The peritrich epibiont Epistylis sp. is commonly found attached to the dominant copepod Pseudodiaptomus stuhlmanni in the St Lucia Estuary, South Africa. Experiments were conducted during 2014 and 2015 to determine the host specificity and host density dependence of Epistylis sp. and the relationship between this epibiont and the survivorship of P. stuhlmanni. Mixed culture experiments with the copepods P. stuhlmanni, Acartiella natalensis and Oithona brevicornis resulted in the exclusive attachment of Epistylis sp. to P. stuhlmanni. In contrast, no zooplankton hosted Epistylis sp. in mixed cultures with P. stuhlmanni and the mysid Mesopodopsis africana. Monoculture experiments with each of the above species also resulted in attachment only to P. stuhlmanni. Prevalence was significantly higher in P. stuhlmanni adults when compared with copepodites. A positive relationship was observed between epibiont prevalence and P. stuhlmanni density. High epibiont cover was associated with low survivorship of P. stuhlmanni. Individuals with a low epibiont cover had a higher survivorship, which was not statistically different from that of non-hosting individuals. These results suggest that Epistylis sp. has the potential to shape the zooplankton community structure and to influence the pelagic food web of the St Lucia Estuary.