Journal of Plankton Research, Vol 21, 1753-1764, Copyright © 1999 by Oxford University Press
M Schmidt, Y Zhang and D Hutchins
Previous studies have demonstrated that growth of marine phytoplankton,
bacteria and protozoa can be limited by the availability of Fe. We report
evidence that the amount of Fe assimilated by crustacean grazers is
affected by the Fe status of their pry. 59Fe and
14C radiotracers were used to follow the fate of Fe
and carbon during trophic transfer from diatoms to copepods. Fe
assimilation efficiency was higher for copepods ingesting Fe-limited
Thalassiosira weissflogii (17%) compared to diatoms
that were not limited by Fe (10%), but assimilated Fe was lost more rapidly
by copepods ingesting Fe-limited prey. Fe:C assimilation ratios were lower
in copepods (5-12
ORIGINAL ARTICLES
Assimilation of Fe and carbon by marine copepods from Fe-limited and Fe-replete diatom prey
College of Marine studies, University of Delaware, 700 Pilottown Road, Lewes DE 19958, USA; Corresponding author
mol Fe:mol C) than the
cellular ratios of the phytoplankton prey (17-35
mol Fe:mol C),
suggesting that copepods do not accumulate Fe relative to C during grazing.
The largest single fate for Fe and C after grazing was regeneration to
dissolved pools. Fe:C ratios in dissolved pools were approximately equal to
the ratios in the original prey, but Fe:C ratios were higher in particular
pools (largely fecal pellets), which should facilitate the export of Fe
from the euphotic zone relative to C. Although copepod grazing does recycle
cellular Fe and C, our results indicate that grazing may also tend to
enhance Fe stress for lower trophic levels by removing Fe from the euphotic
zone faster than C.
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