Grazing and Trophic Transfer

Sam RankinBOT 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)– 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

doi:10.1038/nature04157

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

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

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

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

Grazing of Bacteria

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

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

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

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.