Ecological Relationships Between the Valviferan IsopodEdotia doellojuradoiGiambiagi, 1925, and its HostMytilus edulis chilensisin the Falkland Islands

A hitherto undescribed association between the valviferan isopod,Edotia doellojuradoi, and the mussel,Mytilus edulis chilensis, in the Falkland Islands (South-west Atlantic) is reported. Isopods were recorded within the mantle cavity of mussels from an estuarine location, Camilla Creek, and from two coastal sites, Goose Green and Darwin. All the mussel populations sampled along the estuary harboured isopods, whereas only those from the low and low-mid shore sites at Darwin and Goose Green were infested. Overall infestation increased between October 1994 and December 1995 from 47, 9 and 2 to 51, 21 and 24% at Camilla Creek, Goose Green and Darwin, respectively. Infestation also increased with decreasing tidal elevation but declined with mussel size. There was no apparent correlation between the occurrence of the isopod and salinity along the estuary at Camilla Creek. Isopod abundance increased with mussel size at all sites and tidal levels, and the largest broods were generally present in mussels from the low shore. Length-frequency distributions of the isopod populations were distinctly bimodal and comprised a prominent mode of males and juvenile individuals, up to 9 mm in size, and a smaller mode containing the adult females, ranging from 5 to 14 mm. Never more than one female was found within any given mussel, and this was always the largest isopod present. No significant differences in condition were observed between mussels that were infested and those that were not.