Phosphorus dietary assimilation and efflux in the marine copepod Acartia erythraea

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.

Multielement Stoichiometry in Aquatic Invertebrates: When Growth Dilution Matters

“…Studies that exposed organisms simultaneously to metals dissolved in water and in food or in water only also were excluded. Experimental feeding periods were generally less than the gut passage time for the animals in most studies, with a few exceptions (Fisher and Teyssie 1986;Fisher et al 1996;Chang andReinfelder 2000, 2002;Liu et al 2006).…”

Phosphorus metabolism of reef organisms with algal symbionts

“…The gain of P from POP sources may vary substantially. For macrozooplankton, 7 copepods ingested·cm −2 ·d −1 (Lewis 1992), with 0.05 μg P/prey (Liu et al 2006), bring 0.35 μg P·cm −2 ·d −1 or 0.01 μmol P·cm −2 ·d −1 . In addition, grazing rates on pico-and nanoplankton have been estimated previously to range between 0.08 and 15 μg P·cm −2 ·d −1 , or 0.002-0.4 μmol P·cm −2 ·d −1 .…”

Defining the “to” in end-to-end models

“…When confronted with food of disadvantageous composition, a consumer may compensate for (ingest or assimilate more) or exacerbate (typically by prey rejection) the impacts of dietary deficiency (Mitra and Flynn, 2005). Consumption of different prey species and/or gut evacuation rates vary in order to maintain a high growth rate (Liu et al, 2006; with prey consumption varying in linear or non-linear relationship with prey availability (Hansen et al, 1990). Such feeding behaviours impact nutrient and energy flow across trophic levels.…”

“…Many of the studies on copepods, for example, focus on short-term experiments with egg-producing females thus ignoring not only the male population but also the naupliar and juvenile stages. Further, often experiments on various zooplankton communities focus on either the quantity of available food (e.g., Liu et al, 2006) or the quality (typically defined by taxonomic differences; e.g., Jones and Flynn, 2006) of food. However, in nature, changes in quality and quantity synergistically affect community dynamics, in some instances resulting in mass extinction events (fish kills caused by harmful algal bloom events; Kempton et al, 2002).…”