Effet de l'apport de fer et sa relation avec un chélateur (EDTA) sur la croissance et la composition minérale des algues (Platimonas suecica) et des rotifères (Brachionus plicatilis)

Abstract

In order to study the incorporation of trace elements into a trophic chain, the effects of the variations in the composition of trace minerals (Fe, Zn, Cu, Mn) of the algal culture medium are followed in an artificial food chain consisting of the unicellular alga Platymonas suecica and the rotifer Branchionus plicatilis cultivated in bloom. A high level of chelating agent decreases the production of algae and rotifers, it depresses the absorption of trace minerals into algae, but this effect is clearly reflected in the 2nd level of the food chain (in rotifers) only as far as zinc is concerned. An optimum growth of P.suecica is obtained when the medium contains 267 kg/l of Fe and 4,97mg/l of EDTA. This medium gives also the best growth of rotifers. In the algae, iron absorption is directly correlated with its concentration in the medium. The absorption of other minerals (Zn, Cu, Mn) is not dependent on iron concentrations. However the trace mineral contents of rotifers are (i.e. at the second step of the food chain) influenced by the iron levels in algal culture: high Fe concentrations increase its absorption and decrease that of zinc, copper and manganese. Therefore the interactions between iron and other minerals are not similar in rotifers and algae