| dc.description | American eels, Anguilla rostrata, were collected (via electrofisher and trap pots) from May to October, during 1995 and 1996, from 8 sample sites within a watershed (of varying pH and flow regime) in southwestern Nova Scotia. Aspects of eel biology and their metazoan parasites were examined to study: (i) the influence of host biology and season on the distribution of parasite fauna; (ii) the spatiotemporal dynamics of parasite component communities within the catchment; (iii) applicability of using several parasites as 'biological tags' (indicators) of eel riverine dispersal and (iv) developmental processes influencing both infra- and component community structure. During their first two years in freshwater, eels (6 to 10 cm) are free of metazoan parasites and disperse widely throughout the watershed. In their third year in freshwater, eels (10 to 13 cm) commence localized residency and begin to acquire metazoan parasites. Results of a two-year mark-recapture study demonstrated that 'yellow' eels ($>$16 cm) are site specific with restricted home ranges. Eleven species of parasites were found within the watershed, six of which were host-specific to eels, while 5 were generalists (found as adults in a variety of fish species). Species richness and size of the parasite population of the intestinal helminth infracommunity increased with eel length, but for the majority of eels ($\sim$95%), the richness did not exceed 4 species. The majority of intestinal helminth infracommunities were dominated by eel specialists. The helminth community composition appeared to be most influenced by eel diet. Site to site variation among the intestinal helminth component communities was maintained by localized eel residency. Helminth component communities at sites of low pH ($\sim$4.3-5.2) were characterized by low species richness, low diversity and high dominance while opposite patterns were observed at sites of high pH ($\sim$5.5-6.8). The patterns observed among intestinal helminth component communities and pH parallelled those of free-living benthic macroinvertebrate assemblages at the same sites. Correspondence ordination further emphasized the linkage between parasite abundance and macroinvertebrate 'source' hosts with respect to pH. Consistency of annual patterns and predictability was attributed to the high proportion of specialists--thus implying the existence of a strong phylogenetic component in helminth community structure. From July to October, the seaward downstream migration of sexually maturing 'silver' eels could be plotted using changes in component community structure along the watershed. Parasites whose occurrence (and abundance) was influenced either by pH, stream flow or eel size, have good potential to be used as biological tags--indicators of eel riverine dispersal or habitat pH. It was concluded that ontogenetic (ultimate processes) influences (e.g. host biology, diet selectivity) were most important, as structuring processes, at the infracommunity level; but local habitat (proximate processes) was the most influential structuring process at the component community level. Furthermore, both processes (local and regional) were not mutually exclusive and it appeared phylogeny set the template potential parasite species richness) but local ecological factors determined composition and abundance. | en_US |
