Effect of food quality on carbon and nitrogen growth efficiency in the copepod Acartia tonsa

Abstract

Populations of the copepod Acartia tonsa were fed a mixture of algal prey (diatom Thalassiosira weissflogii, prymnesiophyte Emiliania huxleyi, dinoflagellate Aureodinium [Gymnodium] pigmentosum) supplied at saturating concentrations, grown under either nitrogen-sufficient or nitrogen-deplete conditions, in order to study the impact of food quality on production and development throughout the life cycle of the copepod. Changes in predator population structure and biomass were recorded, along with consumption of each of the algal groups, permitting C and N growth efficiencies to be estimated. There was a clear difference in the Acartia tonsa population structure when fed N-sufficient or N-deplete prey, with those fed N-deplete prey slower to develop and reproduce and laying fewer eggs. Algal nutrient status affected selectivity between the diatom and dinoflagellate, the latter being favoured under nutrient-deplete conditions, perhaps in part because their C:N ratio was less susceptible to altered nutrient status. There was no clear difference in the N growth efficiency (N-GE, typically 5%) between N-sufficient and N-deplete prey, but certainly efficiency did not increase with N-deplete prey. C growth efficiency (C-GE) declined from 5 to 2% with N-deplete prey. However, while the ratio of N-GE:C-GE was clearly different between N-sufficient (1) and N-deplete (2.5) treatments, actual growth efficiencies increased with time during the progression to later life history stages, culminating in highest efficiencies during active egg production. Caution should be exercised in assigning GE and predation rates in models incorporating zooplankton feeding on prey of variable nutrient status; these parameters are not constants and GE estimates from egg production experiments are likely to significantly overestimate efficiencies over the whole copepod life cycle.

Phytoplankton growth allometry and size- dependent C:N stoichiometry revealed by a variable quota model

“…If future climate change scenarios select for smaller cells due to increased stratification, and reduced nutrient supply (Daufresne et al 2009, Finkel et al 2010), the C:N of the phytoplankton community will increase, and the extent of the increase will be determined by the size structure of the phytoplankton community. C:N of phytoplankton biomass has been suggested to affect assimilation efficiency of zooplankton grazers (Jones et al 2002, Jones & Flynn 2005, and thus export through fast-sinking zooplankton fecal pellets. Therefore, phytoplankton size structure, along with their sizedependent C:N ratio, affects trophic interaction between autotrophs and heterotrophs and export of organic carbon.…”

“…Consequently, phytoplankton C:N stoichiometry may be size dependent. The C:N stoichiometry of phytoplankton cells has important consequences for estimating the new production of C based on nutrient supply, the nutritional value of phytoplankton cells for their grazers (Jones et al 2002, Jones & Flynn 2005, and thus the food web structure, the remineralization of particles and the dissolved inorganic carbon to nutrient ratio in deep water. Future climate change may alter the size structure of phytoplankton communities in the surface ocean; however, there is a lack of understanding about how the C:N stoichiometry of phytoplankton is linked to cell size (Allen & Gillooly 2009).…”

Feeding and reproduction in a small calanoid copepod: Acartia clausi can compensate quality with quantity

“…Production was calculated by converting EPR to carbon units following Kiørboe & Sabatini (1995). We also estimated the population growth efficiency (PGE, µg viable egg C µg C ingested -1 ) according to Jones et al (2002).…”

Can copepods be limited by the iron content of their food?

“…In freshwater ecosystems, low concentrations of phosphorus in the food of Daphnia reduce P excretion, final body mass, reproductive rate, clutch size, and growth rate, while increasing mortality rate (Sterner et al 1993;Sterner and Hessen 1994;Elser et al 2001). Likewise, marine copepods fed a variety of algal prey with low cellular nitrogen : C ratios grow and develop slower, and produce fewer eggs (Jones et al 2002). Low N diatom food can also result in increased production of resting eggs by Acartia tonsa (Augustin and Boersma 2006).…”