”But when the crustaceans were exposed to both polluted sediment and low oxygen levels at the same time, their defence was not enough to protect them from damage on important structures in the cell, such as DNA and lipids”, explains Marie Löf, author of a recently published PhD thesis from the Department of Applied Environmental Science (ITM) at Stockholm University.

”This is a discouraging result given the environmental situation in the Baltic Sea”, says Marie Löf. Dead bottoms with too little oxygen to support higher life than bacteria cover a large part of the Baltic Sea and pollution levels are still high, despite efforts to reduce pollution from point sources. The Baltic Sea is like a bathtub with a water exchange only every 30 years, thus everything that enters the sea remains there for a long time and affects the ecosystem.

Embryo damage linked to different contaminants

These small crustaceans are an important species in the species poor, brackish water environment of the Baltic Sea, and their reproduction is used as bioindicators of contaminant exposure in the Swedish marine environmental monitoring. In this PhD thesis concentrations of contaminants in the sediment were also analysed from several sites in the northern Baltic Sea, the Gulf of Bothnia.

”For the first time we have been able to show that different types of embryo damage in Monoporeia affinis can be linked to different contaminants that we analysed in the sediment”, says Marie Löf. Malformed embryos were linked to increased concentrations of the heavy metal cadmium and PCBs, while other types of embryo damage was found in sediment with high concentrations of PAHs and other heavy metals.

Bad news for the Baltic Sea 

”We found that the defence system that was activated in the experiments in polluted sediment and oxygen deficiency, also was activated in crustaceans from the Gulf of Bothnia that showed high numbers of damaged embryos. These are interesting results that might increase our understanding of the effects of exposure to multiple contaminants and other stress factors such as oxygen deficiency”, says Marie Löf. These little crustaceans show us that they are stressed by contaminants in the sediment and by low oxygen levels and that their numbers in some areas likely will decline due to these facts. ”In the bigger picture, for the Baltic Sea, this is bad news. If one important species declines there is not another that can take its place in the food web. We need to be more careful with the Baltic Sea because it is such a vulnerable ecosystem from many points of views”, concludes Marie Löf.