Relationship Between Calanoid Copepods and Epibiont Suctorian Ciliates in the North Pacific Ocean

Characteristics of those calanoids infested with suctorians and host specificity as well as attachment sites of suctorians were analyzed in detail. Calanoids were collected with a ring net vertically hauled from either 150 m or 1000 m to the surface in northern North Pacific Ocean from June to August 2012. A total of 258 individuals of calanoids belonging to fourteen species were found to be infested with suctorians. Almost all of them were adult females. These copepods are large and devoid of diapause phase or molting. Four species of suctorian ciliates were identified, Actinocyathula pleuromammae, Paracineta gaetani, Ephelota coronata, Rhabdophrya truncata and Acineta sp. Ephelota coronata infested only Metridia pacifica, a surface-dwelling copepod species, suggesting host specificity of this suctorian. Rhabdophrya truncata which occurred widely in the study area but infested only 2 calanoid species, Candacia columbiae and Paraeuchaeta elongata, and Acineta sp. which infested only 2 species belonging to one genus Paraeuchaeta.,P. birostrata and P. elongata, showed some host specificity. Attachment sites of copepod body was very specific for E. coronata (urosome of Metridia pacifica) and R. truncata (metasome in Candacia columbiae, and urosome in Paraeuchaeta elongata). A. pleuromammae infested 5 species and P. gaetani did 11species of calanoids. Cluster analysis showed that P. gaetani attached mainly to metasome of copepods irrespective of species or sea areas, while A. pleuromammae attached mainly to metasome, cephalosome and urosome of Gaetanus simplex and most of other calanoids, and mostly to metasome of Metridia pacifica. These differences in attachment sites may be caused by contact behavior of copepods, especially copulation, when swarmers of suctorians change hosts, or there may be preferred sites for suctorians.