DAO 35:47-52 (1999)  -  doi:10.3354/dao035047

ABSTRACT: The impact of Maritrema subdolum Jägerskiöld, 1908 on Corophium volutator Pallas, 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 of the microphallid trematode M. subdolum. Addition of the same number of cercariae to the dishes was repeated every second day until the crustaceans died. The experiments revealed a strong negative correlation between the density of cercariae in the dish and the average survival times of C. volutator. Amphipods exposed to cercariae densities of 200 cercariae per 9.6 cm² died after 1.6 d (±0.5 SD) whereas specimens exposed to cercariae densities of 30 cercariae per 9.6 cm² died after 35.8 d (±7.1 SD). All dead C. volutator were inspected for larval M. subdolum. Highest infestation intensities of approximately 80 larval M. subdolum were found in the test group to which 50 cercariae were added every second day. In other test groups, where C. volutator was exposed to either higher or lower cercariae densities, the specimens harboured fewer larval trematodes when they died. Not yet encysted metacercariae seemed to affect C. volutator in a more detrimental manner than encysted metacercariae. Changes in the behaviour of the infested crustaceans were observed during the experiments. Heavily infested specimens had problems with swimming and crawling in the normal way. All results are discussed in relation to field data. Mass mortality of C. volutator as a result of M. subdolum infestation seems to be an exceptional but conceivable occurrence in shallow water areas of the Baltic Sea.

KEY WORDS: Corophium volutator · Maritrema subdolum · Mortality · Digenea · Microphallidae · Parasitism · Population dynamics