A stoichiometric analysis of the zooplankton–phytoplankton interaction in marine and freshwater ecosystems

Phytoplankton taxonomic variability in nutrient utilization and primary production in the Ross Sea

“…Although grazing pressure appeared to be low during our study (on the basis of low concentrations of chlorophyll breakdown products), zooplankton can have an appreciable influence on mineral recycling in many aquatic systems. This is because the mean N:P ratio for marine macrozooplankton (e.g., copepods) is -27 [Elser and Hassett, 1994], 68% higher than the Redfield N:P ratio for typical marine phytoplankton of 16. Because phytoplankton are richer in P than many macrozooplankton require and because macrozooplankton regulate their N:P composition at constant ratios [Andersen and Hessen, 1991], zooplankton retain N and recycle P.…”

“…Therefore grazing on diatoms by large zooplankton could explain the low C:P and N:P disappearance ratios observed during our study only if their C:P and N:P ratios were much lower than that of their diatom food source. While very low N:P ratios have been reported for zooplankton in aquatic ecosystems [Elser and Hassett, 1994 ]. ROAVERRS NBP96-6 data imply that these models currently overestimate CO2 drawdown wherever the spring phytoplankton bloom in the Southern Ocean is dominated by diatoms [Arrigo et al, 1999], which have a TDIC:PO 4 disappearance ratio -50% of the C:P ratio used by these models.…”

How Daphnia copes with excess carbon in its food

“…In systems with temporal algal limitation by P, the expected increases in respiration and DOC excretion by herbivorous zooplankton could probably increase CO 2 output to the atmosphere, decrease zooplanktivorous fish production and favour the planktonic microbial loop. Since mineral limitation also seems to be a general phenomenon in marine and particularly terrestrial ecosystems (Elser and Hassett 1994;Elser et al 2000), these regulation processes may potentially have great impacts on fluxes of C both on ecosystem and global scales. …”

“…In daphniids, which commonly are the most important grazers in lakes, P requirement for somatic growth is high whereas freshwater algae are frequently P deficient (Hessen 1992;Sterner 1993). Phytoplankton in lakes often show very high C:P ratios in comparison with consumer C:P ratios (Elser and Hassett 1994) and this could lead to P limitation of daphniid growth and lower food chain production (Sterner and Hessen 1994;Hessen 1997;Sterner et al 1998;Hessen and Faafeng 2000). Two parallel physiological adaptations which may be used by animals to cope with this excess dietary C have been suggested: (1) improvement of the assimilation of the limiting element, and (2) reduced intake, storage or disposal of the element in excess.…”

Ocean stoichiometry, global carbon, and climate

“…Reasons for this constraint have been discussed and debated over the years (e.g., refs. 6 and 7) and relative to autotrophs on land or in lakes, marine plankton do exhibit much more constrained C:N:P composition (8). In Redfield's time observations of marine C:N:P were scarce, and perhaps because theoretical emphasis was on lack of variation, additional data-especially of particulate P-were slow to accumulate.…”