On the distribution and abundance of eel parasites in Nova Scotia: influence of pH.

The geographic distribution of metazoan parasites of American eels (Anguilla rostrata) was determined from 28 sites in the Southern Upland and adjacent regions of Nova Scotia. Twelve parasite species were encountered. Component community diversity as measured by species richness, Shannon-Wiener index (H') and Hill's number (N1) decreased when pH < 5.4. Seven species (Azygia longa, Crepidostomum brevivitellum, Bothriocephalus claviceps, Proteocephalus macrocephalus, Paraquimperia tenerrima, Echinorhynchus salmonis, Ergasilus celestis) were found in both the Southern Upland and adjacent watersheds to the north. Three species (Pseudodactylogyrus anguillae, Diplostomum sp., Pomphorhynchus bulbocolli) were found only at sites beyond the Southern Upland, which flowed into the Bay of Fundy and had high pH values ( > 5.4). Two species (Daniconema anguillae, Echinorhynchus lateralis) were limited to sites within the Southern Upland. Digeneans were absent from rivers in the southwest with pH values < 4.7. Variation in occurrence of parasite species was observed among rivers within a single watershed and among years within individual sites. Nevertheless, the impact of acidity at the local level was observed regionally across the Southern Upland of Nova Scotia. These data support the hypothesis that parasite assemblages may be good indicators of environmental stress.