Detrimental effect of peritrich ciliates (Epistylis sp.) as epibionts on the survival of the copepod Acartia bifilosa

Abstract. Widespread epibiontic relationship is best known as a commensal relationship, but several studies have shown also harmful influences on hosts by epibionts. A laboratory experiment was carried out to investigate the effect of peritrich ciliates (Epistylis sp.) as epibionts on the survival of Acartia bifilosa (Copepoda). Copepods were collected from the Gulf of Riga and the trial was made in seawater taken from the same location as the zooplankton samples. Adult copepods were divided into four groups by sex and by infection with epibionts. Results of the trial suggest that animals infested with epibionts were less viable than the uninfested ones. This pattern was significant in the case of females, but not males. Comparison of performance by sexes showed that the survival rate was significantly higher among females than males. The results further suggest that epibiontic protozoans may also influence egg production of copepods, because of shorter life span of females, and therefore may play a substantial role in copepod production and community dynamics