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Grazing and Trophic Transfer

Grazing and Trophic Transfer. Sam Rankin BOT 437 May 21, 2009. Classic Food Web. Classic Food Web: Primary producers = phytoplankton Primary consumers = herbivorous zooplankton (eg. Copepods) Secondary consumers = carnivorous zooplankton (eg. Chaetognaths)

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Grazing and Trophic Transfer

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  1. Grazing and Trophic Transfer Sam Rankin BOT 437 May 21, 2009

  2. Classic Food Web • Classic Food Web: • Primary producers = phytoplankton • Primary consumers = herbivorous zooplankton (eg. Copepods) • Secondary consumers = carnivorous zooplankton (eg. Chaetognaths) • Tertiary consumers = jellyfish and fish • Etc • Microbial Loop • Bacteria which clean up the scraps from the food web, DOC/POM -- Bactivorous zooplankton -- Increased efficiency of food web

  3. doi:10.1038/nature04157

  4. Microzooplankton • Importance of microzooplankton (Calbet, 2008) • Dinoflagellates, ciliates, copepod nauplii, copepodites • Most primary productivity circulates within lower trophic levels and microbial loop • Little making it to higher trophic levels • Productive waters: • 60% of primary productivity consumed by micro zoo • Main grazers of diatoms and harmful algae are dinoflagellates • Other important grazers are cilates and rotifers • All provide food for copepods • Oligotrophic waters: • 75% of primary productivity consumed by microzoo • Main grazers are nanoflagellates (2-5 μm) • Inefficient grazing of chain forming diatoms by larger zooplankton? • Perhaps, but still important for pelagic food webs

  5. Transfer Efficiency • Transfer efficiency=the ratio of production at trophic level t to production at previous trophic level • In marine food webs ~0.1-0.2 • Therefore 80-90% energy loss between each level • Food chain efficiency (FCE) = proportion of total energy transferred from primary production to top trophic level • Number of trophic levels depends on the individual size of primary producers • Pelagic: small phytoplankton, long food chain resulting in small top predators • Coastal: large phytoplankton, short food chain with large top consumer

  6. Transfer Efficiency • Algal food quality also drives food chain efficiency • Dickman et al. (2008) showed that low C:N ratios of primary producers increased the FCE, while high C:N ratio lowered it • Driven by light nutrient regime • Ie. Low light/high nutrient regime favored cryptomonads FCE = 0.06 High light/low nutrient regime favored cyanobacteria FCE < 0.01

  7. Grazing of Bacteria • Heterotrophic and mixotrophic flagellates bacterial consumption in Lake Annecy, France (Domaizon et al., 2003) • Measured abundance of bacteria and flagellates, primary and bacterial production, and bacterial grazing rates by flagellates • Major taxa: Kinetoplastids, Choanoflagellates, Heterokonts, Cryptomonads, Chrysophytes, Chlorophyte • Grazing rates estimated by ingestion of fluorescent beads

  8. Grazing of Bacteria

  9. Grazing of Bacteria • High variability and seasonility of grazing rates between species • Heterotrophs: 0-30 bacteria per individual per hour • Mixotrophs: 10-55 bacteria per individual per hour • Represented 0.1-62.4% of bacterial production • Highest impact was in winter in spring, mostly by mixotrophs (Cryptomonads and Dinobryon) • Shows importance of mixotrophs in microbial loop, especially in oligotrophic waters

  10. Antarctic Lake • Study of top-down and bottom-up forces on bacteria, picoplankton, and phytoplankton in Antarctic lake (Allende, 2009) • Even linked food chain: herbivores and phytoplankton • Dominating phytoplankton are Chrysophyceae (4 species) and some Chlorophyceae • Autotrophic and mixotrophic • Microbial food web: bacteria & picoplankton • 2 microcosm experiments (in situ) • 1) three filter treatments: • 50 µm: ciliates & copepods removed • 20 µm: rotifers removed • 3 µm: algae & flagellates removed 2)same but with N & P supplement • Plus whole water control

  11. Antarctic Lake • Release of grazers for bacterioplankton and phytoplankton resulted in increase in growth rate even in low nutrient treatment • Picoplankton growth rate decreased in absence of grazers with low nutrients • Suggests that grazers may supply nutrients to picoplankton • Presence of grazers may enhance picoplankton growth

  12. References Allende, L. 2009. Combined effects of nutrients and grazers on bacterioplankton and phytoplankton abundance in an Antarctic lake with even food-chain links. Polar Biol 32:493-501. Calbet, A. 2008. The trophic roles of microzooplankton in marine systems. – ICES Journal of Marine Science, 65: 325–331. Dickman, E. M., Newell, J. M., Gonzalez, M. J., and Vanni, M. J. 2008. Light, nutrients, and food chain length contrain planktonic evergy transfer efficiency across multiple trophic levels. PNAS 105(47):18408-18412. Domaizon, I., Viboud, S., and Fontvieille, D. 2003. Taxon-specific and seasonal variations in flagellates grazing on heterotrophic bacteria in the oligotrophic Lake Annecy. FEMS Microbiology Ecology 46:317-329. Lalli, C. M., and Parsons, T. R. 1997. Energy Flow and Mineral Cycling in Biological Oceanography An Introduction. Pp. 112-146. Butterworth Heinemann, Woburn, MA.

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