Mytilus edulis chilensis infested with Coccomyxa parasitica (Chlorococcales, Coccomyxaceae)

The association between the green alga Coccomyxa parasitica (Chlorococcales ) and the mussel Mytilus edulis chilensis at Goose Green, Falkland Islands is reported. C. parasitica occurred within the soft tissues with an overall infestation rate of 16%. The highest levels of infestation (23%) occurred in individuals from the middle of the main mussel bed, with considerably lo wer levels of infestation in the upper and lower regions (<1% and 5% respec tively). No consistent seasonal pattern in infestation rate was detected be tween September 1993 and February 1996. C. parasitica was most commonly obs erved in tissues located in the posterior territory of the host, in areas m ost directly exposed to light. Tissues of infested mussels were rather wate ry and translucent and the adductor muscle appeared weak and stringy. Durin g the summer months when Falkland mussels are in peak reproductive conditio n, dry flesh weight of infested mussels was significantly lower than noninf ected mussels of comparable size suggesting that infestation by C. parasiti ca may reduce reproductive output. However it is uncertain whether poor con dition of the host is due to the presence of the parasitic alga or whether C. parasitica infests only those mussels that are already in poor condition .