Interspecific differences in the bioconcentration of selenite by phytoplankton and their ecological implications

The concentration of Se in algal cells is a primary determinant of Se tissu e contents in higher level consumers. Differences in the ability of algal s pecies to concentrate selenite and variability in ambient selenite concentr ations may be important determinants of algal Se contents. We compared upta ke of Se-75-labeled selenite by 14 algal species at 2 environmentally relev ant selenite concentrations. Se content per unit cell volume (Se/V-c) varie d by almost 4 orders of magnitude when algae were exposed to 4.5 nM selenit e and almost 5 orders of magnitude when exposed to 0.15 nM selenite. Chloro phytes typically exhibited the lowest Se enrichments, while prymnesiophytes , prasinophytes and dinoflagellates exhibited the highest. The Se/V-c of di atoms and cryptophytes varied by >2 orders of magnitude. Even at the lowest selenite concentration, about half the species concentrated Se to an exten t that might cause toxicity at higher trophic levels. Within species, the S e cell concentration typically varied by only 2- to 3-fold when exposed to selenite concentrations that differed by 30-fold. The Se cell concentration of only 1 species, the diatom Skeletonema costatum, varied in proportion t o ambient selenite concentrations. A more detailed study of the dependence between Se cell concentration on ambient selenite concentrations in the dia tom Thalassiosira pseudonana revealed an asymptotic approach to a maximum S e cell concentration at high ambient selenite concentrations (>0.1 nM). Giv en the results for other species exposed to 4.5 and 0.15 nM selenite, such saturation is likely to be a common feature. Our results indicate that the composition of the phytoplankton community could have a pronounced impact o n Se concentrations in marine food webs.