Mixotrophic Dinoflagellate Research Articles

Turbidity Maximum Entrapment of Phytoplankton in the Chesapeake Bay

Estuarine turbidity maxima (ETM) play an important role in zooplankton and larval fish productivity in many estuaries. Yet in many of these systems, little is known about the food web that supports this secondary production. To see if phytoplankton have the potential to be a component of the ETM food web in the Chesapeake Bay estuary a series of cruises were carried out to determine the biomass distribution and floral composition of phytoplankton in and around the ETM during the winter and spring using fluorometry, high-performance liquid chromatography (HPLC), and microscopy. Two distinct phytoplankton communities were observed along the salinity gradient. In lower salinity waters, biomass was low and the community was composed mostly of diatoms, while in more saline waters biomass was high and the community was composed mostly of mixotrophic dinoflagellates, which were often concentrated in a thin layer below the pycnocline. Phytoplankton biomass was always low in the ETM, but high concentrations of phytoplankton pigment degradation products and cellular remains were often observed suggesting that this was an area of high phytoplankton mortality and/or an area where phytoplankton derived particulate organic matter was being trapped. These results, along with a box model analysis, suggest that under certain hydrodynamic conditions phytoplankton derived organic matter can be trapped in ETM and potentially play a role in fueling secondary production.

Dynamics of late spring and summer phytoplankton communities on Georges Bank, with emphasis on diatoms, Alexandrium spp., and other dinoflagellates

We analyzed the distribution, abundance, and succession patterns of major phytoplankton taxa on Georges Bank in relation to hydrography, nutrients, and size-fractionated chlorophyll concentrations (>20μm; <20μm) on three oceanographic cruises from late spring through summer 2008 (28 April–5 May, 27 May–4 June, and 27 June–3 July). The April–May phytoplankton community was dominated numerically by the diatoms Skeletonema spp., Thalassiosira spp., Coscinodiscus spp., and Chaetoceros spp., with highest total diatom cell densities exceeding 200,000cellsl−1 on the Northeast Peak. In May–June, low nitrate and silicate concentrations over the Bank, along with patches of slightly elevated ammonium, were apparently supporting a predominantly dinoflagellate population; the toxic dinoflagellate Alexandrium spp. reached 13,000cellsl−1. Diatom cell densities on the second cruise in May–June were less than 60,000cellsl−1 and their spatial distributions did not overlap with the highest cell densities of Alexandrium spp. or other dinoflagellates. On the third and last cruise, in June–July, reduced nitrate and silicate concentrations were accompanied by a shift in the phytoplankton community: Alexandrium spp. cell densities were lower and heterotrophic and mixotrophic dinoflagellates, notably Polykrikos spp., Gyrodinium spp., Gymnodinium spp., and Prorocentrum spp., had become more abundant. Patches of regenerated silicate during the June–July period appeared to support a post-spring-bloom diatom community on the central crest of the Bank (total diatom cell densities >180,000cellsl−1) of Leptocylindrus spp., Dactyliosolen spp., and Guinardia flaccida. Multivariate statistical analyses of phytoplankton taxa and station locations revealed distinct assemblages of diatom and dinoflagellate taxa on the Bank throughout the late spring and summer. Results are interpreted in the ecological context of earlier-reported laboratory culture experiments on the competitive interactions between Alexandrium fundyense and diatoms.

Production and excretion of okadaic acid, pectenotoxin-2 and a novel dinophysistoxin from the DSP-causing marine dinoflagellate Dinophysis acuta – Effects of light, food availability and growth phase

Diarrhetic shellfish poisoning (DSP) toxins constitute a severe economic threat to shellfish industries and a major food safety issue for shellfish consumers. The prime producers of the DSP toxins that end up in filter feeding shellfish are species of the marine mixotrophic dinoflagellate genus Dinophysis. Intraspecific toxin contents of Dinophysis spp. vary a lot, but the regulating factors of toxin content are still poorly understood. Dinophysis spp. have been shown to sequester and use chloroplasts from their ciliate prey, and with this rare mode of nutrition, irradiance and food availability could play a key role in the regulation of toxins contents and production. We investigated toxin contents, production and excretion of a Dinophysis acuta culture under different irradiances, food availabilities and growth phases. The newly isolated strain of D. acuta contained okadaic acid (OA), pectenotoxins-2 (PTX-2) and a novel dinophysistoxin (DTX) that we tentatively describe as DTX-1b isomer. We found that all three toxins were excreted to the surrounding seawater, and for OA and DTX-1b as much as 90% could be found in extracellular toxin pools. For PTX-2 somewhat less was excreted, but often >50% was found extracellularly. This was the case both in steady-state exponential growth and in food limited, stationary growth, and we emphasize the need to include extracellular toxins in future studies of DSP toxins. Cellular toxin contents were largely unaffected by irradiance, but toxins accumulated both intra- and extracellularly when starvation reduced growth rates of D. acuta. Toxin production rates were highest during exponential growth, but continued at decreased rates when cell division ceased, indicating that toxin production is not directly associated with ingestion of prey. Finally, we explore the potential of these new discoveries to shed light on the ecological role of DSP toxins.

Effects of light and food availability on toxin production, growth and photosynthesis in Dinophysis acuminata

Diarrhetic shellfish poisoning (DSP) toxins constitute a severe health risk to shellfish consumers and a serious economic risk to the shellfish industry. The most prominent producers of DSP toxins are the mixotrophic dinoflagellates Dinophysis spp., which rely on chloroplasts from their prey, the ciliate Mesodinium rubrum; i.e. they are kleptoplastidic. Studies based on field col- lected material have indicated that cellular toxin contents in Dinophysis spp. vary intraspecifically by several orders of magnitude, but the regulating factors of cellular toxin contents are still poorly understood. We isolated 7 strains of D. acuminata, all of which produced pectenotoxin-2 (PTX-2) in the range of 12.7 to 35.6 pg cell �1 when supplied with abundant nutrients, light and food. One strain was selected for detailed studies on the effects of irradiance and food availability on pho- toacclimation, photosynthesis, growth and toxin production. Photoacclimation was detected for the first time in this genus, indicating some genetic control of sequestered chloroplasts. Growth and photosynthesis increased 4-fold with irradiances from 7 to 130 µmol photons m �2 s �1 after a minimum of 2 wk under ample food conditions. Despite this, cellular PTX-2 content increased only slightly from (mean ±SE) 4.6 ± 0.3 to 7.8 ± 1.1 pg PTX-2 cell �1 . Toxin production continued for up to 30 d after food was depleted, leading to a build-up of toxin in D. acuminata cells to 24.7 ± 1.7 pg PTX-2 cell �1 . Thus, we demonstrate that PTX-2 content is not directly coupled to irradiance and that PTX-2 production is not directly associated with ingestion of ciliate prey. Intraspecific varia- tions in toxicity are instead most likely governed primarily by growth phase and genetic differ- ences between different populations of Dinophysis spp.

On the roles of cell size and trophic strategy in North Atlantic diatom and dinoflagellate communities

We have examined the inter‐ and intra‐group seasonal succession of 113 diatom and dinoflagellate taxa, as surveyed by the Continuous Plankton Recorder (CPR) in the North Atlantic, by grouping taxa according to two key functional traits: cell size (µg C cell−1) and trophic strategy (photoautotrophy, mixotrophy, or heterotrophy). Mixotrophic dinoflagellates follow photoautotrophic diatoms but precede their obligate heterotrophic counterparts in the succession because of the relative advantages afforded by photosynthesizing when light and nutrients are available in spring. The mean cell size of the sampled diatoms is smallest in the summer, likely because of the higher specific nutrient affinity of smaller relative to larger cells. Contrastingly, we hypothesize that mixotrophy diminishes the size selection based on nutrient limitation and accounts for the lack of a seasonal size shift among surveyed dinoflagellates. Relatively small, heterotrophic dinoflagellates (µg C cell−1 &lt; 10−3) peak after other, larger dinoflagellates, in part because of the increased abundance of their small prey during nutrient‐deplete summer months. The largest surveyed diatoms (µg C cell−1 &gt; 10−2) bloom later than others, and we hypothesize that this may be because of their relatively slow maximum potential growth rates and high internal nutrient storage, as well as to the slower predation of these larger cells. The new trait database and analysis presented here helps translate the taxonomic information of the CPR survey into metrics that can be directly compared with trait‐based models.

Influence of inorganic nutrients, irradiance, and time of day on food uptake by the mixotrophic dinoflagellate Neoceratium furca

While phagotrophy is reported for a number of phytoflagellates, the factors that influ- ence feeding are known for only a few species. We examined the effects of nutrients, irradiance, and time of day on ingestion rate by field populations of the mixotrophic dinoflagellate Neocera - tium furca. In nutrient addition assays, N. furca consistently showed a significant reduction in feeding when inorganic nitrogen (N) and phosphorus (P) were added together. Responses to sep- arate N or P addition varied, with ingestion rates decreasing, increasing, or remaining unaltered depending on which nutrient was potentially limiting, as indicated by inorganic nutrient concen- trations. Feeding was also influenced by light and was often highest at or below irradiance levels comparable to those experienced by cells at time of collection. Darkness and/or high irradiance sometimes led to a decrease in feeding, possibly due to reduced nutrient demand or photoinhibi- tion. Ingestion rates of N. furca over the course of a day showed distinct but conflicting diel feed- ing patterns. While feeding increased during the day in one experiment, ingestion rates were higher at night in the other. These patterns were likely a direct response to the changing light environment over the course of the day, as they agreed well with findings for the same N. furca populations during the corresponding light level experiments. Results from both nutrient addition and light level experiments confirm that N. furca employed phagotrophy primarily as an alterna- tive means of obtaining limiting nutrients rather than carbon.

Temporal dynamics of carbon flow through the microbial plankton community in a coastal upwelling system off northern Baja California, Mexico

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 461:31-46 (2012) - DOI: https://doi.org/10.3354/meps09782 Temporal dynamics of carbon flow through the microbial plankton community in a coastal upwelling system off northern Baja California, Mexico Lorena Linacre1, 2,*, Michael R. Landry3, Ramón Cajal-Medrano4, J. Rubén Lara-Lara5, J. Martín Hernández-Ayón6, Rosa R. Mouriño-Pérez2, Ernesto García-Mendoza5, Carmen Bazán-Guzmán5 1Programa de Doctorado en Oceanografía Costera, Facultad de Ciencias Marinas/Instituto de Investigaciones Oceanológicas, 4Facultad de Ciencias Marinas, and 6Instituto de Investigaciones Oceanológicas; Universidad Autónoma de Baja California (UABC), Ensenada, Baja California 22860, Mexico 2Departamento de Microbiología, División de Biología Experimental y Aplicada, and 5Departamento de Oceanografía Biológica, División de Oceanología; Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Ensenada, Baja California 22860, Mexico 3Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093-0227, USA *Email: lorenalinacre@gmail.com ABSTRACT: We investigated the temporal dynamics of carbon flow through the microbial food web of a coastal upwelling system (ENSENADA station) off northern Baja California during 6 cruises (September 2007 to November 2008). Carbon biomass assessments for major autotrophic size groups (pico- to micro-sized cells) and their microzooplankton grazers were based on analyses using flow cytometry, HPLC pigments and epifluorescence microscopy. Taxon-specific phytoplankton growth and microzooplankton grazing rates were determined from 24 h in situ incubations in the euphotic zone using an abbreviated 3-treatment dilution technique. Carbon biomass and instantaneous growth and grazing rate determinations were used to estimate daily rates of taxon-specific production and losses due to microzooplankton grazing. Overall, microbial biomass showed a close balance between autotrophic and heterotrophic components, except during a period of very strong upwelling (April 2008), which favored large phytoplankters and high primary production. Throughout a wide range of environmental conditions, the community primary production (PP) attributed both to small (mostly picophytoplankton and prasinophytes) and large (mostly diatoms and autotrophic dinoflagellates) autotrophs was significantly grazed (78 ± 9% of PP) by small (<20 µm) and large (>20 µm) ciliates and flagellates (including mixotrophic dinoflagellates), respectively, showing complementary temporal shifts in protistan grazer types that matched the dominant phytoplankton. While large diatoms were strongly consumed by large ciliates during the 2 most productive periods (September 2007 and April 2008), pico- and nano-sized phytoplankton were grazed most by nanoflagellates and small ciliates from November 2007 to January 2008. Consequently, biogenic carbon production in this ecosystem is transferred through a multivorous food web. KEY WORDS: Biogenic carbon flow · Multivorous food web · Phytoplankton growth rate · Phytoplankton grazing rate · Primary production Full text in pdf format PreviousNextCite this article as: Linacre L, Landry MR, Cajal-Medrano R, Lara-Lara JR and others (2012) Temporal dynamics of carbon flow through the microbial plankton community in a coastal upwelling system off northern Baja California, Mexico. Mar Ecol Prog Ser 461:31-46. https://doi.org/10.3354/meps09782 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 461. Online publication date: August 08, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Marine microalgae attack and feed on metazoans

Free-living microalgae from the dinoflagellate genus Karlodinium are known to form massive blooms in eutrophic coastal waters worldwide and are often associated with fish kills. Natural bloom populations, recently shown to consist of the two mixotrophic and toxic species Karlodinium armiger and Karlodinium veneficum have caused fast paralysis and mortality of finfish and copepods in the laboratory, and have been associated with reduced metazooplankton biomass in-situ. Here we show that a strain of K. armiger (K-0688) immobilises the common marine copepod Acartia tonsa in a density-dependent manner and collectively ingests the grazer to promote its own growth rate. In contrast, four strains of K. veneficum did not attack or affect the motility and survival of the copepods. Copepod immobilisation by the K. armiger strain was fast (within 15 min) and caused by attacks of swarming cells, likely through the transfer and action of a highly potent but uncharacterised neurotoxin. The copepods grazed and reproduced on a diet of K. armiger at densities below 1000, cells ml(-1), but above 3500 cells ml(-1) the mixotrophic dinoflagellates immobilised, fed on and killed the copepods. Switching the trophic role of the microalgae from prey to predator of copepods couples population growth to reduced grazing pressure, promoting the persistence of blooms at high densities. K. armiger also fed on three other metazoan organisms offered, suggesting that active predation by mixotrophic dinoflagellates may be directly involved in causing mortalities at several trophic levels in the marine food web.

Toxic mucus traps: A novel mechanism that mediates prey uptake in the mixotrophic dinoflagellate Alexandrium pseudogonyaulax

The functional role of harmful substances (i.e. toxins) produced by marine planktonic algae is still, in many cases, unknown. This study describes a novel mechanism by which the phototrophic dinoflagellate Alexandrium pseudogonyaulax secretes a toxic mucus trap where prey items are caught and immobilized prior to ingestion. Prey cells remain entrapped and immobile in the mucus trap, but most stay intact, readily available as whole-cell prey. It is shown that food uptake by A. pseudogonyaulax increases its growth rate considerably even in nutrient-replete, high-light conditions. The increase in growth rate was more enhanced in light-limited treatments and A. pseudogonyaulax grew significantly faster when fed Heterocapsa rotundata, than when fed Teleaulax acuta under both light conditions. For comparison, strains of Alexandrium catenella and Alexandrium minutum were studied for their mixotrophic capabilities. None of these strains were mixotrophic under the conditions provided. In addition, the toxic effects on various protistan targets of these Alexandrium strains as well as Alexandrium tamarense and Alexandrium ostenfeldii were compared to that of A. pseudogonyaulax. A. tamarense and A. catenella did immobilize and lyse target cells through substances leaked directly into the water, differing from all the strains of A. pseudogonyaulax studied. Results show that the toxic effect of A. pseudogonyaulax is non-specific causing nearly 100% immobilization of a variety of protistan targets at relatively low cell concentrations (500cellsml−1 of donor cell). A critical donor cell density was not required as only one A. pseudogonyaulax cell was able to cause immobilization of target cells. For the first time, the connection between excreted toxins and phagotrophy is evident in an Alexandrium species and this particular strategy has the potential to severely impact competing phytoplankton communities.

Community metabolism and energy transfer in the Chesapeake Bay estuarine turbidity maximum

In an effort to identify the key mechanisms controlling biological productivity and food web structure in the Chesapeake Bay estuarine turbidity maxima (ETM), we measured plankton community metabolism on a series of surveys in the upper Chesapeake Bay during the winter and spring of 2007 and 2008. Measured quantities included primary production, bacterial production, planktonic community respiration, and algal pigment concentrations. These measurements revealed a classic minimum in photosynthesis in the vicinity of the ETM. Temporal variability in plankton community metabolism, primary production, respiration, and bacterial production, were highest in the southern oligohaline region down-estuary of the ETM, and appeared to be driven by dynamic bio-physical interactions. Elevated primary production and community respiration in this region were often associated with the presence of mixotrophic dinoflagellates. The dinoflagellate contribution to primary production and respiration appeared to be particularly large as a result of their mixotrophic capabilities, which allow them to obtain energy both autotrophically and heterotrophically. This study suggests that mixotrophic dinoflagellates play a key role in pelagic food web in the oligohaline region of Chesapeake Bay supplying most of the labile organic matter during late winter and spring and also providing a vector for transferring microbial production to mesozooplankton.

Mixotrophic and heterotrophic dinoflagellates in eutrophic coastal waters of the Aegean Sea (eastern Mediterranean Sea)

Abstract In the period 2001–2003, I quantitatively explored the importance of mixotrophic and heterotrophic dinoflagellates in four eutrophic gulfs on the Greek coastline of the Aegean Sea, eastern Mediterranean. Phytoplankton analysis (250 samples, 401 species) focused on determinations of cell abundance and carbon biomass of diatoms, dinoflagellates (autotrophic, mixotrophic, heterotrophic), and coccolithophores. Among the 177 dinoflagellates, 145 autotrophic, 18 mixotrophic, and 14 heterotrophic species were identified comprising up to 18%, 3%, and 1% of total phytoplankton cell abundance, respectively. Analysis of total carbon biomass contributions among taxa showed that the heterotrophic dinoflagellate population contributed the highest carbon proportion (65%) to the stocks of phytoplankton community in contrast to the low contributions of the autotrophic (14%) and mixotrophic (1%) dinoflagellate species. One heterotrophic and 11 mixotrophic species were harmful algae. This major contribution of heterotrophic species to total carbon biomass may affect the concepts of trophodynamics and food web structure. Seasonal and regional distributions of heterotrophic and mixotrophic dinoflagellates are considered.

Changes in phytoplankton composition in response to tides, wind-induced mixing conditions, and freshwater outflows in an urbanised estuarine complex

Recent reports have shown an increase in potentially harmful phytoplankton in Santos bay (Southeastern Brazilian Coast), located in a highly urbanised estuarine complex. Prediction of blooms is, thus, essential but the phytoplankton community structure in very dynamic regions is difficult to determine. In the present work, we discriminate bloom forming microphytoplankton dominance and their relationship to physical and meteorological variables to look for patterns observed in different tides and seasons. Comparing 8 distinct situations, we found five scenarios of dominance that could be related to winds, tides and rainfall: i) Surfers, diatoms occurring during high surf zone energies; ii) Sinkers, represented by larger celled diatoms during spring tide, after periods of high precipitation rates; iii) Opportunistic mixers, composed of chain forming diatoms with small or elongate cells occurring during neap tides; iv) Local mixers, microplanktonic diatoms and dinoflagellates which occurred throughout the 298 sampling stations; and v) Mixotrophic dinoflagellates, after intense estuarine discharges. Results suggest alterations in the temporal patterns for some bloom-forming species, while others appeared in abundances above safe limits for public health. This approach can also illustrate possible impacts of changes in freshwater discharge in highly urbanised estuaries.

Feeding on copepod fecal pellets: a new trophic role of dinoflagellates as detritivores

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 441:65-78 (2011) - DOI: https://doi.org/10.3354/meps09357 Feeding on copepod fecal pellets: a new trophic role of dinoflagellates as detritivores Louise K. Poulsen1,*, Morten Moldrup2, Terje Berge3, Per Juel Hansen2 1Technical University of Denmark, Charlottenlund Castle, Jægersborg Allé 1, 2920 Charlottenlund, Denmark 2Marine Biological Section, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark 3Marine Biological Section, University of Copenhagen, Østre Farimagsgade 2D, 1353 Copenhagen K, Denmark *Email: lkp@aqua.dtu.dk ABSTRACT: Recent field studies indicate that dinoflagellates are key degraders of copepod fecal pellets. This study is the first to publish direct evidence of pellet grazing by dinoflagellates. Feeding and growth on copepod fecal pellets were studied for both heterotrophic (4 species) and mixotrophic dinoflagellates (3 species) using a combination of classic incubation experiments and video recordings of feeding behavior. Fecal pellets were produced by adult Acartia tonsa feeding on Rhodomonas salina. Two mixotrophic species (Karlodinium armiger, a gymnodinoid dinoflagellate, Gy1) and all heterotrophic dinoflagellates (Gyrodinium dominans, Gyrodinium spirale, Diplopsalis lenticula, Protoperidinium depressum) studied fed on fecal pellets. Using natural concentrations of dinoflagellates and copepod fecal pellets, average ingestion rates of 0.2 and 0.1 pellets cell−1 d−1 and clearance rates of between 0.2 and 0.3 ml cell−1 d−1 were obtained for G. spirale and P. depressum, respectively. Pellet feeding resulted in average growth rates of 0.69 and 0.08 d−1 with growth yields of 0.58 and 0.50 for G. spirale and P. depressum. Important factors for the grazing impact of the dinoflagellates on fecal pellets in this study were: dinoflagellate concentration, the dinoflagellate-to-pellet size ratio, the feeding mechanism, pellet food source, and pellet age. This study reveals a new trophic role for dinoflagellates as detritivores, and shows that large (>20 µm) heterotrophic dinoflagellates alone can account for reported pellet degradation rates in field studies. Thus, dinoflagellates can function as an effective ‘protozoan filter’ for fecal pellets in the water column. KEY WORDS: Detritivorous feeding · Fecal pellet degradation · Fecal pellet grazing · Detection distance · Microzooplankton · Chemosensory response · Avoidance Full text in pdf format PreviousNextCite this article as: Poulsen LK, Moldrup M, Berge T, Hansen PJ (2011) Feeding on copepod fecal pellets: a new trophic role of dinoflagellates as detritivores. Mar Ecol Prog Ser 441:65-78. https://doi.org/10.3354/meps09357 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 441. Online publication date: November 15, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Prey‐dependent retention of dimethylsulfoniopropionate (DMSP) by mixotrophic dinoflagellates

SummaryWe investigated the retention of dimethylsulfoniopropionate (DMSP) in phototrophic dinoflagellates arising from mixotrophy by estimating the cellular content of DMSP in Karlodinium veneficum (mixotrophic growth) fed for 7–10 days on either DMSP-rich Amphidinium carterae (phototrophic growth only) or DMSP-poor Teleaulax sp. (phototrophic growth only). In K. veneficum fed on DMSP-poor prey, the cellular content of DMSP remained almost unchanged regardless of the rate of feeding, whereas the cellular content of DMSP in cells of K. veneficum fed on DMSP-rich prey increased by as much as 21 times the cellular concentration derived exclusively from phototrophic growth. In both cases, significant fractions (10–32% in the former case and 55–65% in the latter) of the total DMSP ingested by K. veneficum were transformed into dimethylsulfide and other biochemical compounds. The results may indicate that the DMSP content of prey species affects temporal variations in the cellular DMSP content of mixotrophic dinoflagellates, and that mixotrophic dinoflagellates produce DMS through grazing on DMSP-rich preys. Additional studies should be performed to examine the universality of our finding in other mixotrophic dinoflagellates feeding on diverse prey species.

Comparative proteomics of the mixotrophic dinoflagellate Prorocentrum micans growing in different trophic modes

Protein profiles of a common mixotrophic dinoflagellate, Prorocentrum micans, growing autotrophically and mixotrophically (fed on the cryptophyte Rhodomonas salina) were compared using two-dimensional gel electrophoresis (2DE) to determine if they vary in different trophic modes. Approximately 2.3% of the detected proteins were differentially expressed in the different trophic modes. Twelve proteins observed only in the mixotrophic condition had lower pI value ( 5). When the internal amino acid sequences of five selected proteins differentially expressed between autotrophic and mixotrophic conditions were analyzed us ing matrix-assisted laser desorption time-of-flight (MALDI-TOF) mass spectrometry, two proteins that were specifically expressed in the autotrophic condition showed homology to glyceraldehyde-3-phosphatase dehydrogenase (GAPDH) and a bacterial catalase. Three mixotrophy-specific proteins showed homology to certain hypothetical proteins from an insect and bacteria. These results suggested the presence of certain gene groups that are switched on and off according to the trophic mode of P. micans.

Feeding behavior, spatial distribution and phylogenetic affinities of the heterotrophic dinoflagellate Oxyphysis oxytoxoides

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 62:279-287 (2011) - DOI: https://doi.org/10.3354/ame01474 Feeding behavior, spatial distribution and phylogenetic affinities of the heterotrophic dinoflagellate Oxyphysis oxytoxoides Myung Gil Park1, Hwayoung Lee1, Kwang Young Kim1, Sunju Kim2,* 1Department of Oceanography, Chonnam National University, Gwangju 500-757, Republic of Korea 2Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, Maryland 21037, USA *Corresponding author. Email: sunjukim75@gmail.com ABSTRACT: We documented the abundance of the heterotrophic dinoflagellate Oxyphysis oxytoxoides Kofoid along the Korean coast, cultured it (food source: the marine ciliate Myrionecta rubra Jankowski [= Mesodinium rubrum Lohmann]), sequenced its nuclear-encoded large-subunit (LSU) rDNA, and resolved its phylogenetic relationship within the Dinophysiales. Abundance was low, usually <9.7 × 103 cells l–1, in samples from 2005 and 2006. It co-occurred with the mixotrophic dinoflagellate Dinophysis acuminata, possibly indicating a common pool of prey. Growth on M. rubra reached a density of 38 × 105 cells l–1. Observations on live cells from our established cultures revealed that O. oxytoxoides uses a peduncle to suck up the cell contents of M. rubra, the number of food vacuoles increasing as feeding proceeds. No regional variability was found in partial LSU rDNA sequences (domains D1–D2) of our strains, despite different sampling sites and dates. Phylogenetic analysis, based on LSU rDNA, showed that while Amphisolenia forms an early divergent basal group in the Dinophysiales, the other dinophysoids form 2 separate groups: (1) Oxyphysis and Phalacroma, and (2) Histioneis, Ornithocercus, Citharistes and Dinophysis. The presence of a peduncle in several genera, and the widespread distribution of pedunculate dinophysoids, indicate that these species may be fundamentally heterotrophic with a common feeding mechanism. Our results shed light on the feeding ecology and phylogenetic position of O. oxytoxoides. KEY WORDS: Dinophysiales · Myrionecta rubra · Oxyphysis oxytoxoides · Peduncle feeding · Phylogeny Full text in pdf format Supplementary material PreviousNextCite this article as: Park MG, Lee H, Kim KY, Kim S (2011) Feeding behavior, spatial distribution and phylogenetic affinities of the heterotrophic dinoflagellate Oxyphysis oxytoxoides. Aquat Microb Ecol 62:279-287. https://doi.org/10.3354/ame01474 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 62, No. 3. Online publication date: February 08, 2011 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2011 Inter-Research.

Dinoflagellates and ciliates at Helgoland Roads, North Sea

A monitoring programme for microzooplankton was started at the long-term sampling station “Kabeltonne” at Helgoland Roads (54°11.3′N; 7°54.0′E) in January 2007 in order to provide more detailed knowledge on microzooplankton occurrence, composition and seasonality patterns at this site and to complement the existing plankton data series. Ciliate and dinoflagellate cell concentration and carbon biomass were recorded on a weekly basis. Heterotrophic dinoflagellates were considerably more important in terms of biomass than ciliates, especially during the summer months. However, in early spring, ciliates were the major group of microzooplankton grazers as they responded more quickly to phytoplankton food availability. Mixotrophic dinoflagellates played a secondary role in terms of biomass when compared to heterotrophic species; nevertheless, they made up an intense late summer bloom in 2007. The photosynthetic ciliate Myrionecta rubra bloomed at the end of the sampling period. Due to its high biomass when compared to crustacean plankton especially during the spring bloom, microzooplankton should be regarded as the more important phytoplankton grazer group at Helgoland Roads. Based on these results, analyses of biotic and abiotic factors driving microzooplankton composition and abundance are necessary for a full understanding of this important component of the plankton.

Transformation of iodate to iodide in marine phytoplankton driven by cell senescence

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 11:1-15 (2010) - DOI: https://doi.org/10.3354/ab00284 FEATURE ARTICLE Transformation of iodate to iodide in marine phytoplankton driven by cell senescence K. Bluhm1,*, P. Croot1, K. Wuttig1, K. Lochte2 1IFM-GEOMAR, Leibniz Institute for Marine Sciences, Marine Biogeochemistry, Westshore Building, Duesternbrooker Weg 20, 24105 Kiel, Germany 2Alfred-Wegener-Institute for Polar- and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany *Email: kbluhm@ifm-geomar.de ABSTRACT: Previous studies have suggested that phytoplankton play an important role in the biogeochemical cycling of iodine, due to the appearance of iodide in the euphotic zone. Changes in the speciation of iodine over the course of the growth cycle were examined in culture media for a variety of phytoplankton taxa (diatoms, dinoflagellates and prymnesiophytes). All species tested showed the apparent ability to reduce iodate to iodide, though production rates varied considerably between species (0.01 to 0.26 nmol l–1 µg–1 chl a d–1), with Eucampia antarctica the least and Pseudo-nitzschia turgiduloides the most efficient iodide producers. Production was found to be species specific and was not related to biomass (indicated by e.g. cell size, cell volume, or chl a content). In all species, except for the mixotrophic dinoflagellate Scrippsiella trochoidea, iodide production commenced in the stationary growth phase and peaked in the senescent phase of the algae, indicating that iodide production is connected to cell senescence. This suggests that iodate reduction results from increased cell permeability, which we hypothesize is due to subsequent reactions of iodate with reduced sulphur species exuded from the cell. A shift from senescence back to the exponential growth phase resulted in a decline in iodide and indicated that phytoplankton-mediated oxidation of iodide to iodate was likely to be occurring. Iodide production could not be observed in healthy cells kept in the dark for short periods. Bacterial processes appeared to play only a minor role in the reduction of iodate to iodide. KEY WORDS: Iodine speciation · Iodide · Iodate · Antarctic diatoms · Nitrate reductase · Glutathione · Sulphur species · Cell senescence Full text in pdf format Information about this Feature Article NextCite this article as: Bluhm K, Croot P, Wuttig K, Lochte K (2010) Transformation of iodate to iodide in marine phytoplankton driven by cell senescence. Aquat Biol 11:1-15. https://doi.org/10.3354/ab00284 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 11, No. 1. Online publication date: October 28, 2010 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2010 Inter-Research.

PREY SPECIFICITY AND FEEDING OF THE THECATE MIXOTROPHIC DINOFLAGELLATE FRAGILIDIUM DUPLOCAMPANAEFORME1

In summer to autumn of 2008, a recently described thecate mixotrophic dinoflagellate, Fragilidium duplocampanaeforme Nézan et Chomérat, occurred in Masan Bay, Korea, where it frequently contained bright‐orange fluorescent inclusions. Using cultures of F. duplocampanaeforme isolated from Masan Bay, we investigated feeding, digestion, and prey specificity of this mixotroph. F. duplocampanaeforme fed exclusively on Dinophysis spp. when offered a variety of prey including dinoflagellates, a raphidophyte, a cryptophyte, a ciliate, and diatoms separately. In addition, F. duplocampanaeforme had allelopathic effects on other organisms, including cell immobilization/motility decrease (in Dinophysis acuminata, D. caudata, D. fortii, D. infundibulus, Gonyaulax polygramma, Heterocapsa triquetra, and Prorocentrum triestinum), breaking of cell chains (in Cochlodinium polykrikoides), cell death (in Prorocentrum minimum), and temporary cyst formation (in Scrippsiella trochoidea). F. duplocampanaeforme engulfed whole Dinophysis cells through the sulcus. About 1 h after ingestion, F. duplocampanaeforme became immobile and shed all thecal plates. The ecdysal cyst persisted for ∼7 h, during which the ingested prey was gradually digested. These observations suggest that F. duplocampanaeforme may play an important role in the Dinophysis population dynamics in the field.

Feeding by the Newly Described Mixotrophic Dinoflagellate Paragymnodinium shiwhaense: Feeding Mechanism, Prey Species, and Effect of Prey Concentration

To investigate the feeding by the newly described mixotrophic dinoflagellate Paragymnodinium shiwhaense (GenBank accession number=AM408889), we explored the feeding process and the kinds of prey species that P. shiwhaense is able to feed on using several different types of microscopes, including a transmission electron microscope and high-resolution video-microscopy. In addition, we measured the growth and ingestion rates of P. shiwhaense on its optimal algal prey Amphidinium carterae as a function of prey concentration. We also measured these parameters for edible prey at a single concentration at which the growth and ingestion rates of P. shiwhaense on A. carterae were saturated. Paragymnodinium shiwhaense feed on algal prey using a peduncle after anchoring the prey by a tow filament. Among the algal prey offered, P. shiwhaense ingested small algal species that had equivalent spherical diameters (ESDs) < or =11 microm (e.g. the prymnesiophyte Isochrysis galbana, the cryptophytes Teleaulax sp. and Rhodomonas salina, the raphidophyte Heterosigma akashiwo, and the dinoflagellates Heterocapsa rotundata and A. carterae). However, it did not feed on larger algal species that had ESDs > or =12 microm (e.g. the dinoflagellates Prorocentrum minimum, Heterocapsa triquetra, Scrippsiella trochoidea, Alexandrium tamarense, Prorocentrum micans, Gymnodinium catenatum, Akashiwo sanguinea, and Lingulodinium polyedrum) or the small diatom Skeletonema costatum. The specific growth rates for P. shiwhaense feeding upon A. carterae increased rapidly with increasing mean prey concentration before saturating at concentrations of ca. 350 ng C/ml (5,000 cells/ml). The maximum specific growth rate (i.e. mixotrophic growth) of P. shiwhaense on A. carterae was 1.097/d at 20 degrees C under a 14:10 h light-dark cycle of 20 microE/m(2)/s, while its growth rate (i.e. phototrophic growth) under the same light conditions without added prey was -0.224/d. The maximum ingestion and clearance rates of P. shiwhaense on A. carterae were 0.38 ng C/grazer/d (5.4 cells/grazer/d) and 0.7 microl/grazer/h, respectively. The calculated grazing coefficients for P. shiwhaense on co-occurring Amphidinium spp. was up to 0.07/h (i.e. 6.7% of the population of Amphidinium spp. was removed by P. shiwhaense populations in 1 h). The results of the present study suggest that P. shiwhaense can have a considerable grazing impact on algal populations.