Mortality of Corophium volutator (Amphipoda) caused by infestation with Maritrema subdolum (Digenea, Microphallidae) - laboratory studies

The impact of Maritrema subdolum Jagerskiold, 1908 on Corophium volutator P allas, 1766 was examined under laboratory conditions. Adult specimens of C. volutator were placed in petri dishes and exposed to different numbers (3, 10, 30, 50, 100, 150, 200) of recently emerged cercariae df the microphall id trematode M. subdolum. Addition of the same number of cercariae to the d ishes was repeated every second day until the crustaceans died. The experim ents revealed a strong negative correlation between the density of cercaria e in the dish and the average survival times of C. volutator. Amphipods exp osed to cercariae densities of 200 cercariae per 9.6 cm(2) died after 1.6 d (+/-0.5 SD) whereas specimens exposed to cercariae densities of 30 cercari ae per 9.6 cm2 died after 35.8 d (+/-7.1 SD), All dead C, volutator were in spected for larval M, subdolum. Highest infestation intensities of approxim ately 80 larval hi. subdolum were found in the test group to which 50 cerca riae were added every second day. In other test groups, where C. volutator was exposed to either higher or lower cercariae densities, the specimens ha rboured fewer larval trematodes when they died. Not yet encysted metacercar iae seemed to affect C. volutator in a more detrimental manner than encyste d metacercariae. Changes in the behaviour of the infested crustaceans were observed during the experiments. Heavily infested specimens had problems wi th swimming and crawling in the normal way. All results are discussed in re lation to field data. Mass mortality of C, volutator as a result of M. subd olum infestation seems to be an exceptional but conceivable occurrence in s hallow water areas of the Baltic Sea.