Effects of heavy elements (Pb, Cu, Zn) on algal food uptake by Elphidium excavatum (Foraminifera)

Foraminifera are unicellular organisms and play a pivotal role in the marine material cycles. Past observations have shown that the species Elphidium excavatum is the most common foraminifera in the Baltic Sea. Feeding experiments showed that the food uptake and thus the turnover of organic matter are influenced by changes of physical parameters (e.g., temperature, salinity). Since many areas of the Baltic Sea are strongly affected by anthropogenic activity and are strongly contaminated by heavy elements from shipping in the past, this study examined the effect of heavy elements pollution on the food uptake of the most common foraminiferal species of the Baltic Sea, E. excavatum which was a subject of several previous studies. Therefore, Baltic Sea seawater was enriched with metals at various levels above normal seawater levels and the uptake of ¹³C- and ¹⁵N-labelled phytodetritus was measured by isotope ratio mass spectrometry. For each combination of metal type, concentration and time point 20 individuals of E. excavatum (three replicates) were fed with the green algae Dunaliella tertiolecta. The effect of dose parameters was measured in a two-way analysis of variance. Significant differences of food uptake were observable at different types and levels of heavy elements in sea water. Even a 557-fold increase in the Pb concentration did not affect food uptake, whereas strong negative effects were found for higher levels of Zn (144 and 1044-fold) and especially for Cu (5.6 and 24.3-fold). In summary it can be stated, that an increase in the heavy elements pollution in the Kiel Fjord will lead to a significant reduction in the turnover of organic matter by foraminifera such as E. excavatum.