Investigating the epibiotic peritrich Zoothamnium intermedium Precht, 1935: Seasonality and distribution of its relationships with copepods in Chesapeake Bay (USA).

Zoothamnium intermedium is an obligate epibiont ciliate and has been found in a diverse array of hosts and environments. Different studies have reported conflicting distribution patterns and host preferences, even though studies in Chesapeake Bay have suggested that the ciliate has a strong host specificity for two calanoid copepod species. We examined the life cycle, host preferences, and ecological conditions conducive to Z. intermedium presence on copepods in Chesapeake Bay, the largest estuary in North America. The York River tributary was sampled biweekly from fall 2014 through summer 2015 for plankton, peritrichs and bacteria in the water column. Bacterial abundance in the water column peaked in fall and late spring, coinciding with increased abundance and species richness of non-epibiont peritrichs. Among the plankton, only the calanoid copepods Acartia tonsa and Centropages hamatus were colonized by Z. intermedium. The peritrich epibiont displayed higher colonization rates on C. hamatus even when A. tonsa was far more abundant. Multivariate correlation analysis of infestation prevalence on A. tonsa showed a strong correlation with dissolved oxygen, salinity and water temperature. Such correlations, along with differences in host species biology, might be driving the seasonality of this epibiotic relationship.