高摄食压力下球形棕囊藻凝聚体的形成

棕囊藻包含囊体和游离单细胞两种生活史阶段。囊体是棕囊藻藻华爆发时的优势形态,藻华衰退时囊体能够形成凝聚体,但是棕囊藻游离单细胞的凝聚体极少被发现。本次研究将球形棕囊藻单细胞和高密度的海洋弯曲甲藻共同培养,使球形棕囊藻的生长承受高摄食压力,通过观察摄食者和棕囊藻的生长、凝聚体的数量和形态,阐明单细胞凝聚体的形成以及与摄食压力的关系。当球形棕囊藻进入衰退期时,高摄食压力引发游离单细胞聚合形成凝聚体,无摄食压力情况下,单细胞不形成凝聚体。凝聚体由无鞭毛细胞组成,细胞排列紧密,近似球体。凝聚体形成伊始,凝聚体内部可见凝胶状物质将细胞互相粘结,并且粘附了纤维等物质。凝聚体的体积和粘附的细胞数量逐渐提高,细胞排列愈加紧密,凝聚体内部形态和结构不易分辨。凝聚体的形成有效保护了部分单细胞免受摄食压力的影响,减少了摄食死亡率。凝聚体的形成是球形棕囊藻面临高摄食压力时采取的主动的防御策略。球形棕囊藻能够频繁引发大规模藻华的原因可能在于其在生长的各个阶段中均具有优越的竞争策略。     

DIMETHYLSULFONIOPROPIONATE STORAGE IN PHAEOCYSTIS (PRYMNESIOPHYCEAE) SECRETORY VESICLES1

Despite the global importance of dimethylsulfoniopropionate (DMSP)/dimethyl sulfide (DMS) and their role in climate regulation, little is known about the mechanisms of their production and storage in Phaeocystis sp., a major contributor of DMS in polar areas. Phaeocystis secretes polymer microgels, by regulated exocytosis, remaining in condensed phase while stored in secretory vesicles ( Chin et al. 2004 ). In secretory cells, vesicles also store small molecules, which are released during exocytosis. Here, we demonstrated that DMSP and DMS were stored in the secretory vesicles of Phaeocystis antarctica G. Karst. They were trapped within a polyanionic gel matrix, which prevented an accurate measurement of their concentration in the absence of a chelating agent such as EDTA. Understanding the production and the export mechanisms of DMSP and DMS into seawater is important because of the impact the cellular and extracellular pools of these highly relevant biogeochemical metabolites have on the environment. The pool of total DMSP in the presence of Phaeocystis may be underestimated by as much as half. Obtaining accurate budget measurements is the first step toward gaining a better understanding of key issues related to the DMS ocean–air interaction and the effect of phytoplankton DMS production on climate change.     

Compositional changes in neurotoxins and their oxidative derivatives from the dinoflagellate, Karenia brevis, in seawater and marine aerosol

The harmful alga, Karenia brevis, produces a suite of polyether neurotoxins, brevetoxins or PbTx, that cause marine animal mortality and neurotoxic shellfish poisoning (NSP). A characteristic of K. brevis blooms is associated airborne toxins that result in severe respiratory problems. This study was undertaken to determine the composition of aerosolized brevetoxins and oxidative derivatives to which beachgoers are exposed during a K. brevis bloom. The suite of brevetoxins and derivatives in seawater is comprised of intra-cellular (IC) and extra-cellular (EC) compounds. We hypothesized that aerosolized compounds are generated primarily from EC, hydrophobic compounds in seawater by bubble-mediated transport. Thus the composition of aerosolized brevetoxins and derivatives, to which beachgoers are exposed, would reflect the EC composition of the source matrix (the local surf zone). Brevetoxins were extracted from water collected along the shore and from marine aerosols along Siesta Beach and Lido Beach in Sarasota, FL, USA, during K. brevis blooms. Water samples were further processed into IC and EC components. The primary brevetoxins observed in water and air included PbTx-1, -2, -3, -PbTx-2-carboxylic acid, and brevenal. Oxidation and/or hydrolysis products of PbTx-1, -2, -3 and -7 were also found in EC water and in aerosol, but not IC.     

Short-term changes in polysaccharide utilization mechanisms of marine bacterioplankton during a spring phytoplankton bloom

Spring phytoplankton blooms in temperate environments contribute disproportionately to global marine productivity. Bloom-derived organic matter, much of it occurring as polysaccharides, fuels biogeochemical cycles driven by interacting autotrophic and heterotrophic communities. We tracked changes in the mode of polysaccharide utilization by heterotrophic bacteria during the course of a diatom-dominated bloom in the German Bight, North Sea. Polysaccharides can be taken up in a ‘selfish’ mode, where initial hydrolysis is coupled to transport into the periplasm, such that little to no low-molecular weight (LMW) products are externally released to the environment. Alternatively, polysaccharides hydrolyzed by cell-surface attached or free extracellular enzymes (external hydrolysis) yield LMW products available to the wider bacterioplankton community. In the early bloom phase, selfish activity was accompanied by low extracellular hydrolysis rates of a few polysaccharides. As the bloom progressed, selfish uptake increased markedly, and external hydrolysis rates increased, but only for a limited range of substrates. The late bloom phase was characterized by high external hydrolysis rates of a broad range of polysaccharides and reduced selfish uptake of polysaccharides, except for laminarin. Substrate utilization mode is related both to substrate structural complexity and to the bloom-stage dependent composition of the heterotrophic bacterial community.     

Bacteria immobilised in Gels: Improved methodologies for antifouling and biocontrol applications

A range of bacteria, including the marine bacterium Pseudoalteromonas tunicata which produces antifouling compounds, and Escherichia coli were used to investigate methods for immobilising bacteria in gels. Different types of matrices were screened using the survival of barnacle nauplii as a bioassay. A Dupont? polyvinylalcohol (PVOH) 10% gel was found to be the optimal matrix. This non-toxic gel remained stable in seawater while allowing for an outflux of active biological compounds from the bacterial cells. The presence of active bacterial cells in the matrix was tested by CTC-staining, green fluorescent protein (GFP) expressing bacteria and a barnacle larvae bioassay. The Dupont? PVOH 10% gels containing P. tunicata cells were inhibitory against larvae for a period of up to 2 weeks. In further studies using gels containing immobilised bacteria, the E. coli strain C600 was employed based on its cell size, stress resistance and the fact that a plasmid for the expression of GFP could be transferred and maintained in the cells. Immobilised E. Coli cells maintained their viability in the Dupont? PVOH 10% gels for as long as 2 months, and the life-span of these "biologically active"; gels was increased to more than 2 months by the incorporation of small beads into the gels. The results indicate that bacteria can be immobilised in coatings for periods of time consistent with the needs of some antifouling and antibacterial applications.     

Satellite discrimination of Karenia mikimotoi and Phaeocystis harmful algal blooms in European coastal waters: Merged classification of ocean colour data

The detection of dense harmful algal blooms (HABs) by satellite remote sensing is usually based on analysis of chlorophyll-a as a proxy. However, this approach does not provide information about the potential harm of bloom, nor can it identify the dominant species. The developed HAB risk classification method employs a fully automatic data-driven approach to identify key characteristics of water leaving radiances and derived quantities, and to classify pixels into “harmful”, “non-harmful” and “no bloom” categories using Linear Discriminant Analysis (LDA). Discrimination accuracy is increased through the use of spectral ratios of water leaving radiances, absorption and backscattering. To reduce the false alarm rate the data that cannot be reliably classified are automatically labelled as “unknown”. This method can be trained on different HAB species or extended to new sensors and then applied to generate independent HAB risk maps; these can be fused with other sensors to fill gaps or improve spatial or temporal resolution. The HAB discrimination technique has obtained accurate results on MODIS and MERIS data, correctly identifying 89% of Phaeocystis globosa HABs in the southern North Sea and 88% of Karenia mikimotoi blooms in the Western English Channel. A linear transformation of the ocean colour discriminants is used to estimate harmful cell counts, demonstrating greater accuracy than if based on chlorophyll-a; this will facilitate its integration into a HAB early warning system operating in the southern North Sea.     

Using HPLC pigment analysis to investigate phytoplankton taxonomy: the importance of knowing your species

Phytoplankton microscopic enumerations and HPLC analyses of their pigments were performed weekly for a complete year at a coastal station in the English Channel. The taxonomic composition of the phytoplankton community was assessed using the HPLC results combined with the mathematical tool CHEMTAX in two different ways. Firstly, without using the species level taxonomic information obtained at the microscopic level (blind analyses), and secondly by including the information from the microscopic taxonomic analysis (directed analyses). The results indicate that, due to the particular pigment composition of some species (for example, the dinoflagellate, Karenia mikimotoi and the haptophyte, Phaeocystis pouchetii), a blind analysis would result in very significant errors in the taxonomic determination of the bloom events at this station. Major blooms of Karenia mikimotoi and P. pouchetii were mistaken for blooms of diatoms on the basis of a blind HPLC-CHEMTAX analysis. Only with the information from the microscopic observations was it possible to obtain an accurate representation of the phytoplankton community.Communicated by H.-D. Franke     

Zooplankton feeding ecology: does a diet of Phaeocystis support good copepod grazing, survival, egg production and egg hatching success?

The bloom-forming alga Phaeocystis is ingested by a varietyof zooplankton grazers, but is thought to be a poor source offood. We examined copepod grazing on solitary Phaeocystis cellsby adult females of Temora stylifera, and survival, fecal pelletproduction, egg production and egg hatching success in Calanushelgolandicus and T. stylifera over periods of 15 consecutivedays. Phaeocystis cell concentrations were high (1.2–3.6x 10⁴ cells ml^–1 for C. helgolandicus and 2.5–7.9x 10⁴ cells ml^–1 for T. stylifera), but within the rangeof maxima recorded for natural blooms. Both copepods survivedwell and continuously produced fecal pellets (indicating continuousgrazing) on a diet of Phaeocystis. However, egg production ratesfor both copepods were low, even though hatching success ofthe few eggs produced was high. Clearance rates for T. styliferawere higher than for most previous measurements of other copepodsfeeding on Phaeocystis solitary cells at lower cell concentrations.We conclude that even though copepods feed well upon Phaeocystis,resulting poor fecundity on this diet may inhibit copepod populationincreases during blooms, thereby contributing to the perpetuationof blooms. However, the high egg hatching success on this dietargues against Phaeocystis containing chemical compounds thatact as mitotic inhibitors reducing copepod egg viability, suchas those found in some other phytoplankters.     

2000～2001年粤东柘林湾营养盐分布

2000年5月-2001年5月对粤东大规模增养殖区柘林湾及湾外附近海域进行了大量营养盐,浮游生物和一般理化因子的周年调查。结果表明,调查海域溶解性无机氮,磷,硅含量都明显偏高,年平均值分别达到22.64,1.95和59.7μmol/L,其中,氮,磷含量均超过国家三类海水的水质标准,由于湾顶黄冈河和湾周边排污排废的影响,营养盐的分布基本表现为由湾内向湾外,近岸向离岸递减的格局,大规模增养殖业造成的2次污染对该湾营养盐的时空分布具有重要的影响,柘林湾氮,磷,硅含量虽全面偏高,但如以Justic和Dortch等的标准来衡量,该湾浮游植物生长受控于单一营养盐限制因子的出现率为氮41.75%,磷22.9%,硅2.36%。     

2000～2001年柘林湾浮游植物群落结构及数量变动的周年调查

2000年5月－2001年5月对粤东赤潮重灾区柘林湾者的浮游植物周年调查表明,柘林湾共有浮游植物54属153种。其中硅藻为优势类群,共37属114种,占总种数的74.51%;甲藻15属36种;其它2属3种。浮游植物种数和丰度的平面分布表现为弯内低于湾外,东部低于西部的基本格局,季节波动模式则为单峰型,全年数量最高峰位于盛夏7月份。中肋骨条藻（Skeletonema costatum）为该湾的全年优势种,在群落总细胞数中的百分比年平均高达58.7%。通过对水温、营养盐、浮激植物群落的多样性指数和均匀度以及中肋骨务藻的种群密度等相互之间的回归分析,并考虑增养殖渔业等因素,发现柘林湾因大规模增养殖渔业和高强度的排污排废引志的富营养化已在很大程度上改变了该湾浮游植物的群落结构及时空分布,使生物多样性与均匀度明显下降,中肋骨条藻等少数种类则大量增殖,硅藻赤潮,尤其是中肋骨条藻赤潮的发生机会明显增多,但发生甲藻赤潮的可能性较小。     

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.     

2000～2001年柘林湾浮游动物的群落结构及时空分布

20 0 0年 7月至 2 0 0 0 1年 7月的周年调查结果表明 ,粤东柘林湾浮游动物有桡足类 2 9属 5 7种 ,枝角类 3属 3种 ,及端足类、磷虾、糠虾、多毛类、毛颚类、被囊类、水母和各种浮游幼体。其中 ,强额拟哲水蚤 Paracalanuscrassirostris、短角长腹剑水蚤 Oithona brevicornis和鸟喙尖头 Penilia avirostris为优势种 ,合计占浮游动物总个体数的 6 2 .7%。浮游动物的种类数、生物量和总个体数都表现为湾外大于湾内的平面分布格局 ,周年变化基本上为单峰型 ,高峰期位于 6～ 1 0月份 ,最低谷位于冬季 1月份。因此 ,总个体数与水温成显著正相关关系。柘林湾是一个浮游动物相对丰富的海湾 ,年均生物量为 1 1 5 .7mg· dw / m3 ,总个体数达 6 .8× 1 0 3 ind/ m3 ,但群落结构的小型化趋势比较明显。回归分析结果表明 ,浮游动物总个体数与浮游植物密度成显著正相关关系。     

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.     

Long-term development of the crustacean plankton in the Saidenbach Reservoir (Germany) – changes,causes, consequences

The rates of development and food intake of the copepod Temora longicornis (Müller) were studied using artificial blooms of Phaeocystis globosa Scherffel under different conditions of nutrient limitation. Mesocosms with 800 l of natural seawater were manipulated by inoculation with cultured P. globosa and by addition of nitrogen and/or phosphorus, to obtain N- or P-limited blooms of P. globosa. During development and ageing of these blooms, water from the mesocosms was used as medium for incubation of nauplii of T. longicornis. Only moderate rates of naupliar development as well as high rates of mortality were observed, irrespective of major differences of nutrient conditions and density of P. globosa. Grazing by the nauplii on P. globosa seemed to be low, suggesting a low food quality of this alga at all physiological conditions studied. The results of this study indicate a low capability of T. longicornis nauplii for control of nuisance algal blooms caused by P. globosa.     

Effect of melting Antarctic sea ice on the fate of microbial communities studied in microcosms

Although algal growth in the iron-deficient Southern Ocean surface waters is generally low, there is considerable evidence that winter sea ice contains high amounts of iron and organic matter leading to ice-edge blooms during austral spring. We used field observations and ship-based microcosm experiments to study the effect of the seeding by sea ice microorganisms, and the fertilization by organic matter and iron on the planktonic community at the onset of spring/summer in the Weddell Sea. Pack ice was a major source of autotrophs resulting in a ninefold to 27-fold increase in the sea ice-fertilized seawater microcosm compared to the ice-free seawater microcosm. However, heterotrophs were released in lower numbers (only a 2- to 6-fold increase). Pack ice was also an important source of dissolved organic matter for the planktonic community. Small algae (<10 μm) and bacteria released from melting sea ice were able to thrive in seawater. Field observations show that the supply of iron from melting sea ice had occurred well before our arrival onsite, and the supply of iron to the microcosms was therefore low. We finally ran a “sequential melting” experiment to monitor the release of ice constituents in seawater. Brine drainage occurred first and was associated with the release of dissolved elements (salts, dissolved organic carbon and dissolved iron). Particulate organic carbon and particulate iron were released with low-salinity waters at a later stage.     

Microbial community composition and function in permanently cold seawater and sediments from an arctic fjord of svalbard

Heterotrophic microbial communities in seawater and sediments metabolize much of the organic carbon produced in the ocean. Although carbon cycling and preservation depend critically on the capabilities of these microbial communities, their compositions and capabilities have seldom been examined simultaneously at the same site. To compare the abilities of seawater and sedimentary microbial communities to initiate organic matter degradation, we measured the extracellular enzymatic hydrolysis rates of 10 substrates (polysaccharides and algal extracts) in surface seawater and bottom water as well as in surface and anoxic sediments of an Arctic fjord. Patterns of enzyme activities differed between seawater and sediments, not just quantitatively, in accordance with higher cell numbers in sediments, but also in their more diversified enzyme spectrum. Sedimentary microbial communities hydrolyzed all of the fluorescently labeled polysaccharide and algal extracts, in most cases at higher rates in subsurface than surface sediments. In seawater, in contrast, only 5 of the 7 polysaccharides and 2 of the 3 algal extracts were hydrolyzed, and hydrolysis rates in surface and deepwater were virtually identical. To compare bacterial communities, 16S rRNA gene clone libraries were constructed from the same seawater and sediment samples; they diverged strongly in composition. Thus, the broader enzymatic capabilities of the sedimentary microbial communities may result from the compositional differences between seawater and sedimentary microbial communities, rather than from gene expression differences among compositionally similar communities. The greater number of phylum- and subphylum-level lineages and operational taxonomic units in sediments than in seawater samples may reflect the necessity of a wider range of enzymatic capabilities and strategies to access organic matter that has already been degraded during passage through the water column. When transformations of marine organic matter are considered, differences in community composition and their different abilities to access organic matter should be taken into account.     

Summer diatom blooms in the North Pacific subtropical gyre: 2008-2009

The summertime North Pacific subtropical gyre has widespread phytoplankton blooms between Hawaii and the subtropical front (～30°N) that appear as chlorophyll (chl) increases in satellite ocean color data. Nitrogen-fixing diatom symbioses (diatom-diazotroph associations: DDAs) often increase 10(2)-10(3) fold in these blooms and contribute to elevated export flux. In 2008 and 2009, two cruises targeted satellite chlorophyll blooms to examine DDA species abundance, chlorophyll concentration, biogenic silica concentration, and hydrography. Generalized observations that DDA blooms occur when the mixed layer depth is < 70 m are supported, but there is no consistent relationship between mixed layer depth, bloom intensity, or composition; regional blooms between 22-34°N occur within a broader temperature range (21-26°C) than previously reported. In both years, the Hemiaulus-Richelia and Rhizosolenia-Richelia DDAs increased 10(2)-10(3) over background concentrations within satellite-defined bloom features. The two years share a common trend of Hemiaulus dominance of the DDAs and substantial increases in the >10 μm chl a fraction (～40-90+% of total chl a). Integrated diatom abundance varied 10-fold over <10 km. Biogenic silica concentration tracked diatom abundance, was dominated by the >10 μm size fraction, and increased up to 5-fold in the blooms. The two years differed in the magnitude of the surface chl a increase (2009>2008), the abundance of pennate diatoms within the bloom (2009>2008), and the substantially greater mixed layer depth in 2009. Only the 2009 bloom had sufficient chl a in the >10 μm fraction to produce the observed ocean color chl increase. Blooms had high spatial variability; ocean color images likely average over numerous small events over time and space scales that exceed the individual event scale. Summertime DDA export flux noted at the Hawaii time-series Sta. ALOHA is probably a generalized feature of the eastern N. Pacific north to the subtropical front.     

The carbohydrates of Phaeocystis and their degradation in the microbial food web

The ubiquity and high productivity associated with blooms of colonial Phaeocystis makes it an important contributor to the global carbon cycle. During blooms organic matter that is rich in carbohydrates is produced. We distinguish five different pools of carbohydrates produced by Phaeocystis. Like all plants and algal cells, both solitary and colonial cells produce (1) structural carbohydrates, (hetero) polysaccharides that are mainly part of the cell wall, (2) mono- and oligosaccharides, which are present as intermediates in the synthesis and catabolism of cell components, and (3) intracellular storage glucan. Colonial cells of Phaeocystis excrete (4) mucopolysaccharides, heteropolysaccharides that are the main constituent of the mucous colony matrix and (5) dissolved organic matter (DOM) rich in carbohydrates, which is mainly excreted by colonial cells. In this review the characteristics of these pools are discussed and quantitative data are summarized. During the exponential growth phase, the ratio of carbohydrate-carbon (C) to particulate organic carbon (POC) is approximately 0.1. When nutrients are limited, Phaeocystis blooms reach a stationary growth phase, during which excess energy is stored as carbohydrates. This so-called overflow metabolism increases the ratio of carbohydrate-C to POC to 0.4–0.6 during the stationary phase, leading to an increase in the C/N and C/P ratios of Phaeocystis organic matter. Overflow metabolism can be channeled towards both glucan and mucopolysaccharides. Summarizing the available data reveals that during the stationary phase of a bloom glucan contributes 0–51% to POC, whereas mucopolysaccharides contribute 5–60%. At the end of a bloom, lysis of Phaeocystis cells and deterioration of colonies leads to a massive release of DOM rich in glucan and mucopolysaccharides. Laboratory studies have revealed that this organic matter is potentially readily degradable by heterotrophic bacteria. However, observations in the field of accumulation of DOM and foam indicate that microbial degradation is hampered. The high C/N and C/P ratios of Phaeocystis organic matter may lead to nutrient limitation of microbial degradation, thereby prolonging degradation times. Over time polysaccharides tend to self-assemble into hydrogels. This may have a profound effect on carbon cycling, since hydrogels provide a vehicle to move DOM up the size spectrum to sizes subject to sedimentation. In addition, it changes the physical nature and microscale structure of the organic matter encountered by bacteria which may affect the degradation potential of the Phaeocystis organic matter.     

Dynamics of transparent exopolymeric particles (TEP) production by Phaeocystis globosa under N- or P-limitation: a controlling factor of the retention/export balance

The concentration of transparent exopolymeric particles (TEP) was monitored during Phaeocystis globosa blooms that developed in mesocosms under different initial N:P ratios (from N- to P-limited conditions). TEP concentration was measured using the microscopic (TEP_micro, ppm) and the colorimetric (TEP_color, Xanthan equiv. L⁻¹) methods. TEP concentrations varied from 5 to >75 ppm and from 60 to >1500 μg Xanthan equiv. L⁻¹, and were relatively low until the mesocosms reached nutrient (either N or P) depletion and then increased abruptly. From the TEP_micro versus TEP_color concentrations comparison and from their relation to chlorophyll a concentrations, two phases for the dynamics of TEP production were identified: (1) production through active release of precursors during the growth phase of P. globosa — defined as TEP₁ — and their integration into the TEP pool through coagulation processes; (2) release of large TEP from the mucilaginous matrix of P. globosa colonies subsequent to disruption caused by nutrient depletion — defined as TEP₂ — and their direct integration into the TEP pool outside the constraint of coagulation. The formation of a multiorigin TEP pool during P. globosa blooms may have implications for the fate of the blooms, due to difference in TEP bioreactivity according to their source and to difference in timing and intensity of TEP₁ versus TEP₂ production according to N- or P-depletion. For P. globosa blooms developing under N-limiting conditions, the transition from the first source (i.e. TEP₁) to the second one (i.e. TEP₂) was a slow and continuous process. In contrast, the P. globosa bloom developing under P-limiting conditions showed the sudden formation of heavy mucous aggregates when P became depleted, that may have been caused by a massive release of TEP₂. Our study suggests that the nutrient regime may control the export vs. retention balance during P. globosa blooms, via production of a multiorigin TEP pool.     

Mechanisms of signal transduction in photo-stimulated secretion in Phaeocystis globosa

Phaeocystis globosa, a leading agent in marine carbon cycling, releases its photosynthesized biopolymers via regulated exocytosis. Release is elicited by blue light and relayed by a characteristic cytosolic Ca(2+) signal. However, the source of Ca(2+) in these cells has not been established. The present studies indicate that Phaeocystis' secretory granules work as an intracellular Ca(2+) oscillator. Optical tomography reveals that photo-stimulation induces InsP(3)-triggered periodic lumenal [Ca(2+)] oscillations in the granule and corresponding out-of-phase cytosolic oscillations of [Ca(2+)] that trigger exocytosis. This Ca(2+) dynamics results from an interplay between the intragranular polyanionic matrix, and two Ca(2+)-sensitive ion channels located on the granule membrane: an InsP(3)-receptor-Ca(2+) channel, and an apamin-sensitive K(+) channel.