Common starfish can act as a bioindicator for heavy metal pollution
Context of the study
Sørford, in the Southwest of Norway, is an extremely polluted area, cadmium (Cd), mercury (Hg), and lead (Pb) reach dangerously high levels in fish and mussels. This is due to a zinc (Zn) plant and other smelters which discharged large quantities of these metals into the fjord for more than 65 years. Discharges were drastically reduced since 1986. Due to these and other measures, a gradient was established with high concentrations of heavy metals at the inner part of the fjord and low concentrations close to the opening to the sea. However, non of the organisms in which the concentrations of heavy metals were measured (cod and mussels) displayed this gradient. Therefore they can't serve as bioindicators. It's important to have an organism that can serve as a bioindicator to monitor the efficiency of the taken measures.
Content of the study
This study investigated whether the common starfish can serve as a bioindicator for heavy metal contamination. It was assessed whether the body concentrations in the starfish follow changes in the environmental concentrations (in the sediment and or water). The study examined cadmium, lead and zinc concentrations in the starfish. The concentrations of all three heavy metals were measured in three different body parts: the skeleton, the body wall and the pyloric caeca (a body part between its stomach and its gut).
Main results of the study
The concentrations were highest at the inner fjord for all 3 contaminants. This was most clear in the skeleton of the starfish, which give an indication for long term pollution (Cd: 15 µg/g, Pb: 150 µg/g, Zn: 325 µg/g; in µg metal/g dry weight). The skeleton concentrations also showed a clear decrease from the inner fjord (high) towards the sea (low) for all contaminants. The concentrations in the body wall showed this trend as well, but to a lesser extent. The concentrations in the pyloric cloaca decreased towards the sea for cadmium and lead, but not for zinc. Interestingly, in contrast to zinc and cadmium, lead tended to accumulate in the skeleton and body wall with increasing starfish size. This shows that the starfish can excrete zinc and cadmium much easier than lead.
The study concluded that the common starfish could be used as a bioindicator. The pyloric caeca can be used to investigate short term changes (days) while the skeleton can be used as an indicator for long term changes. It concluded also that the bioavailability of metals has decreased, but still might be high enough to induce sublethal toxic effects in starfish.