Evaluation of environmental deterioration by analysing fish parasite biodiversity and community structure.

The degree of biological diversity is often used as an indicator of the well-being of ecological systems. This approach can also be applied to analyse biodiversity in parasite communities. In particular, studies on parasite communities can be employed to detect a decline in biodiversity which characterizes habitats affected by pollution. Beside the most widely used diversity indices, such as the Shannon, Brillouin and inverse Simpson, that have been widely applied in different host-parasite systems, new approaches have been recently developed in order to overcome problems related to high dominance. Walther et al. (1995) proposed an asymptotic equation suitable for evaluating parasite species richness as a function of sampling effort. Such an equation was earlier proposed by Miller and Weigert (1989) to describe plant species diversity and to calculate true species richness as the ratio between the increase in species richness (a) and the parameter that set the species richness asymptote (b). True species richness has been shown to decline in parasite communities of mugilids collected in polluted areas. Biodiversity calculations can also be run in parallel with other biological studies for the description of environmental conditions. The completion of parasite life cycles requires complex biocoenotic interactions and is restricted by environmental constraints. Therefore another approach for monitoring the health of an ecosystem was by analysing the ratio between monoxenous and heteroxenous parasite species infecting model hosts. By this methodology it was possible to confirm pollution effect highlighted by other quantitative methods.