SOME ASPECTS OF THE ECOLOGY OF PACHYPYGUS GIBBER (COPEPODA), AN ASSOCIATED ORGANISM OF CIONA-INTESTINALIS (UROCHORDATA)

The ecological parameters of the association between the Urochordata C iona intestinalis and he copepod Pachypygus gibber are investigated. T his associated organism displays an aggregated distribution on the hos t population, and preferential site location within host individuals. The sex ratio observed is female biased. Even though this copepod live s al the expense of its host's feeding, the mean abundance and varianc e to the mean abundance ratio beta increase with host size, suggesting that the accumulation of this crustacean has no significant effect on either its host survival or growth. Although this associated copepod displays ecological features of parasites, ii could be considered as a non costly partner.