multidimensional scaling analysis in conjunction with DGGE fingerprinting implied that clustering was more related to the availability of organic carbon (the collapse of the P. gobosa bloom) than to the nature of the phytoplankton growth-controlling nutrient. Reduced irradiance delayed the development of the P. globosa population and subsequently changes in the bacterial community composition. Disintegration of P. globosa colonies resulted in the formation of transparent exopolymeric particles (TEP) and aggregates, more so under P-depletion than under N-deficient conditions. The colonial matrix transformed into big aggregates under P-depleted conditions but remained largely as ghost colonies under N-depleted conditions. In the mesocosm with initial nitrogen and phosphorus supplied in the Redfield ratio, features intermediate to conditions with either N- or P-depletion were observed. It was hypothesized that TEP affected microbial population dynamics directly through bacterial colonization and indirectly through scavenging of predators and viruses.     

Toxic cyanobacteria strains isolated from blooms in the Guadiana river (southwestern Spain)

This paper describes the occurrence of toxic cyanobacteria along the Guadiana River over its course between Mérida and Badajoz (Extremadura, Spain). Water sampling for phytoplankton quantification and toxin analysis was carried out regularly between 1999 and 2001 in six different locations, including two shallow, slow-flowing river sites, two streamed river sites and two drinking water reservoirs. The cyanobacterial community differed significantly between these locations, especially during the summer. The predominant genera were Microcystis, Oscillatoria, Aphanizomenon and Anabaena. Using an ELISA assay the total microcystin contents of natural water samples from the most eutrophic locations ranged from 0.10 - 21.86 microg mcyst-LR equivalent x L(-1) in Valdelacalzada and 0.10-11.3 microg mcyst-LR equivalent x L(-1) in Vitonogales, and a seasonal variation of toxin content was observed. The amount of microcystins produced by each strain was determined by ELISA assay and the detection and identification of microcystin variants of three toxic strains of Microcystis aeruginosa was performed by high performance liquid chromatography (HPLC). The analysis of microcystins of the cultured strains revealed that toxin production was variable among different strains of M. aeruginosa isolated either from different blooms or from the same bloom.     

Observations of flagellates in colonies of Phaeocystis globosa (Prymnesiophyceae); a hypothesis for their position in the life cycle

Flagellates of Phaeocystis globosa were observed inside coloniesin North Sea samples in 1992. Field data suggest that low phosphateconcentrations (     

Effects of small-scale turbulence on Phaeocystis globosa (Prymnesiophyceae) growth and life cycle

The response of Phaeocystis globosa to small-scale turbulence was studied in 5 l microcosms. Turbulence was generated by oscillating grids. The effect of small-scale turbulence was examined under 3 turbulence levels representative of the P. globosa natural environment, and in non-turbulent control cultures. Single cell numbers, nitrogen concentrations and colony formation (number and diameter) were followed over 13 days in each experimental culture. Small-scale turbulence decreased single cell growth and also influenced colony formation. More colonies were formed when turbulence increased to a given threshold, but above this turbulence level, fewer and smaller colonies were observed in P. globosa cultures. The ecological significance of these results, particularly, the potential influence of small-scale turbulence on competition mechanisms between P. globosa and diatoms are finally discussed and suggested as a key factor to understand phytoplankton successions in the Eastern English Channel.     

JAX Colony Management System (JCMS): an extensible colony and phenotype data management system

The Jackson Laboratory Colony Management System (JCMS) is a software application for managing data and information related to research mouse colonies, associated biospecimens, and experimental protocols. JCMS runs directly on computers that run one of the PC Windows^® operating systems, but can be accessed via web browser interfaces from any computer running a Windows, Macintosh^®, or Linux^® operating system. JCMS can be configured for a single user or multiple users in small- to medium-size work groups. The target audience for JCMS includes laboratory technicians, animal colony managers, and principal investigators. The application provides operational support for colony management and experimental workflows, sample and data tracking through transaction-based data entry forms, and date-driven work reports. Flexible query forms allow researchers to retrieve database records based on user-defined criteria. Recent advances in handheld computers with integrated barcode readers, middleware technologies, web browsers, and wireless networks add to the utility of JCMS by allowing real-time access to the database from any networked computer.     

Impact of macroalgal blooms and wader predation on intertidal macroinvertebrates: experimental evidence from the Mondego estuary (Portugal)

The effect of macroalgal blooms and predation by wading on benthic macroinvertebrates was examined in the Mondego estuary, Portugal, during spring 1997. Introduced macroalgal cover and exclusion of predators were used to examine changes in density of macroinvertebrates using univariate and multivariate analyses. There was no evidence of changes in numbers of macroinvertebrates due to predation. Macroalgae were, however, responsible for a decrease in abundance of the worms Amage adspersa (Grube) and Streblospio shrubsolii (Buchanan), and a substantial increase in numbers of Capitella capitata (Fabricius). The density of the worm Hediste diversicolor (O.F. Müller) increased during the first month and decreased after 2 months, associated with macroalgal cover. There were no differences in abundances of macroinvertebrates between different depths. Overall, only polychaete species were affected by macroalgae. Multivariate analysis also showed clear differences in assemblages of macroinvertebrates due to the presence of macroalgae.