MEPS 218:239-248 (2001)  -  doi:10.3354/meps218239

Comparative assimilation of Cd, Cr, Se, and Zn by the barnacle Elminius modestus from phytoplankton and zooplankton diets

Philip S. Rainbow1,*, Wen-Xiong Wang2

1Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom
2Department of Biology, The Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong, PR China

ABSTRACT: Assimilation from the diet is established as a key factor in the accumulation of very high trace metal concentrations by the barnacle Elminius modestus. Assimilation efficiencies (AE) of Cd, Cr, Se and Zn were measured from a diet of different phytoplankton (2 diatoms, a dinoflagellate, a prasinophyte and a chlorophyte) and of zooplankton (the copepod Acartia spinicauda with metal accumulated from solution or diet). AEs of Cd, Se and Zn (but not Cr) varied greatly with phytoplankton type, and for Cd and Se the AE was correlated with the percentage of metal burden held in the cytoplasm of the phytoplankton diet. AE was generally higher from the zooplankton diet than from a phytoplankton diet. Variation in AEs of Cd, Se and Zn was not explained by any correlation with the percentage of copepod metal burden held in the soft tissues, nor was there variation for either Cd or Zn according to whether the copepod prey had accumulated metal from dissolved or food sources. Comparisons of the assimilation and efflux of accumulated metals by the archaeobalanid barnacle E. modestus and literature data for (phylogenetically younger) balanid species of the genus Balanus indicate some differences in digestive physiology of barnacles from the 2 families, tending towards higher AEs in the balanids. Modeling of the accumulation of Cd and Zn by E. modestus predicts that for each metal >97% of accumulated metal has been derived from dietary ingestion. The dominance of dietary ingestion in trace metal accumulation is a function of the conspicuously high assimilation efficiencies and high ingestion activity of barnacles. This study adds to the small but growing list of examples highlighting the significance of trophic transfer in metal accumulation by aquatic invertebrates.

KEY WORDS: Barnacles · Elminius modestus · Dietary uptake · Assimilation · Cadmium · Chromium · Selenium · Zinc

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