Phototrophic Picoplankton Research Articles

Have we overlooked the importance of small phytoplankton in productive waters?

The idea that phytoplankton size structure increases with elevated nutrient content in lakes may be inaccurate because phototrophic picoplankton (Ppico) abundance was not accounted for in studies that originally described this phenomenon. The biomass, composition, and production of an entire phytoplankton community was evaluated in hypereutrophic Lake Apopka, Florida (avg chlorophyll = 105 µg liter−1, n = 20) for 1 yr. Ppico cell abundances commonly exceed 107 cells ml−1, and size‐fractionated chlorophyll (<5 µm) and algal enumeration (cells <2 µm in size) indicate that pico‐size cyanobacteria contribute significantly to phytoplankton biomass throughout the year (avg 30%, n = 15), even though clogging of small pore‐sized filters used in chlorophyll fractionation studies led to underestimation of Ppico biomass estimates. Ppico production contributed nearly 30% (n = 8) to total phytoplankton production. The quantitative importance of Ppico in Lake Apopka and eight other hypereutrophic systems in Florida (avg 50% Chl <5 µm) indicates that Ppico can be important in waters of high nutrient content. The importance of small phytoplankton in productive waters may have been overlooked because (1) most studies focus on relatively pristine ecosystems, (2) some methodological constraints may impede studies in eutrophic environments (filtration artifacts), and (3) routine assessment of phytoplankton abundance rarely censuses all components of the community, including small algae.

Phototrophic picoplankton community structure in three different pelagic regimes in the Arabian Sea

Cell numbers and vertical distribution of Synechococcus, eucaryotic phototrophic picoplankton and prochlorophytes as determined by epifluorescence microscopy are presented from 3 different epipelagic systems (the mesotrophic coast off Oman, the oligotrophic central Arabian Sea and the shelf edge off Pakistan) in the Arabian Sea during the inter-monsoon period 1987. The vertical distribution patterns are described in relation to the epipelagic structure of the respective study sites. Synechococcus dominated phytoplankton in the upper mixed layer and prochlorophytes at the bottom of the euphotic zone in the lower part of and below the deep chlorophyll maximum High pressure liquid chromatography analysis confirmed the presence of prochlorophytes and revealed vertical profiles of characteristic pigments of picoplankton orgamsms, chlorophyll (chl) a and b, dmnyl chl a (chl a;) and zeaxanthin. Cellular pigment concentrations of Synechococcus and prochlorophytes are presented.

Microbial food webs and the export of biogenic carbon in oceans

Microbial food webs, which comprise phototrophic picoplankton (or ultraplankton), heterotrophic bacteria and protozoa, are ubiquitous in marine waters. Members of the microbial food web may play various roles in the export of biogenic carbon. For example, it has been postulated that high bacterial activity may sometimes prevent a significant fraction of the production by large phytoplankton from reaching metazoan consumers. Phototrophic or heterotrophic small plankton cells may be readily exported (i.e. biological CO2 pump) if incorporated into large particles, through either endosymbiosis with larger cells, or development on material accumulated in hydrodynamic traps, or inclusion into marine snow, or grazing by large planktonic microphages (e.g. salps) and incorporation in their sometimes fast-sinking faecal pellets. Another aspect is the export of carbonate by members of the microbial food web (e.g. coccolithophores, foraminifera), which influences the carbon dioxide balance of the ocean (i.e. carbonate pump). Finally, carbon bound into refractory dissolved organic matter is chemically sequestered in the upper ocean, before being exported to depth. The activity of microbial food webs may therefore influence in several ways the export (and sequestration) of biogenic carbon in oceans.

Primary production, biomass and abundance of phototrophic picoplankton in the Mediterranean Sea: a review

In the Mediterranean Sea, the contribution of picophytoplankton to primary production varies from 31% (Straits of Messina, with an average total production of 0.18 mg C m -3 h -1 ) to 92% (Ionian Sea, with an average of 1.64 mg C m -3 h -1 ). Although studies have used different methodologies, the contribution of this small phototrophic fraction to whole 14 C assimilation seems to be more important in oligotrophic off-shore waters (71%) compared to the neritic ones (44 %). Diluting effects of fluvial waters (Adriatic Sea) and hydrodynamic phenomena (Straits of Messina) probably influence the physiologic activity of these populations. Picophytoplankton contribution to primary production in brackish and eutrophic environment is clearly lower than in marine waters both in terms of chl a and of 14 C assimilation. Reports of cellular abundance (Cyanobacteria and eucaryotic cells) ranged from 10 5 to 10 8 cells l -1 with a mean value of 10 7 showing no difference between seasons and suggesting a state of particular equilibrium for this population in the planktonic community. Recent data on prochlorophyte cellular density are of the same order of magnitude (10 7 cells l -1 ) of other picophytoplanktonic procaryotic and eucaryotic organisms.

Succession of Pelagic Organisms in the Size Range 0·5-200 μm During a Diatom Bloom in Otsuchi Bay, Japan

The succession of pelagic organisms in the approximate size range 0·5-200 μm was investigated during a spring diatom bloom in Otsuchi Bay on the Pacific coast of northern Japan. The diatom bloom lasted 3 weeks in the middle of the period examined. The study period was divided into three phases: pre-bloom, bloom and post-bloom. Mesodinium rubrum, an autotrophic ciliate, was abundant in the pre-bloom phase, when vertical mixing was intense. During the bloom phase, the biomass of organisms other than diatoms themselves and bacteria was depressed. A bacterial peak was observed 4 days after the diatom peak and peaks of nano-autotrophs and -heterotrophs occurred after 14 days. Phototrophic picoplankton showed a biomass peak at the same time as nanoplankton. Grazing on diatoms by the copepod population was shown by the occurrences of faecal pellets and copepod nauplii during and after the bloom phase. These results suggest that production of copepods and bacteria depended only on the diatom bloom directly, and that heterotrophic micro-protista depended on the production of pico- and nano-autotrophs in the post-bloom phase.

Using frequency of dividing cells in estimating autotrophic picoplankton growth and productivity in the Chesapeake Bay

In situ incubations of natural autotrophic picoplankton populations during a 15 month study were used to test the frequency of dividing cells proceduresin estimating phototrophic picoplankton growth rates. These rates were estimated using dilution experiments and compared to the average frequency of dividing cells over the same time interval. The regression equation of µ = 2.85 × 10−3 (FDC) + 0.022 was calculated to relate autotrophic picoplankton growth rate and the frequency of dividing cells in this study. The resulting relationship was compared to 14C-bicarbonate derived growth rates. Productivity estimates using frequency of dividing cells correlated closely to sodium 14C-bicarbonate results and indicated a range of productivity by autotrophic picoplankton of 55.6% the total phytoplankton primary productivity in July to a January rate of 2.3%. Annual autotrophic picoplankton abundance varied seasonally in the lower Chesapeake Bay ranging from 7.26 × 106 cells 1−1 in winter to 9.28 × 108 cells 1−1 during late summer.

Seasonal Pattern of Phototrophic Picoplankton in the Eutrophic Coastal Waters of the Northern Adriatic Sea

The abundance and vertical distribution of picophytoplankton were investigated twice a month from March to December 1990, at two stations in the eutrophicated shallow waters of the Northern Adriatic sea. Cyanobacteria and autotrophic eukaryotic cells were enumerated by epifluorescence microscopy. High abundances of picophytoplankton were observed (3.8 × 10 7 cells L −1 , mean value) at both stations. Picophytoplankton cell numbers were highest in late spring-summer (2.3-3.8 × 10 8 cells L −1 ). Cyanobacteria outnumbered eukaryotes on average by nearly an order of magnitude; however, the ratio of eukaryotic picoplankton to cyanobacteria increased in autumn and winter (...)

Phototrophic Picoplankton in Lakes Huron and Michigan: Abundance, Distribution, Composition, and Contribution to Biomass and Production

The phototropic picoplankton communities of Lakes Huron and Michigan were studied from 1986 through 1988. Abundances in the surface-mixed layer ranged from 10 000 to 220 000 cells∙mL−1 with a seasonal maximum during the period of thermal stratification. During thermal stratification, maximum abundances were generally found within the metalimnion/hypolimnion at depths corresponding to the 0.6–6.0% isolumes. The picoplankton community was dominated by single phycoerythrin-containing (PE) Synechococcus (59%) with lesser amounts of chlorophyll fluorescing cells (21%), PE colonial Synechococcus-like cells (11%), other PE colonial Chroococcales (6%), and other cells (3%). Single PE Synechococcus was abundant throughout the year whereas chlorophyll-fluorescing and colonial cyanobacteria were more abundant during the periods of spring isothermal mixing and summer stratification, respectively. Picoplankton accounted for an average of 10% (range 0.5–50%) of phototrophic biomass. Phototrophic organisms that passed 1-, 3-, and 10-μm screens were responsible for an average of 17% (range 6–43%), 40% (21–65%), and 70% (52–90%) of primary production. Maximum contributions of < 1, < 3, and < 10 μm size fractions occurred during the period of thermal stratification. Primary production by phototrophic picoplankton was found to equal production in the < 1 μm size fraction.

Red Fluorescing Phototrophic Picoplankton in the Laurentian Great Lakes: What Are They and What Are They Doing?

AbstractEpifluorescence microscopy, flow cytometry, and transmission electron microscopy were used to characterize the community of red fluorescing (emission >665 nm when excited with blue light) phototrophic picoplankton (RFPP) in lakes Huron and Michigan. A population of coccoid to ovate eukaryotic cells with a mean size of 1.2 μm dominated the RFPP community in both surface and deep water samples. Abundant prochlorophyte populations were not found in any samples. Comparisons of counts with epifluorescence microscopy and flow cytometry, revealed that RFPP were adequately enumerated with standard epifluorescence microscopy. These RFPP were significant contributors to total phototrophic picoplankton abundance in both lakes Michigan (24%) and Huron (18%), with maximum seasonal abundance during the May‐June period (surface mixing layer temperatures, 3‐9 °C). During thermal stratification, maximum vertical abundance was found in the metalimnion/hypolimnion at the 1‐5% isolumes. RFPP were only minor contributors (1‐7%) to total primary production. Growth rates of RFPP measured with dilution and small inocula growth experiments ranged from 0.05‐1.0 d−1. Microzooplankton grazing rates on RFPP measured with dilution experiments were similar to estimated growth rates, accounting for 52‐280% of growth on any given date.

Net in situ growth rates of phytoplankton in an oligotrophic, tropical shelf ecosystem

In situ growth rates of phytoplankton in tropical shelf waters of the Great Barrier Reef were measured with diffusion chambers. A broad disparity was observed between the growth responses of diatom species or assemblages (µmax = 2–5 doublings d−1) and assemblages of microflagellates, nonmotile ultraplankton, or phototrophic picoplankton (µmax < 2 doublings d−1). Several diatom species or groups consistently grew faster than the community Chl doubling rate (µmax = 1.6 doublings d−1). Most dominant species and groups, regardless of taxonomic affiliation, exhibited the potential for high relative growth rates (µ/µmax > 0.5) at ambient concentrations of dissolved inorganic N <0.2 µmol liter−1 and the time‐averaged diurnal irradiances in situ >50 µEinst m−2 s−1. If relative constancy in phytoplankton standing crop and composition is to be maintained, grazing rates must vary widely at the species level, but be broadly similar to growth rates over time scales of days. Although the full 40–80‐m water column in the central Great Barrier Reef lies the euphotic zone, phytoplankton growth rates near the bottom seem to be light limited.

Preliminary study on vertical distribution of microorganisms in the Bannock Basin waters (Eastern Mediterranean Sea)

Preliminary study on vertical distribution of microorganisms in the Bannock Basin waters (Eastern Mediterranean Sea)

Phototrophic Picoplankton in Temperate Lakes: Seasonal Abundance and Importance along a Trophic Gradient

AbstractThe seasonal development of autotrophic picoplankton was investigated in seven Danish lakes representing a eutrophication gradient. Highest cell abundance between 1.5 to 6 × 105 cells ml−1 were found in mid‐summer. Minor peaks were observed in spring. In winter, densities were below 103 ml−1. The highest relative picoplankton contribution to total autotrophic biomass also occurred in mid‐summer. In the eutrophic lakes and one humic lake the average seasonal contribution of picoplankton to total chlorophyll was below 1% increasing to 5‐8% in the meso‐ and oligotrophic clear water lakes. During short periods the proportion of picoplankton did reach 25%. The higher relative importance of picoplankton in less productive lakes was not due to higher actual chlorophyll concentrations, but due to a much more pronounced response by larger algae at higher nutrient loading. Both cyanobacteria and eukaryote organisms were present as picoplankton. Only eukaryotes were found in one eutrophic lake and an acidic, humic lake. In the eutrophic lakes eukaryote picoplankton was dominant; both with respect to cell densities and biovolume, whereas cyanobacteria dominated the two meso‐oligotrophic lakes. Autotrophic picoplankton were present in all lake types, however their importance seemed to be less in most eutrophic lakes than in less productive, meso‐oligotrophic lakes.

Leaky Filters: A Warning to Aquatic Ecologists

We examined the retention characteristics of commonly used 0.2-μm nucleation-track (Nuclepore®, Poretics®), polymer (Millipore®, Sartorius®) and inorganic membrane (Anopore®) filters. Scanning electron micrographs of the filter surface showed many to contain large holes or pores, some 5 × larger than the manufacturer's stated nominal pore diameter. Electron micrographs of filtrates from both fresh and seawater samples contained a variety of organisms, including viruses, ultramicrobacteria, bacteria, phototrophic picoplankton, and larger nano- and microphytoplankton (e.g. diatoms), which we believe passed through the large openings. Total particles in the size range 1.0–12.8 μm passing through the various 0.2-μm filters tested ranged from 2.2 to 14.3%, with 'best' retention (>97%) by the Anopore®. Average particle retention for all 0.2-μm filters tested was 92.5%. Higher passage rates (lower retention) are predicted for even smaller (<1.0 μm) particles (prochlorophytes, bacteria, viruses) and investigators are urged to use care when using polycarbonate or matrix type filters for partitioning size fractions for chemical, physiological, and ecological work, and caution when interpreting results, especially if separations have not been verified by microscopy, incubation, or culture.

Seasonal and vertical distribution of picoplankton in Llyn Padarn, Gwynedd

The seasonal and vertical distribution of picoplankton was recorded, using epifluorescence microscopy, from October 1985 to September 1987. This size fraction was made up of red and orange autofluorescent coccoid cyanobacteria and heterotrophic bacteria. Bacterial numbers were high and fluctuated between a winter minimum of 4·0 × 104 cells ml-1 and a summer maximum of 1·8 × 106 cells ml-1. There was no correlation between bacterial cell number and water temperature. Orange fluorescent cells were the numerically dominant phototrophic picoplankton. Their numbers were lowest during winter (158 cells ml-1) and highest in late summer (1·0 × 105 cells ml-1). This seasonal fluctuation was paralleled by the red autofluorescent cells though their overall numbers were consistently less abundant, often by an order of magnitude, than those of the orange cells. During periods of high cell numbers, the autotrophic picoplankton contributed 5–15% of total picoplankton abundance. During periods of high total chlorophyll c...

Phototrophic picoplankton: An overview from marine and freshwater ecosystems

Algal picoplankton are a ubiquitous component of the microbial plankton communities of both marine and freshwater ecosystems. They contribute significantly to the total biomass of phytoplankton communities, and in oligotrophic oceans and lakes can be responsible for up to 80–90% of the total daily or annual carbon production. As part of the “microbial loop,” they are thought to be grazed by flagellates, ciliates, rotifers, copepods, and other metazoans, and contribute to the flow of energy to higher trophic levels. This presentation highlights their discovery, distribution, physiology, production, and contribution to pelagic food webs in marine and freshwater systems.

Phototrophic picoplankton: An overview from marine and freshwater ecosystems

Phototrophic picoplankton: An overview from marine and freshwater ecosystems

Biomass and photosynthetic activity of phototrophic picoplankton in coral reef waters (Moorea Island, French Polynesia)

In April 1984, chlorophyll a and photosynthetic activity of phytoplankton were measured above a coral reef and in the deep chlorophyll maximum (100m) of adjacent oligotrophic oceanic waters. Samples were frachonated into 3 sizes: 0.2-2. 2-5 and 2 5 km. Total chlorophyll a concentrahons were about 0.1 mg m-3, and phytoplankton > 5 pm never exceeded 104 cells I-'; picoplankton were not enumerated. Reef samples differed from oceanic waters by containing higher proportions of diatoms and lower proportions of coccolithophorids Chlorophyll biomass was dominated by the 20 mg C mg chl-' h-') occurred in the < 2 m subsequent grazing of small cells by corals and other constituents of the food web ('picoplankton loop'), may contribute to nutrient cycling within the reef ecosystem.

Picoplankton and Nanoplankton Biomass in Lake Ontario: Relative Contribution of Phototrophic and Heterotrophic Communities

The seasonal and vertical abundance of phototrophic and heterotrophic nanoplankton (2–20 μm) and picoplankton (0.2–2 μm) was estimated in Lake Ontario during 1982 by epifluorescence microscopy. Phototrophic and heterotrophic nanoplankton abundance differed by less than an order of magnitude and was typically present at densities of 103 cells∙mL−1. Heterotrophic nanoplankton was, on average, only half as abundant as phototrophic nanoplankton, but on several dates was more abundant than the latter. Both populations peaked in late June to early July. Phototrophic picoplankton, primarily chroococcoid cyanobacteria, increased rapidly during midsummer, reaching a maximum epilimnetic concentration of 4 × 105 cells∙mL−1 in late August. Heterotrophic picoplankton (bacteria) showed a similar seasonal pattern, reaching maximum abundance in September (6 × 106) cells∙mL−1). The concentrations of both picoplankton populations were significantly correlated with temperature. By late summer, picoplankton biomass represented 74% and pico-cyanobacteria alone 50% of the total weight biomass of microorganisms &lt; 20 μm; these populations are generally missed by inverted microscope techniques.

Algal Picoplankton from Marine and Freshwater Ecosystems: A Multidisciplinary Perspective

The discovery of minute (0.2–2.0 μm) algal picoplankton in the late 1970's in both marine and freshwater ecosystems has led to a resurgence of research activity throughout the world, addressing questions related to taxonomy, distribution and abundance, physiology and biochemistry, and ecological considerations of their role in aquatic food webs. To many, their discovery provided the "missing link" in the controversial carbon supply–demand question in the world's oceans and gave further credibility to the emerging new paradigm on the importance of microbial food webs in energy transfer and nutrient recycling in aquatic systems. In this essay we provide the first comprehensive multidisciplinary review of phototrophic picoplankton in lake and ocean ecosystems, discussing what is currently known about their occurrence, taxonomy, physiology, and biochemistry and their role in primary production and aquatic food webs.