Does Eutrophication Enhance Cd Bioavailability by Trophic Transfer to the Marine Amphipod Leptocheirus Plumulosus from Microalgae?
Bioavailability and nutrient effects on the trophic transfer of Cadmium (Cd) associated with microalgae to the marine amphipod, Leptocheirus plumulosus, were investigated. Cd assimilation efficiencies (AE) were measured by a pulse-chase technique using a radiotracer. Cd AE in L. plumulosus significantly varied among algal species tested, and was highest (38.8 %) for the benthic diatom Nitzschia punctata, lowest (5.9%) for the planktonic diatom Thalassiosira weissflogii, and intermediate (15.6%) for the planktonic dinoflagellate Isochrysis galbana. Instantaneous egestion rates of Cd displayed a typical biphasic pattern over 96 h of depuration. Depuration in seawater-only of L. plumulosus yielded the highest Cd AE of 35.0%, whereas AEs in which depuration occurred in natural sediment and processed sediment were only 5.3% and 4.3%, respectively. Body size, ranging from 0.5 to 2.0 mm, of L. plumulosus feeding on labeled T. weissflogii did not affect Cd AEs.
Nitrate enrichment from 0-180 uM on algae significantly increased Cd AEs by L. plumulosus from 9.4-18.8% for T. weissflogii, from 10.0-27.3% for N. punctata, and from 10.0-16.2% for I. galbana. Physiological turnover (elimination) rate constants of Cd in L. plumulosus ranged from 0.016-0.025 h-1 for the three algal species, and were independent of nitrate addition. Algal fractionation revealed that nitrate enrichment strongly enhanced the fraction of Cd associated with cytoplasm, which probably contributed to the increased Cd AEs by L. plumulosus.
Phosphate addition (0 - 7.5 uM) on algae showed that Cd AEs of L. plumulosus were from 26.4-35.8% for T. weissflogii, and from 15.3-18.5% for N. punctata. Phosphate enrichment did not significantly affect trophic transfer of Cd from algae to L. plumulosus. Cd fractionation in cytoplasm showed no obvious correlation with phosphate addition.
Overall, there was a significant linear relationship between the Cd AE of L. plumulosus and the distribution of Cd within algal cells. My work suggests that eutrophication by nitrate enrichment, but not phosphate, has the potential to enhance the trophic transfer of metals from pelagic and benthic microalgae to grazers in coastal benthic food webs.
Advisor:Ralph J. Portier; Kevin R. Carman; John W. Fleeger
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:11/04/2004