Implications of climate change for parasitism of animals in the aquatic environment

Climate change can occur over evolutionary and ecological time scales as a result of natural and anthropogenic causes. Considerable attention has been focused in recent years on the biological consequences of global warming. However, aside from studies on those deleterious parasites that cause disease in man, little effort has been dedicated to understanding the potential changes in the parasite fauna of animal populations, especially those in aquatic systems. Predictions using General Circulation Models, among others, are examined in terms of their consequences for parasite populations in freshwater and marine ecosystems, concentrating on the temperate and boreal regions of eastern North America. Biological effects due to global warming are not predictable simply in terms of temperature response. It is also essential to explore the effects on aquatic parasites of alterations in host distribution, water levels, eutrophication, stratification, ice cover, acidification, oceanic currents, ultraviolet-light penetration, weather extremes, and human interference. Evaluation of the potential response of parasites of aquatic organisms to climate change illustrates the complexity of host-parasite systems and the difficulty of making accurate predictions for biological systems. Parasites in aquatic systems will respond directly to changes in temperature but also indirectly to changes in other abiotic parameters that are mediated indirectly through changes in the distribution and abundance of their hosts. Local extirpations and introductions may be expected as a result. In the long term, climatic change may influence selection of different life-history traits, affecting parasite transmission and, potentially, virulence.