Phototrophic Nanoplankton Research Articles

Bacterivory by phototrophic picoplankton and nanoplankton in Arctic waters

Mixotrophy, the combination of phototrophy and heterotrophy within the same individual, is widespread in oceanic systems. Yet, neither the presence nor ecological impact of mixotrophs has been identified in an Arctic marine environment. We quantified nano- and picoplankton during early autumn in the Beaufort Sea and Canada Basin and determined relative rates of bacterivory by heterotrophs and mixotrophs. Results confirmed previous reports of low microbial biomass for Arctic communities in autumn. The impact of bacterivory was relatively low, ranging from 0.6 × 10(3) to 42.8 × 10(3) bacteria mL(-1) day(-1) , but it was often dominated by pico- or nanomixotrophs. From 1% to 7% of the photosynthetic picoeukaryotes were bacterivorous, while mixotrophic nanoplankton abundance comprised 1-22% of the heterotrophic and 2-32% of the phototrophic nanoplankton abundance, respectively. The estimated daily grazing impact was usually < 5% of the bacterial standing stock, but impacts as high as 25% occurred. Analysis of denaturing gradient gel electrophoresis (DGGE) band patterns indicated that communities from different depths at the same site were appreciably different and that there was a shift in community diversity at the midpoint of the cruise. Sequence information from DGGE bands reflected microbes related to those from other Arctic studies, particularly from the Beaufort Sea.

Krill larvae, copepods and the microbial food web: interactions during the Antarctic fall

Experiments were run in the Antarctic Bellinghausen Sea during the austral fall to ascertain the interactive effects of krill larvae (furcilia) and copepods on the microbial food web. A cross-classi- fied design with addition of the small cyclopoid cope- pod Oithona similis and either the furcilia larvae of Euphausia superba or the calanoid copepod Metridia gerlachei to the natural planktonic community was used, as well as a single experiment with varying den- sities of O. similis. The experiments showed furcilia to have much higher grazing rates on copepods and cili- ates than on algae, with positive selection for ciliates that was not influenced by the presence or absence of O. similis. M. gerlachei had a grazing impact on cili- ates that was much less than that of furcilia larvae, but due to a high taxonomic resolution of the ciliate community it could be shown that there were groups of grazing-vulnerable and -resistant forms. Contrary to expectations, O. similis had very low grazing rates on both ciliates and algae, but here too grazing-vul- nerable and -resistant groups of ciliates could be dis- tinguished. Neither the very strong impact of furcilia on ciliates, copepods and algae nor the more moder- ate impact of M. gerlachei cascaded down to hetero- trophic and phototrophic nanoplankton or to bacteria. At least at the time of our experiments, ciliates were tightly bound to the 'classic' aquatic food web, but do not serve to transmit a trophic cascade from the clas- sic and microbial food webs.

Do mucilage events influence pico- and nanoplankton size and structure in the Adriatic sea?

Temporal changes in abundance and biomass of picophytoplankton, heterotrophic pico-eukaryotes, and nanoplankton assemblages were investigated along a transect crossing the Adriatic Sea, from the Italian to the Croatian coast. This 15-months (June 1999–August 2000) investigation allowed comparing microbial parameters during summer 1999 (year without mucilage) and summer 2000 when a major mucilage event occurred. Pico- and nanoplankton assemblages displayed significant differences between the 2 summer periods. The main differences can be summarized as: (i) presence of cyanobacterial blooms (up to 108 cells l−1) in summer 2000, absent in summer 1999; (ii) an increasing fraction of heterotrophic pico-eukaryotes (up to 5.0 × 106 cells l−1) and heterotrophic nanoplankton (size 2–5 µm) during mucilage event; (iii) a reduced abundance of small-sized (2–3 µm) phototrophic nanoplankton in summer 2000. Changes in community structure were signals of changes in trophic condition of the system, which resulted in a competitive advantage for small sized pico- and nanoheterotrophs. Data presented here indicated that mucilage events are associated with changes in microbial community structure and functioning in ambient water and induced the amplification of 3-step microbial food chain. The potential use of the heterotrophic pico-eukaryotes for describing alterations of the trophic pathways during mucilage events is discussed.

Heterotrophic and mixotrophic nanoplankton predation on picoplankton in the Sargasso Sea and on Georges Bank

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 192:103-118 (2000) - doi:10.3354/meps192103 Heterotrophic and mixotrophic nanoplankton predation on picoplankton in the Sargasso Sea and on Georges Bank Robert W. Sanders1,*, Ulrike-G. Berninger2, Ee Lin Lim3,**, Paul F. Kemp4, David A. Caron3,*** 1Department of Biology, Temple University, Philadelphia, Pennsylvania 19122, USA 2Institut für Meereskunde, Abteilung Meeresbotanik, Düsternbrooker Weg 20, 24105 Kiel, Germany 3Department of Biology, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA 4Marine Sciences Research Center, State University of New York, Stony Brook, New York 11794, USA *E-mail: rsanders@nimbus.ocis.temple.edu Present addresses: **Department of Biology. Temple University, Philadelphia, Pennsylvania 19122, USA ***Department of Biological Sciences, University of Southern California, Los Angeles, California 90089, USA ABSTRACT: Nanoplankton and picoplankton abundance and community grazing on picoplankton were determined in summer and autumn at several stations in a productive coastal environment (Georges Bank, NW Atlantic Ocean) and in an oligotrophic oceanic ecosystem (Sargasso Sea). Ranges of heterotrophic nanoplankton (HNAN) abundance were 1.2 to 3.6 x 103 cells ml-1 on Georges Bank, and 2.2 to 6.8 x 102 cells ml-1 in the Sargasso Sea. Ranges of phototrophic nanoplankton (PNAN) abundance in these ecosystems were 1.9 to 6.0 x 103 and 1.3 to 4.7 x 102, respectively. Mixotrophic nanoplankton (MNAN), operationally defined here as chloroplast-bearing nanoplankton that ingested fluorescent tracers, comprised an average of 12 to 17% of PNAN in surface waters in both environments during August and October. Mixotrophs at specific stations constituted as much as 38% of total PNAN abundance on Georges Bank and 30% in the Sargasso Sea. Mixotrophs represented up to 39% of the total phagotrophic nanoplankton abundance (MNAN/[MNAN + HNAN]). Community grazing impact was estimated from the disappearance of fluorescent prey surrogates (fluorescently labeled bacteria, FLB; cyanobacteria, FLC; and <\3 µm algae, FLA). Absolute grazing rates (total picoplankton cells removed d-1) on Georges Bank exceeded those in the Sargasso Sea due to the greater abundances of predators and prey. However, there was overlap in the specific grazing losses at the 2 sites (ranges = 0.08 to 0.38 d-1 in the coastal ocean and 0.05 to 0.24 d-1 in the oligotrophic ocean). Rates of bacterivory were in approximate balance with rates of bacterial production (3H-thymidine uptake), but production exceeded bacterivory on Georges Bank during the summer cruise. These data are among the first documenting the impact of grazing on picoplankton in these environments, and they are consistent with the prediction that nanoplanktonic protists are major predators of picoplankton. While the proportion of phototrophs that are phagotrophic was highly variable, our study indicates that algal mixotrophy is widespread in the marine environment, occurring in both coastal and oligotrophic sites, and should be considered quantitatively in microbial food web investigations. KEY WORDS: Nanoplankton/picoplankton interactions · Mixotrophy · Bacterivory · Herbivory · Microbial food web · Flagellates · Cyanobacteria Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 192. Publication date: January 31, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Composition and biomass of plankton in spring on the Cape Hatteras shelf, with implications for carbon flux

The Ocean Margins Program, an interdisciplinary study focussed at Cape Hatteras, is evaluating whether this region is a net source or sink for carbon, while concurrently developing a mechanistic understanding of the production, cycling and fate of organic carbon. Preliminary to a large multi-ship field program in 1996–1997, the first of several short cruises surveyed Cape Hatteras in May 1993. High concentrations of chl a occurred across the shelf. Stations and depths at which chl a was highest also showed elevated concentrations of large phytoplankton, predominantly chained diatoms, but also single-celled dinoflagellates and obligately photosynthetic ciliates. These populations occurred in deeper waters, however, and their abundance was poorly correlated with proxies of community photosynthesis. Instead, small phototrophic nanoplankton, abundant in surface waters, were positively correlated with primary production. Carbon budgets indicated that inner shelf waters contained ca 50% more living POC than outer shelf waters. The relative importance of large phytoplankton and grazers decreased with distance offshore, and they were replaced by photosynthetic nanoplankton and microzooplankton. Even greater changes in living POC occurred in the alongshore direction due to the dramatic reductions in diatoms in southern waters. Estimated herbivory was ca 2–4 gC m −2 d −1. The ratio of heterotrophic : autotrophic POC increased from 38% in northern waters to 137% in southern waters, suggesting that phytoplankton was being converted into consumer carbon as shelf waters advected south. The dominant consumers at most stations were single-celled protozoan zooplankton and small copepods, whose fecal products remain in suspension in energetic shelf environments, suggesting that much of the non-diatomaceous POC was exported as shelf waters exited at Cape Hatteras.

The contribution of microorganisms to particulate carbon and nitrogen in surface waters of the Sargasso Sea near Bermuda

Seawater samples were collected from the euphotic zone of the Sargasso Sea near Bermuda in August of 1989 and March–April of 1990. Microbial population abundances, chlorophyll concentration, particulate carbon and particulate nitrogen were measured. Calculations were performed to establish the relative and absolute importance of the various microbial assemblages. The choice of conversion factors (g C and N cell−1, or g C and N μm−3) for the microbial populations dramatically affected the estimation of “living” and “detrital” particulate material in the samples, and the relative importance of the various microbial groups. Averaged over all samples on either of the two cruises, microbial biomass constituted a greater proportion of the total particulate carbon and nitrogen during March–April (55% and 63%, respectively), than during August (≈24% and 30%, respectively) using “constrained” conversion factors that were derived. Accordingly, detrital material constituted the bulk of the particulate material during August, but was similar to the amount of microbial biomass during March–April. The bacterial assemblage constituted the largest single pool of microbial carbon (35%) and nitrogen (45%) in the water, and a significant fraction of the total particulate carbon (≈10–20%) and nitrogen (≈15–30%). Phototrophic nanoplankton (microalgae 2–20 μm in size) were second in overall biomass, and often dominated the microbial biomass in the deep chlorophyll maxima that were present during both cruises. The results temper recent assertions concerning the overwhelming importance of bacterial biomass in the oligotrophic Sargasso Sea but still support a major role for these microorganisms in the open ocean as repositories for carbon and nutrients.

Grazing by rotifers and crustacean zooplankton on nanoplanktonic protists

Predation on nanoflagellates by metazoan zooplankton was investigated using a radioactively labeled flagellate, Poterioochromonas malhamensis, as a tracer cell in laboratory incubations of freshly collected plankton assemblages. Experiments conducted in the fall, winter and spring indicated that rotifers dominated the grazing on nanoflagellates by metazoans in the winter (68%) and spring (92%). Rotifer grazing was not determined in the autumn. It is likely that the greater impact of rotifer grazing in the spring was due to the occurrence of abundant filamentous cyanobacteria and gelatinous colonial phytoplankton which selectively depressed feeding rates of crustaceans compared to rotifers. Crustacean predation on nanoflagellates was highest in the autumn when cladocerans (primarily Daphnia spp.) were abundant. Predation by metazoan zooplankton in this lake appeared capable of removing the total standing stock of heterotrophic and phototrophic nanoplankton in < 1 d. Impacts of ciliated protozoa on nanoplankton, calculated from abundances and literature feeding rates, ranged from approximately one-third to four times that of metazoan predation depending on season and method of calculation. The relative importance of the different groups of predators appears to vary seasonally which is expected to alter the transfer of energy, carbon and nutrients from bacteria to higher trophic levels.

Mixotrophic algae in three ice‐covered lakes of the Pocono Mountains, U.S.A.

SUMMARY1. The occurrence and grazing activity of mixotrophic (phagotrophic) algae in three icecovered freshwater lakes of different trophic status were examined (oligotrophic Lake Giles, mesotrophic Lake Lacawac, eutrophic Lake Waynewood), Microbial population densities were low (4.1–7.2 × 105 bacteria ml−1 and 1.2–2.4 × 103 nanoplanktonic protists ml−1). All three nanoplankton communities were dominated by chloroplast‐bearing forms (60–96%).2. Mixotrophs formed up to 48% of the phototrophic nanoplankton in Lake Lacawac and were responsible for up to ∼90% of the observed uptake of bacteria‐sized particles. The abundance of mixotrophic algae in Lakes Giles and Waynewood were extremely low (3 and 2% of the phototrophic algae, respectively), and heterotrophs dominated nanoplankton bacterivory.3. The overall impact of nanoplankton feeding activity on the bacterial assemblage was low under the ice in Lakes Giles and Waynewood. Removal rates of bacteria based on our particle uptake experiments were 1.0 and 4.0% of the bacterial standing stock day−1 in these lakes, respectively. Removal rates were higher in Lake Lacawac and ranged from 4.9 to 11% of the bacterial standing stock day−1 on 2 successive sampling days.

On the abundance and distribution of protozoa and their food in a productive freshwater pond

We have examined and quantified the protozoa living in a productive freshwater pond during a 2-day period in June 1987. Over 90 species were recognised. The planktonic and benthic communities were dominated by ciliates and heterotrophic flagellates although the large amoeba Pelomyxa palustris was abundant (102 ml(-1)) in anaerobic sediments. Picoplankton averaged 1.4 × 10(7) ml(-1), phototrophic nanoplankton 0.8 × 10(5) ml(-1), heterotrophic nanoplankton 0.9 × 10(5) ml(-1) and planktonic ciliates 1.3 × 10(2) ml(-1). Numbers were about two orders of magnitude higher in the sediment. Protozoan biomass ranged from 3% to 61% of the total plankton biomass. Heterotrophic flagellates were the principal grazers of the picoplankton. Planktonic ciliates fed mainly on phototrophic nanoplankton but they probably also ingested heterotrophic flagellates. Benthic ciliates were predominantly bactivorous. Competition between ciliate species was minimised by both spatial and food niche separation. Ten species of planktonic ciliates appeared to contain algal symbionts: one species (Strombidium viride) contained structures resembling sequestered chloroplasts. These findings concerning the diversity and abundance of protozoa in a freshwater pond are consistent with the consensus opinion expressed in the marine literature that protozoa play a fundamental role in microbial food webs within aquatic ecosystems.

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.

Grazing of phototrophic nanoplankton by microzooplankton in Narragansett Bay

Grazing of phototrophic nanoplankton by microzooplankton in Narragansett Bay

Abundance and productivity of heterotrophic nanoplankton in Georgia coastal waters

The population abundances and rates of biomass production of heterotrophic nanoplankton (HNAN) in Georgia coastal waters were evaluated by epifluorescence microscopy. HNAN populations (mostly non-pigmented microflagellates <10 μm in diameter) ranged from 0.3 × 10 3 cells ml −1 in shelf waters 15 km offshore to 6.3 × 10 3 cells ml −1 in waters 0.25 km from the coast. There was a strong correlation ( r = 0.83) between HNAN and free bacterioplankton population abundances, but no apparent relation ( r = 0.38) between HNAN and phototrophic nanopLankton (PNAN) abundances. HNAN biomass production in estuarine and nearshore shelf waters, as estimated from increases in HNAN populations during laboratory incubations of natural water samples, ranged from 0.10 to 0.79 mg C m −3 h −3 , with population generation times of 9.7 to 26.5 h. There was a significant linear relation ( r = 0.95) between HNAN biomass and HNAN productivity. We calculated that HNAN may graze at least 30% to 50% of daily bacterioplankton production in Georgia coastal waters.

Technique for Enumeration of Heterotrophic and Phototrophic Nanoplankton, Using Epifluorescence Microscopy, and Comparison with Other Procedures

A new method is described that uses the fluorochrome primulin and epifluorescence microscopy for the enumeration of heterotrophic and phototrophic nanoplankton (2 to 20 mum). Phototrophic microorganisms are distinguished from heterotrophs by the red autofluorescence of chlorophyll a. Separate filter sets are used which allow visualization of the primulin-stained nanoplankton without masking chlorophyll a fluorescence, thus allowing easy recognition of phototrophic cells. Comparison with existing epifluorescence techniques for counting heterotrophic and phototrophic nanoplankton shows that primulin provides more accurate counts of these populations than the fluorescein isothiocyanate or proflavine techniques. Accuracy is comparable to that with the acridine orange technique, but this method requires only one filter preparation for the enumeration of both phototrophic and heterotrophic populations.

Dependence of dissolved carbohydrate concentrations upon small scale nanoplankton and bacterioplankton distributions in the western Sargasso Sea

Significant correlations between trophic components of the <20 μm microbial plankton and the concentrations of total dissolved carbohydrate (TCHO) and polysaccharide (PCHO) have been found at two drogued buoy stations which were sampled at 3 or 4-h intervals over diel cycles. An attempt was made to sample on two pre-selected isotherms (approximating isopycnals) at each station. Significant inverse correlations of TCHO and of PCHO with numbers of phototrophic nanoplankton (PNAN) were found along both isotherms at a station off the Carolina coast. Off central Florida, TCHO and/or PCHO were significant multiple linear functions of PNAN, heterotrophic bacterioplankton (BAC) and sometimes heterotrophic nanoplankton (HNAN) counts. Partial regression coefficients for PNAN were always negative and those for HNAN were positive. Inverse trends dominated the relations of BAC with PCHO and TCHO. The combined data from the two stations (300 nautical miles apart) produced very similar multiple linear relations. This suggests that the observed relationships are real, resulting from general physiological processes and interactions of the microbial plankton groups rather than from chance occurrences at a particular station, and that the combined activities of the <20 μm plankton actively regulate dissolved carbohydrate concentrations in the Sargasso Sea.