Parasites as Pollution Indicators in Marine Ecosystems: a Proposed Early Warning System

There are good reasons for focusing on parasites in the search for indicators to monitor the effects of pollutants on marine organisms. Firstly, there are more parasitic than free-living species. Secondly, in parasites with complex life cycles, the different stages have widely differing requirements, so that each stage must be assessed separately, thereby greatly increasing the number of potential indicators. Thirdly, many parasites have delicate free-living transmission stages which are highly sensitive to environmental change. A reduction in their levels of infection will serve as an early warning that changes are occurring. Conversely, other parasites are highly resistant to environmental change and will respond by increased levels of infection. As a general rule, infections with endoparasitic helminths tend to decrease, while infections with ectoparasites tend to increase, with increasing levels of pollution.