Predation on Protozoa: its importance to zooplankton
TL;DR: Evaluation de l'importance potentielle des protozoaires comme source de nourriture pour le zooplancton and les larves de poissons.
Abstract: Evaluation de l'importance potentielle des protozoaires comme source de nourriture pour le zooplancton et les larves de poissons
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TL;DR: In this article, the authors studied the impact of predation by protists on the community structure of prey assemblages and of chemical communication between predator and prey in microbial food webs.
Abstract: Predation in aquatic microbial food webs is dominated by phagotrophic protists, yet these microorganisms are still understudied compared to bacteria and phytoplankton. In pelagic ecosystems, predaceous protists are ubiquitous, range in size from 2 µm flagellates to >100 µm ciliates and dinoflagellates, and exhibit a wide array of feeding strategies. Their trophic states run the gamut from strictly phagotrophic, to mixotrophic: partly autotrophic and partly phagotrophic, to primarily autotrophic but capable of phagotrophy. Protists are a major source of mortality for both heterotrophic and autotrophic bacteria. They compete with herbivorous meso- and macro-zooplankton for all size classes of phytoplankton. Protist grazing may affect the rate of organic sinking flux from the euphotic zone. Protist excretions are an important source of remineralized nutrients, and of colloidal and dissolved trace metals such as iron, in aquatic systems. Work on predation by protists is being facilitated by methodological advances, e.g., molecular genetic analysis of protistan diversity and application of flow cytometry to study population growth and feeding rates. Examples of new research areas are studies of impact of protistan predation on the community structure of prey assemblages and of chemical communication between predator and prey in microbial food webs.
723 citations
Journal Article•
TL;DR: Inadequate understanding of the true abundance, biomass, trophic ecology, and role of small copepods in biogenic fluxes precludes properUnderstanding of the ecology of the sea.
Abstract: Small planktonic marine copepods (＜ 1 mm in length) are the most abundant metazoans on Earth. Included are adults and copepodites of calanoid genera such as Paracalanus, Clausocalanus, and Acartia; cyclopoid genera such as Oithona, Oncaea, and Corycaeus; planktonic harpacticoids of the genus Microsetella; and nauplii of almost all copepod species. Despite the abundance of small copepods, they have historically been undersampled due to the use of nets with meshes ＞ 200- 333 μm. Recent studies have shown, however, that when appropriate net meshes of 100 μm or less are used, small copepods vastly exceed the abundance and sometimes the biomass of larger ones. Failure to adequately account for small copepods may cause serious underestimations of zooplankton abundance and biomass, the copepod grazing impact on phytoplankton primary production, zooplankton-mediated fluxes of chemicals and materials, and trophic interactions in the sea. The feeding ecology of small copepods is less well-known than that of adults of larger copepod species, such as members of the genus Calanus. Further, most feeding information for small copepods is for coastal genera such as Acartia, rather than for offshore taxa. Although it is generally assumed that small copepods, including nauplii, feed primarily upon small-sized phytoplankton cells, most such information comes from rearing or feeding studies on limited laboratory diets. There have been few examinations of actual copepod feeding on mixed diets of natural phytoplankton and microzooplankton found in the sea, but some of those have produced surprises. For instance, some species of Oithona and Paracalanus and even nauplii of Arctic Calanus spp. may feed primarily as predators upon heterotrophic protists, rather than as grazers of phytoplankton. Also, nauplii of various tropical copepod species have been shown to feed upon bacterioplankton. Thus, numerous basic questions remain as to the feeding ecology and grazing/predation impact of small copepods in the sea. Despite limited knowledge of what small copepods eat, it is clear that many higher-trophic-level consumers eat them. Numerous studies have shown that copepod nauplii, Oithona spp., and other small copepods are important prey of fish larvae and other planktivores. Small copepods exhibit a variety of reproductive strategies to compensate for losses to their populations due to predation. These include having high fecundity and growth rates, when not limited by insufficient food; having high reproduction and growth rates at warmer temperatures; having limited motion and low respiration rates, allowing the investment of more energy in reproduction; and having extended longevity to maximize lifetime reproductive output. Thus, small copepods are important links in marine food webs, serving as major grazers of phytoplankton, as components of the microbial loop, and as prey for ichthyoplankton and other larger pelagic carnivores. Our present inadequate understanding of the true abundance, biomass, trophic ecology, and role of small copepods in biogenic fluxes precludes proper understanding of the ecology of the sea.
647 citations
TL;DR: The notion that the relationshp between feeding and production in copepods is driven by clletary diversity is derived in part from a recent recognition of the diversity of microplanktonic organisms that potentially or actually contribute to the diet.
Abstract: A review of the literature (ca 1900 to 1992) on copepod feeding indicates that combinations of stochashc and deterministic processes result in behaviors, or feeding strategies, that optirnize nutritional gain from the food environment, and further, that strategies change in response to environmental variability. Because the diet is the product of a feeding strategy, one may gain insight into the ways in which copepods respond to their food environments by measuring their diets. Investigations of the hnks between copepod feeding and production suggest that dietary diversity is often a key to the procurement of a nutritionally complete ration, and the optimization of secondary production within constraints dictated by the physical environment. The ability to eat different kinds of foods (ornnivory) and the tendency to include a variety of foods in the daily ration may enhance the probabhty of obtaining a nutritionally complete ration in variable, nutritionally dilute, food environments. The notion that the relationshp between feeding and production in copepods is driven by clletary diversity is derived in part from a recent recognition of the diversity of microplanktonic organisms that potentially or actually contribute to the diet. Further, the concept is consistent with current trophic dynamic models in which food webs are envisioned as complex interwoven systems rather than short, simple chains.
545 citations
Cites background from "Predation on Protozoa: its importan..."
...…The particles that copepods eat vary in nutritional microzooplankton and other kinds of particles - one composition (Parsons et al. 1977, Hitchcock 1982, must then ask, 'What adaptive advantage does a di- Stoecker & Capuzzo 1990) and feeding strategies verse diet have over a narrow one?...
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...Protozoans are abundant in the sea and may consume a large portion of the daily primary production (Pomeroy 1974, Capriulo & Carpenter 1980, Banse 1982, Sherr et al. 1986, Stoecker & Capuzzo 1990, Gifford 1991, Lessard 1991)....
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...However, significant (Stoecker & Egloff 1987, Stoecker & Capuzzo 1990). changes in the proportions of plant and animal bioProtozoans that ingest nano- and picoplankton may, in mass in the diet (rather than shifts from one extreme turn, be preyed upon by mesozooplankton, transfer- to the other) have…...
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TL;DR: This work explores current knowledge of the processing of zooplankton food ingestion by absorption, egestion, respiration, excretion, and growth (production) processes and examines the relative importance, combined magnitude, and efficiency of export mechanisms.
Abstract: Marine zooplankton comprise a phylogenetically and functionally diverse assemblage of protistan and metazoan consumers that occupy multiple trophic levels in pelagic food webs. Within this complex network, carbon flows via alternative zooplankton pathways drive temporal and spatial variability in production-grazing coupling, nutrient cycling, export, and transfer efficiency to higher trophic levels. We explore current knowledge of the processing of zooplankton food ingestion by absorption, egestion, respiration, excretion, and growth (production) processes. On a global scale, carbon fluxes are reasonably constrained by the grazing impact of microzooplankton and the respiratory requirements of mesozooplankton but are sensitive to uncertainties in trophic structure. The relative importance, combined magnitude, and efficiency of export mechanisms (mucous feeding webs, fecal pellets, molts, carcasses, and vertical migrations) likewise reflect regional variability in community structure. Climate change is expe...
457 citations
Cites background from "Predation on Protozoa: its importan..."
...Most copepods operate as omnivorous suspension feeders that prey broadly on heterotrophic protists, small animals (e.g., eggs and nauplii), and likely detritus, in addition to phytoplankton (Sherr et al. 1986, Stoecker & Capuzzo 1990, Calbet & Saiz 2005)....
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TL;DR: It is known that a significant fate of bacterioplankton production is grazing by < 20-µm-sized flagellates, which indicates that bacterivores may be directly cropping bacterial production rather than simply the standing stock of bacterial cells.
Abstract: Research on “microbial loop” organisms, heterotrophic bacteria and phagotrophic protists, has been stimulated in large measure by Pomeroy's seminal paper published in BioScience in 1974. We now know that a significant fate of bacterioplankton production is grazing by 20-µm ciliates and heterotrophic dinoflagellates in the microzooplankton. Protists can grow as fast as, or faster than their phytoplankton prey. Phototrophic cells grazed by protists range from bacterial-sized prochlorophytes to large diatom chains (which are preyed upon by extracellularly-feeding dinoflagellates). Recent estimates of microzooplankton herbivory in various parts of the sea suggest that protists routinely consume from 25 to 100% of daily phytoplankton production, even in diatom-dominated upwelling blooms. Phagotrophic protists should be viewed as a dominant biotic control of both bacteria and of phytoplankton in the sea.
454 citations
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TL;DR: The results suggest the involvement of PUFAs in the maintenance of optimal membrane fluidity and function over environmentally relevant temperatures and pressures and an important, specific role for deep-sea bacteria in abyssal food webs is implicated.
Abstract: The fatty acid composition of the membrane lipids in 11 deep-sea bacterial isolates was determined. The fatty acids observed were typical of marine vibrios except for the presence of large amounts of long-chain polyunsaturated fatty acids (PUFAs). These long-chain PUFAs were previously thought to be absent in procaryotes, with the notable exception of a single marine Flexibacter sp. In three barophilic strains tested at 2°C, there was a general increase in the relative amount of PUFAs as pressure was increased from a low growth pressure towards the optimal growth pressure. In Vibrio marinus MP-1, a psychrophilic strain, PUFAs were found to increase as a function of decreasing temperature at constant atmospheric pressure. These results suggest the involvement of PUFAs in the maintenance of optimal membrane fluidity and function over environmentally relevant temperatures and pressures. Furthermore, since these lipids are essential nutrients for higher taxa and are found in large amounts in the lipids of deep-sea vertebrates and invertebrates, an important, specific role for deep-sea bacteria in abyssal food webs is implicated.
334 citations
TL;DR: Consideration of cell carbon, nitrogen, and protein composition suggests that the copepods are maximizing nitrogenous ingestion (total protein and/or nitrogen).
Abstract: The copepod Acartia tonsa displayed nearly two-fold higher ingestion rates on faster-growing cells of the diatom Thalassiosira weissflogii compared to ingestion rates on slower-growing cells of that species at the same cell concentration. Ingestion rates on slow-growing cells were also enhanced by the addition of cell-free aliquots of algal exudate to the experimental feeding chambers. In addition, the faster-growing algal cells were selectively ingested by the copepod when the two cell types were mixed together in different proportions, indicating that physiological differences between growing cells are a critical factor in the food detection/selection process of zooplankton. Consideration of cell carbon, nitrogen, and protein composition suggests that the copepods are maximizing nitrogenous ingestion (total protein and/or nitrogen). Selectivity for cells with higher protein content results in a higher daily protein ration, even if the selection process results in a decreased rate of ingestion in mixtures of cell types.
288 citations
TL;DR: Oceanic macroaggregates sampled from the Sargasso Sea are associated with bacterial and protozoan populations up to four orders of magnitude greater than those present in samples from the surrounding water.
Abstract: Oceanic macroaggregates (marine snow and Rhizosolenia mats) sampled from the Sargasso Sea are associated with bacterial and protozoan populations up to four orders of magnitude greater than those present in samples from the surrounding water. Filamentous, curved, and spiral bacteria constituted a higher proportion of the bacteria associated with the particles than were found among bacteria in the surrounding water. Protozoan populations were dominated numerically by heterotrophic microflagellates, but ciliates and amoebas were also observed. Macroaggregates are highly enriched heterotrophic microenvironments in the oceans and may be significant for the cycling of particulate organic matter in planktonic food chains.
259 citations
TL;DR: The diversity and abundance of protozoa in a productive freshwater pond during a 2-day period in June 1987 are consistent with the consensus opinion expressed in the marine literature that protZoa play a fundamental role in microbial food webs within aquatic ecosystems.
164 citations