Flagellate Community Research Articles

Some Heterotrophic Flagellates from a Cultivated Garden Soil in Australia

Summary The flagellates of an Australian garden soil were studied by placing coverslips on wet soil and subsequently examining the coverslips by light microscopy. A number of genera and species were found which have not previously been reported from soil samples. Besides the three new species, Apusomonas australiensis sp. nov., Peltomonas hanelisp. nov., and Sciviamonas terricola gen. nov. sp. nov. they include species from the genera Amastigomonas, Cryptaulax, Paraphysomonas, and Protaspis. Among genera which have been reported from soils, we recorded a number of species previously unreported from soils: Petalomonas pusilla, Bicosoeca epiphytica, Bicosoeca mignotii, and Ancyromonas sigmoides. In addition, we extracted a number of forms which have been found in soil but which are usually not considered as members of the soil flagellate community. They are: Codosiga botrytis, Salpingoeca amphoridium, and Goniomonas truncata. Only a minority of the taxa recorded are thought of as common and widespread in soils, they include: Apusomonas proboscidea, and species of Cercomonas and Spumella. At least part of the difference between communities of flagellates from freshwaters and those of soils are due to different sampling methods and not only to the existence of different communities.

Seasonal variation in bacterial and flagellate communities of deep-sea sediments in a monsoonal upwelling system

We investigated bacterial and nanoflagellate densities in the bottom sediments and overstanding water, during both upwelling and non-upwelling seasons, along transects (depths 704350 m) in the Arabian Sea. Flagellate bacterivory was studied in bottom-water samples. There was a significant decrease with depth in benthic bacteria and benthic nanoflagellates, but except for the shallowest station, not in water column bacteria or flagellates. There were two significant differences between the seasons: bacterial density, biomass and cell volume were significantly larger in the bottom water during the upwelling season, whereas benthic flagellates were significantly more numerous in the sediments in the non upwelling season. Grazing rates were low, but bacterivory had significantly greater impact on bacterial standing in the bottom water during the non-upwelling season.

Heterotrophic flagellates from coastal marine and hypersaline sediments in Western Australia

Summary The communities of heterotrophic flagellates from four sites of differing salinity (from marine to saturated brine) from the Shark Bay region in Western Australia were examined. A total of 46 species were identified, seven of which are described for the first time. New names are Ancyromonas melba n. sp. Bodo cygnus n. sp., Colpodella unguis n. sp., Glissandra innuerende n. gen. n. sp., Pleurostomum turgidum n. sp., Ploeotia azurina n. sp., Rhynchobodo simius n. sp. and Palustrimonas n. gen. The majority of the new species were from hypersaline sites. There was a degree of overlap in the communities present at the different sites, especially between the three lowest salinity sites. Some species, such as Rhynchomonas nasuta, Bodo saltans and B. designis , have been found over a wide range of salinities. There was little evidence for any endemism in the marine site, with all species observed having been recorded previously from at least one other location geographically remote from Shark Bay.

Effects of increased concentration of nitrate and phosphate during a springbloom experiment in mesocosm

A mesocosm experiment was carried out in the early spring of 1991 (19 February to 20 March) in Raunefjorden, Norway. The experiment consisted of four enclosures of which two were initially supplied with nitrate and phosphate corresponding to an increase in concentration of 6 and 0.2 μM, respectively. Effects of an increased concentration of nitrate and phosphate on the development of the annual phytoplankton springbloom was investigated. Measurement of light, temperature, salinity, nutrients, chlorophyll (chl) a, primary production, phytoplankton enumeration and identification were performed daily or every other day. Average daily irradiance during the experiment was low (4.8 mol · m −2 · d −1). Maximum concentrations of biomass (chl a) and primary production were 11.5 μg chl a · 1 −1 and 109 μg C ·1 −1 · d −1. The initial phytoplankton community in all enclosures were dominated by diatoms, mainly Skeletonema costatum (Grev.) Cleve, and maximum cell number of this species was 11.2 · 10 6 1 −1. After 1 wk, the diatoms were replaced by flagellates, due to silicate deficiency (< 2 μM). The fertilized enclosures were dominated by the haptophyte Phaeocystis cf. pouchetii (18 · 10 6 cells 1 −1), and the non-fertilized enclosures were dominated by unidentified flagellates, together with cryptophytes and prasinophytes. High abundance of choanoflagellates and microzooplankton were also registered in the fertilized enclosures (3.3 · 10 6 1 −1 and 11 · 10 6 1 −1, respectively). This indicates that the microzooplankton may have controlled the growth of flagellates by grazing in the fertilized enclosures. The effect of an increased concentration of nitrate and phosphate was not an increase in biomass (chl a) or primary production, but a change in the species composition. The species composition changed from a diatom community dominated by S. costatum to a flagellate community dominated by P. cf. pouchetii. These results also suggest that major limiting factors for the biomass and primary production have been silicate deficiency, low irradiance and temperature.

Significance of the Virus‐Rich 2–200 nm Size Fraction of Seawater for Heterotrophic Flagellates: I. Impact on Growth

Abstract. The effect of artificially changing the concentration of naturally occurring free virus‐like particles (VLPs) on growth of marine heterotrophic flagellates was tested in batch cultures using ultrafiltration technology. This manipulation influenced the course of flagellate growth markedly. During 1 week of incubation the growth of 4 tested flagellate strains (Oxyrrhis marina, Paraphysomonas imperforata, Petalomonas cantuscygni, Pteridomonas danica) was strongly favoured after increasing the VLP concentration. Bacteria, however, were repressed in these treatments beyond 50 h. In cultures with natural seawater microbiota, we both reduced and enriched the concentration of VLPs. In these cultures, reduction of material in the virus‐rich 2–200 nm size fraction led to a strong positive growth response of heterotrophic flagellates. In VLP‐enriched treatments of natural seawater microbiota a tendency toward growth stimulation was also found, although this was not significant. Enrichment with VLPs caused no recognizable mortality either in cultured flagellate strains or in naturally occurring flagellate communities. However, it is suggested that a highly bioactive component must be present in the virus‐rich 2–200 nm size fraction. Virus‐like particles are discussed as possible candidates influencing heterotrophic flagellate community successions.

Channeling of bacterioplanktonic production toward phagotrophic flagellates and ciliates under different seasonal conditions in a river

The objective of this study was to analyze the flux of biomass through the communities of bacteria and phagotrophic protists in the cold and warm conditions occurring seasonally in Butrón River. Bacterial and heterotrophic protistan (flagellate and ciliate) abundance was determined by epifluorescence direct counts; protistan grazing on planktonic bacteria was measured from fluorescently labeled bacteria uptake rates; and the estimate of bacterial secondary production was obtained from [(3)H]thymidine incorporation rates. The abundance of bacterial, flagellate, and ciliate communities was similar during cold and warm situations. However, we observed that estimates of dynamic parameters, i.e., secondary bacterial production and protistan grazing, in both situations were noticeably different. In the warm situation, grazing rates of flagellates and ciliates (bacteria per protist per hour) were, respectively, 7 times and 18 times higher than those determined in the cold situation, and the grazing rates of the protistan communities (bacteria per protists present in 1 ml of water per hour) increased up to 5 times in the case of flagellates and 42 times in the case of ciliates. Estimates of bacterial secondary production were also higher during the warm situation, showing a ninefold increase. The percentage of bacterial production preyed upon by flagellates or ciliates was not significantly different between the two conditions. These results showed that in the different conditions of a system, the flux of biomass between the trophic levels may be quite different although this process may not be reflected in the abundance of each community of bacteria, flagellates, and ciliates.

On the seasonal occurrence of autotrophic naked nanoflagellates in Kiel Bight, western Baltic

From April to October 1986 the occurrence of autotrophic, mainly naked nanoflagellates was surveyed qualitatively and semi-quantitatively at four stations in Kiel Bight and Kiel Fjord by use of the Dilution Culture technique and light-microscopy of live preparations. In April, the flagellate community was characterized by species mostly >10μm ( Cryptomonas pseudobaltica, Katodinium rotundatum, Pseudopedinella pyriforme, Heterosigma akashiwo). After a bloom of Dictyocha speculum in May, mainly smaller species occurred during summer ( Dicrateria/Imantonia sp., Nephroselmis pyriformis, Ochromonas minima and others). From late August onwards Prorocentrum minimum occurred and formed a ‘red tide’ in Kiel Fjord. Based on their seasonal occurrence, temperature ranges are discussed for each species.

Use of 14C-protein-labelled bacteria for primary production

Three cultured species and mixed seawater communities of heterotrophc or mixotrophic flagellates were fed with non-cultivated aquatic bacteria labelled with I4C-protein hydrolysate, i.e. the method of radioactive labelled bacteria (RLB). Seawater bacteria incorporated protein-hydrolysate more rapidly and far more efficiently than 14~-glucose. Loss of label was less in the protein-labelled bacteria compared with those labelled with glucose. All tested flagellate species were found to ingest bacteria; individual clearance rates ranged from 0.014 $ ind.-' h-' (36 bacteria ind.-' h-'; Ochromonas minima) to 0.156 $ ind.-' h-' (156 bacteria ind.-' h-'; Paraphysomonas sp.). Uptake of bacteria by 0. minima and Bodo sp. was linear for ca 10 min, and levelled off between 10 to 40 min. Paraphysomonas sp. had a linear uptake for 20 min. Grazing rates obtained with 0. minima fed labelled bacteria and grazing rates calculated from chemostat culture were not significantly different. RLB proved rapid and efficient for estimating clearance by small heterotrophs and mixotrophs. Grazing rates in Bodo sp, and Paraphy- somonas sp, from a 'direct-count' method using DTAF-stained bacteria were 10 % of those obtained with RLR. RLB is shown to work well even with small size differences between predator and prey. This is obtained by use of pre-starved bacteria, which are reduced to a size where they may be separated from predators using a 1.0 pm filter. Field experiments with mixed seawater communities gave 10 to 30 times higher grazing rates using RLB compared to stained bacteria. The method accounts for food vacuoles containing bacteria, egested upon preservation of the bacterivory flagellates.

Oil pollution and plankton dynamics

The influence of Ekofisk crude oil on the development of natural flagellate communities was studied by means of polyethylene-bounded enclosures of coastal water masses in western Norway. The reaction to the pollution was most obvious at species level: Micromonas pusilla was not recorded in the upper 2 metres 12 days from start of the experiment, Emiliania huxleyi was absent or just about surviving, Nephroselmis pyriformis appeared to be indifferent to the pollution, whereas Ochromonas minima seemed to take advantage of the situation. Amoebae were common in the oil-polluted bag, though not recorded in the control. Addition of oil-dispersing agent Corexit 9527 changed the plankton community radically: Colourless flagellates and coccoid Chlorophyceae dominated, but total numbers were relatively small.