How Daphnia copes with excess carbon in its food
- First Online:
- Cite this article as:
- Darchambeau, F., Faerøvig, P.J. & Hessen, D.O. Oecologia (2003) 136: 336. doi:10.1007/s00442-003-1283-7
Animals that maintain near homeostatic elemental ratios may get rid of excess ingested elements from their food in different ways. C regulation was studied in juveniles of Daphnia magna feeding on two Selenastrum capricornutum cultures contrasting in P content (400 and 80 C:P atomic ratios). Both cultures were labelled with 14C in order to measure Daphnia ingestion and assimilation rates. No significant difference in ingestion rates was observed between P-low and P-rich food, whereas the net assimilation of 14C was higher in the treatment with P-rich algae. Some Daphnia were also homogeneously labelled over 5 days on radioactive algae to estimate respiration rates and excretion rates of dissolved organic C (DOC). The respiration rate for Daphnia fed with high C:P algae (38.7% of body C day-1) was significantly higher than for those feeding on low C:P algae (25.3% of body C day-1). The DOC excretion rate was also higher when animals were fed on P-low algae (13.4% of body C day-1) than on P-rich algae (5.7% of body C day-1) . When corrected for respiratory losses, total assimilation of C did not differ significantly between treatments (around 60% of body C day-1). Judging from these experiments, D. magna can maintain its stoichiometric balance when feeding on unbalanced diets (high C:P) primarily by disposing of excess dietary C via respiration and excretion of DOC.