Planktonic microbes: Tiny cells at the base of the ocean's food webs

College of Oceanography, Oregon State University, Corvallis, OR 97331, USA.
Trends in Ecology & Evolution (Impact Factor: 16.2). 02/1991; 6(2):50-4. DOI: 10.1016/0169-5347(91)90122-E
Source: PubMed


Phytoplankton in the size range 5-100 μm was originally thought to be the primary source of food for most life in the sea. However, smaller planktonic microbes, down to 0.2 μm in size, have been the focus of intensive investigation by marine scientists during the past two decades. These microbes attain high abundance and biomass in all parts of the world ocean. They include non-photosynthesizing bacteria, at least two types of photosynthesizing prokaryotes, and eukaryotic phototrophs. The new information has resulted in a greatly revised concept of how pelagic ecosystems in both marine and freshwater environments function. The original idea of a basically linear food chain from diatoms to copepods to fish has given way to an extremely complex model of trophic interactions within a microbial food web, which supports metazoan food webs via biomass production of both heterotrophic and autotrophic cells.

10 Reads
  • Source
    • "Isotopic depletion extending into marine zooplankton grazers, a pathway mediated by the microbial food web [6], is a good proxy for food web modification by the spill. Here we 3 Author to whom any correspondence should be addressed. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The Deepwater Horizon oil spill was unprecedented in total loading of petroleum hydrocarbons accidentally released to a marine ecosystem. Controversial application of chemical dispersants presumably accelerated microbial consumption of oil components, especially in warm Gulf of Mexico surface waters. We employed δ13C as a tracer of oil-derived carbon to resolve two periods of isotopic carbon depletion in two plankton size classes. Carbon depletion was coincident with the arrival of surface oil slicks in the far northern Gulf, and demonstrated that subsurface oil carbon was incorporated into the plankton food web.
    Full-text · Article · Nov 2010 · Environmental Research Letters
  • Source
    • "Heterotrophic flagellated nanoplankton (HFN) HFN of the Sfax slatern were larger (8 –12 mm) than those found in marine (2 – 5 mm, Sherr & Sherr, 1991), estuarine (4 mm, Gilbert, 2001) and freshwater (2 and 6 mm, Domaizon et al., 2003) ecosystems. The highest density of HFN was recorded in the hyper-saline ponds where they contributed 50% of total nanoplankton contrary to Pedrós-Alió et al. (2003) who showed that HFN decreased with salinity and disappeared when salt concentration was higher than 300‰. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The distribution of abundance and biomass of prokaryotes, flagellates, ciliates and phytoplankton, were studied in five ponds of increasing salinity in the Sfax solar saltern (Tunisia) coupled with environmental factors. The results showed that abundance of eukaryotic microorganisms decreased with increasing salinity of the ponds whereas prokaryotes (heterotrophic bacteria and Archaea) were abundant in the hyper-saline ponds. Phototrophic picoplankton was found in a large range of salinity values (70 and 200‰). Phototrophic non-flagellated nanoplankton which dominated in the first sampled pond was substituted by phototrophic flagellated nanoplankton in the other ponds. Heterotrophic nanoplankton dominated in the crystallizer pond but its quantitative importance declined in the less saline ponds. Diatoms and dinoflagellates were the major contributors to phytoplankton abundance in the first ponds (>90% of total abundance). Ciliated protozoa were found in all the ponds except in the crystallizer in which prokaryotes proliferated. Oligotrichida and Heterotrichida were the most abundant ciliate groups. Overall, species richness decreased with salinity gradient. We propose a simplified diagram of the Sfax saltern's food web showing the dominant role of the microbial loop along the salinity gradient.
    Full-text · Article · Feb 2009 · Journal of the Marine Biological Association of the UK
  • Source
    • "This level also matches a previous mortality estimate of bacterioplankton caused by protozooplankton in the Bothnian Sea area (Wikner & Hagström 1991) b Bacterial diet was assumed to be DOC c Wikner & Hagström (1988, 1991) have estimated that 90% of the carbon demand by bactivorous flagellates (1–5 µm) consist of picoplankton (similarly: Kuuppo-Leinikki 1990, Sherr & Sherr 1991). It was assumed that 70% of this constituted bacteria and 20% cyanobacteria (Hagström et al. 1988) d Prey size spectrum based on results from Rassoulzadegan & Sheldon (1986), Wikner & Hagström (1988), Sherr & Sherr (1991) and Dolan & Gallegos (1991) e Prey size spectrum based on results from Rassoulzadegan & Sheldon (1986), Wikner & Hagström (1988), Sherr & Sherr (1991) and Dolan & Gellegos (1991) f Prey size spectrum based on results from Fenchel (1980), Jonsson (1986), Rassoulzadegan et al. (1988), Verity & Villareal (1986) and Dolan & Gellegos (1991). These prey size spectra agree with findings in the Gulf of Finland (Kivi et al. 1996), where ciliates have strong regulating effects on prey <10 µm in presence of zooplankton g Following Kivi et al. (1996), besides large phytoplankton >10 µm, microzooplankton (e.g. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The objective of this study was to quantitatively assess the relative importance of terrigenous dissolved organic material (TDOC) as a carbon source for secondary producers (e.g. bacteria) and as a structuring factor for the pelagic food web in the Gulf of Bothnia, northern Baltic Sea. The 3 study sites, situated in Bothnian Bay (BB), the Ore Estuary (OE) and the Bothnian Sea (BS), had markedly different freshwater loads and water-residence times. In Bothnian Bay, bacterial biomass and production were higher than expected from the levels of phytoplankton biomass and productivity there, suggesting an uncoupling of bacterial productivity from phytoplankton production. Phytoplankton size structure and size-fractionated production were, however, relatively similar among areas. A simplified carbon budget model suggested that bacterioplankton dominated organic carbon consumption in all of the food webs studied, but was most marked in BB. The model showed that the available autochthonous primary production could not alone support the heterotrophic carbon demand in BB. The most likely explanation of this discrepancy was that the total annual input of terrigenous dissolved organic carbon was bioavailable, resulting in a budget closer to balance with the heterotrophic carbon demand. BB, receiving 38% of the carbon input from land, was consequently a net heterotrophic ecosystem. A sensitivity analysis showed that the bacterial carbon demand, and growth efficiency in particular, had the greatest influence on the resulting budget. TDOC was the dominant Carbon source in OE, but the losses Of Carbon through advection to offshore areas and sedimentation was high. The evidence of net heterotrophy in OE was therefore weaker than in BB. In BS the input of TDOC was less important, and the carbon used for secondary production originated mainly from autochthonous primary production. Our results suggest that the supply of TDOC is of great importance for the abundance of plankton and as a structuring factor for the aquatic food webs in the Gulf of Bothnia.
    Full-text · Article · Mar 2004 · Marine Ecology Progress Series
Show more