Effects of the environment, the host and biotic interactions on the gill parasite assemblages of Fundulus heteroclitus in central Chesapeake Bay

I studied the effects of season, locality of the host population, host sex and length, and biotic interactions on the prevalences and densities of gill parasites of mummichogs (Fundulus heteroclitus) collected from two creeks (n = 242) differing in salinity in central Chesapeake Bay (August 1991 to June 1992). Ten parasite taxa were found: mobile peritrichs (Trichodinidae) (prevalence range: 12-88%); sessile peritrichs (0-50%) (Ciliophora); Myxobolus funduli (58-94%) (Myxozoa); Gyrodactylidae (Gyrodactylus sp. and Fundulotrema sp.) (0-94%) and Salsuginus sp. (74-100%) (Monogenea); metacercaria of Phagicola diminuta (75-100%) and Echinochasmus schwartzi (79-100%) (Digenea); Ergasilus manicatus (25-100%) (Copepoda); Lironeca ovalis (0-11%) (Isopoda); and cysts of unknown etiology (CUEs) (64-94%) (unknown taxon). Densities of Myxobolus funduli, E. schwartzi and E. manicatus peaked during spring, Gyrodactylidae in winter, and CUEs in fall. Densities of M. funduli, Salsuginus sp., P. diminuta, E. schwartzi, and E. manicatus (in at least one season) were significantly higher in Indian than in Brooks Creek. Host sex did not affect parasite densities, except in one sample; densities of P. diminuta and E. schwartzi increased with host length for females only. CUE density was positively correlated with host length; there were weaker positive correlations of gyrodactylid and Salsuginus sp. densities with host length.; A high potential for biotic interactions among the parasites was suggested by the presence of five core species (at least 60% prevalence), high population densities of some taxa, and the fact that most fish were multiply infected with four to eight parasite taxa per fish. Multiple regressions were used to determine whether parasite densities (independent variables) affected niche breadths or mean positions (dependent variables) of parasites in three dimensions of the gill habitat. The niche breadth of each species increased primarily in response to increases in its own population density. However, in one dimension, niche breadths of Salsuginus sp. and E. manicatus were independent of intraspecific density, and the niche breadth of E. schwartzi increased with increases in the density of P. diminuta. Mean positions of most parasites were not affected by densities of co-occurring taxa.