Accumulation of trace elements in a marine copepod

Abstract

We measured assimilation efficiencies (AEs) from ingested algal food, uptake rates from the dissolved phase, and efflux rate constants of five trace elements (Ag, Cd, Co, Se and Zn) in the marine copepod Temora longicornis.AEs of Ag, Cd, Co, Se, and Zn from two diatom diets were 13, 35, 14, 59, and 61%, respectively. AEs of metals from ingested natural seston collected during the spring phytoplankton bloom in Long Island Sound were comparable to AEs from diatoms. The assimilation of all trace elements within the T. Zongicornis gut took longer (4-15 h) than the gut passage time of ingested food particles. The rate constant of metal uptake from the dissolved phase was highest for Ag, followed by Zn > Cd > Co > Se. Efflux rate constants for all trace elements ranged from 0.08 to 0.30 d-l, indicating that metals were regenerated at a very fast rate in these animals. Generally, the efflux rate of metals was higher following uptake from food than uptake from the dissolved phase. The retention half-times of trace elements in copepod carcasses were 0.6-3.3 d. A bioenergetic-based kinetic model was used to quantify the relative importance of metal uptake in copepods from different pathways. The model indicates that under conditions typically encountered by copepods in nature, >50% of Zn and >98% of Se in copepods are obtained from ingested food. For Ag, Cd, and Co, >50% accumulates from the dissolved phase. The relative importance of trace element uptake from the dissolved phase vs. particulate ingestion in the overall metal uptake depends greatly on the metal AE, the feeding rate of copepods, and the partition coefficient of metals in ingested food particles.The biogeochemical cycling of trace elements in marine systems is influenced by their interactions with plankton and their transfer up the food chain. When phytoplankton are ingested by zooplankton, any unassimilated trace elements are rapidly packaged into fecal pellets and transported out of surface waters (Fowler and Knauer 1986). The release rates of metals from decomposing fecal material have been quantified for a variety of conditions and can affect the rates of metal remineralization during their descent in the water column (Lee andFisher 1992, 1994;Reinfelder et al. 1993; Wang et al. 19966). Regeneration of assimilated trace elements by zooplankton grazing can significantly affect their geochemical cycling and residence times and can affect their bioavailability to phytoplankton (Hutchins and Bruland 1994;Lee and Fisher 1994;Twiss and Campbell 1995;Twiss et al. 1996; Wang et al. 19966). However, mechanistic and quantitative studies of zooplankton regeneration have been limited. In several studies, radiolabeled phytoplankton were introduced into natural assemblages of zooplankton and other phytoplankton. Significant amounts of radioactivity were subsequently detected in the dissolved phase and in previously unlabeled phytoplankton and zooplankton assemblages. From these experimental studies it is still not known whether regeneration was due to excret...

Uptake and loss kinetics of Cd, Cr and Zn in the bivalves Potamocorbula amurensis and Macoma balthica:effects of size and salinity

“…These values are within the ranges determined for other bivalves (Mytilus edubs, Mercenaria rnercenaria, and Crassostrea viryinlca) , Reinfelder et al 1997. However, the rate constants of loss froin the bivalves in this and other studies are considerably lower than the values (0.07 to 0.3 d-') reported for crustacean zooplankton (Wang & Fisher 1998).…”

Accumulation of heavy metals in food web components across a gradient of lakes

“…This may explain the positive enrichment (BMF Ͼ 1.0) of Hg, Zn, and Cd we find in zooplankton. Wang and Fisher (1998) also found that the assimilation efficiency of Zn by marine copepods from phytoplankton was the highest relative to Cd, Co, and Se, and Ͼ50% of Zn was from ingested food. Efficient assimilation of Zn by zooplankton may help explain Zn biomagnification in zooplankton and fish in this study.…”

The trace metal composition of size‐fractionated plankton in the South China Sea: Biotic versus abiotic sources

“…Given the relatively similar biomass dry weight among the three size fractions (Table 1), the much higher surface area : volume ratios in the smaller plankton may also explain the observation of the smaller the plankton, the higher the metal quotas. Since the smaller phytoplankton would be grazed by zooplankton, part of the metals on the phytoplankton would be digested and absorbed and part of them would be repacked into fecal pellets before being transported into deep waters as sinking particles (Wang and Fisher 1998). Determining how the abiogenic particles on the phytoplankton are recycled in the deep waters, after being grazed and repackaged to fecal pellets through grazer's gastrointestinal environment, is important for illustrating the whole picture of the internal cycling of the trace metals in oceanic water columns.…”