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

Foraminifera are unicellular organisms which are important for marine C and N processing. 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 therefore contaminated by heavy metals from shipping in the past, this study examined the effect of heavy metal pollution on the food uptake of the most common foraminiferal species of the Baltic Sea, Elphidium excavatum. In 2019, we collected water and sediment containing living E. excavatum in the Kiel Fjord. In laboratory experiments, Baltic Sea seawater was enriched with metals at various levels above normal seawater: Zn (9.2-, 144- and 1044-fold), Pb (2.4-, 48.5- and 557-fold) and Cu (5.6- and 24.3-fold), and the foraminiferal uptake of 13C- and 15N-labelled phytodetritus was measured by isotope ratio mass spectrometry. Significant differences in food uptake were observable at different types and levels of heavy metals in sea water. An increase in the Pb concentration did not affect food uptake, whereas strong negative effects were found for high levels of Zn and especially for Cu. Interestingly, experiments with short incubation periods (1 and 5 days) showed greater differences in food uptake from undisturbed conditions than those of longer incubation times (10 and 15 days). In summary, an increase in the heavy metal pollution in the Kiel Fjord will likely lead to a significant reduction in the turnover of organic matter by foraminifera such as E. excavatum.