Microbial Web Research Articles

Annual cycle of protozoan communities in an estuarine epibenthic sublittoral area

A protozoan community living in sandy marine sediments in a shallow sublittoral environment was studied in terms of diversity, density and biomass. Different abiotic parameters (granulometry, pH, temperature, dissolved oxygen, redox potential, salinity and conductivity) were recorded, as well as factors relating to nutrients (phosphate, nitrate, nitrite and organic matter). Bacterial biomass was also analyzed. The protozoan species were grouped as follows: ciliates, pigmented flagellates (AFLA), heterotrophic flagellates (HFLA), pigmented dinoflagellates (ADIN), heterotrophic dinoflagellates (HDIN) and sarcodines. Despite the fact that with regard to the relative frequencies of protozoan species, there were statistical differences between the sampling points, no significant differences existed when the protozoan groups were considered throughout the year. In addition, there were no differences with respect to surveys previously carried out in the same and neighbouring areas, and using the protozoan groups mentioned, which shows their stability. The trophic relations between these protozoan groups have been deduced from the data and the statistical results. The annual cycle appeared divided into four stages: herbivorous web (February–April), microbial loop (May–July), microbial web (August–October) and multivorous web (November–January).

The Canada-Japan SARES project on the first-year ice of Saroma-ko Lagoon (northern Hokkaido, Japan) and Resolute Passage (Canadian High Arctic)

Abstract A joint Canada-Japan project was conducted on the first-year ice of Saroma-ko Lagoon (northern Hokkaido, Japan) and Resolute Passage (Northwest Territories, Canada) during the winter and spring of 1992. Objectives of the SARES project were to (1) measure the activity of the biological CO 2 pump under the first-year sea ice and (2) characterized its main physical controls. The two study sites exhibit contrasting characteristics. Among others, Saroma-ko Lagoon is the southernmost area in the Northern Hemisphere with seasonal sea ice whereas Resolute Passage is one of the northernmost areas with recurrent first-year sea ice. It was hypothesized that such different characteristics would influence variables that determine the downward flux of biogenic carbon, e.g., hydrodynamics, nutrient replenishment, growth of ice algae and phytoplankton, transfer of primary production to the herbivorous and microbial webs, and sedimentation of biogenic particles. Measured variables included meteorology, hydrodynamics, primary production and nutrient effects, microbial web dynamics, production and grazing of zooplankton and ichthyoplankton, and sedimentation of algae and faecal pellets. The project involved 30 Canadian and 25 Japanese scientists, graduate students and technicians from seven institutions in Canada and twelve in Japan.

Plankton and nutrient dynamics in marine waters

Abstract Biological oceanographers generally distinguish between two contrasting trophic pathways in the pelagic environment, i.e. the herbivorous and the microbial food webs. The former goes from large phytoplankton and zooplankton to fish, whereas the latter comprises small eukaryotic algae and cyanobacteria as well as heterotrophic bacteria and protozoa. The present paper describes a continuum of trophic pathways, between systems dominated by the herbivorous food web and those dominated by the microbial loop (i.e. almost closed system of heterotrophic bacteria and zooflagel-late grazers, the latter releasing dissolved organic matter used as substrate by the bacteria). It is proposed that the continuum goes from the herbivorous web (or chain) to a “multivorous food web”, to the microbial web, and finally the microbial loop. Characteristics of the various pathways maybe summarized as a series of interconnected ratios. It is hypothesized that systems dominated by the herbivorous food web or the microbial ...

Rotifers as predators on components of the microbial web (bacteria, heterotrophic flagellates, ciliates) ? a review

Rotifers as predators on components of the microbial web (bacteria, heterotrophic flagellates, ciliates) ? a review

Seasonal Changes in the Plankton Dynamics of a Eutrophic Lake Including the Microbial Web

AbstractDuring 1989 and 1990 the carbon dynamics in the shallow eutrophic Lake Müggelsee (Berlin) were investigated by analysing the seasonal succession of phytoplankton, metazooplankton, protozooplankton and bacteria. Size fractionated algal primary production and exudation were measured as well as bacterial production in order to calculate the amount of carbon covering the bacterial carbon demand by primary production. The impact of bacterivorous protozoans and metazoans was estimated by comparison of the calculated feeding rate and the bacterial production. Our results show a shift within the metabolic interactions of the microbial food web from winter/spring to summer, indicating a high significance of the protozooplankton as a regulator on bacteria during the colder season, whereas from early summer the influence of metazooplankton dominated by cladocerans was evident in this eutrophic lake.

Large heterotrophic flagellates form a significant part of protozooplankton biomass in lakes and rivers

Abstract Stimulated by studies from marine waters there is now increasing evidence that the components of the microbial food web contribute to the pelagic flux of matter as significandy in freshwater environments as they do in the ocean. Up to now generally only heterotrophic nanoflagellates and cili-ates have been quantitatively considered among limnetic protozooplankton. Our investigations using a special live-counting technique showed that large heterotrophic flagellates (LHF, ≥ 15 μm; mainly chrysomonads and dinoflagellates) have been overlooked in quantitative estimations of limnetic protozooplankton biomass. We present estimations from 19 German lakes of different trophy during different seasons and from 4 rivers as well as detailed seasonal studies of a eutrophic lake and a brook indicating that LHF can form up to 50% (mean about one third) of protozooplankton biomass. LHF reached highest importance in early spring when LHF were one of the most significant herbivore groups. Large heterotrophic flagellates should be considered as significant components of limnetic food webs. This is in agreement with the present knowledge of marine pelagic ecosystems where LHF (mainly dinoflagellates) have already been recognized as an important part of the pelagic microbial web.

Spring clear-water phase in a eutrophic lake: Control by herbivorous zooplankton enhanced by grazing on components of the microbial web

Spring clear-water phase in a eutrophic lake: Control by herbivorous zooplankton enhanced by grazing on components of the microbial web

On the Importance of Planktonic Protozoans in the Eutrophication Process of the Baltic Sea

AbstractAnalysing the results of various authors recent studies in the pelagic region of the Baltic revealed that protozoan biomass is in the same range or even higher than metazooplankton biomass. The dominant groups of planktonic protozoans are heterotrophic pico‐ and nanoflagellates (various taxonomic groups), large heterotrophic flagellates (mainly dinoflagellates) and ciliates. Regularly the spring bloom of phytoplankton is accompanied by a maximum of protozoan biomass which declines in early summer as a result of intensive grazing pressure by metazooplankton and changing food conditions. The analysis of results from different stations indicated that biomasses of protozoans increase with an increasing degree of eutrophication. Several trophic levels within the microbial web should be added to the traditional view on the pelagic food web of the Baltic. Our knowledge regarding the quantitative aspect of the microbial matter flux of the Baltic is very limited up to now and complex ecological (and taxonomical) studies using standardized methods including all protozoan components are necessary. Protozoans (various trophic groups and levels), besides bacteria, should be viewed as the metabolically most active heterotrophic component in the pelagic region of the Baltic, their activity should increase with an increasing degree of eutrophication.