MEPS 321:193-202 (2006)  -  doi:10.3354/meps321193

ABSTRACT: We examined the metabolism of phosphorus (P), including its dietary assimilation, efflux, and regeneration, in the marine subtropical copepod Acartia erythraea feeding on diverse types of marine phytoplankton. The P assimilation efficiency (AE) ranged between 19 and 78% when the copepods were fed 6 algal diets at the same concentration (1.45 mg C l^–1). Among the different algal diets, the AEs were not significantly related to the ingestion rate and the food gut passage time of copepods, or the P partitioning in the algal cytoplasm. The P AE decreased ca. 2-fold when the food concentration increased from 0.073 to 3.625 mg C l^–1, but was not influenced by the P quota in diatoms. The P efflux rates in the copepods feeding on diatoms were 0.30 to 0.36 d^–1 over the food concentrations examined; the efflux rate was significantly higher when the copepods ingested diatoms with higher P quotas, suggesting that the P homeostasis in the copepods may possibly be achieved by efflux of P from the body. During the dietary assimilation and efflux periods, most P lost from the copepods was regenerated into the dissolved phase and only a small portion of P was detected in other compartments (mainly in the feces), suggesting that copepods rapidly regenerate particulate P into the surrounding waters. Our study indicated that both P dietary assimilation and efflux can play an important role in maintaining the P stoichiometry in copepods.

KEY WORDS: Phosphorus · ³³P · Copepods · Assimilation · Efflux · South China Sea