Effects of temperature, salinity, and water level on the emergence of marine cercariae.

With the prospect of large-scale environmental changes, there is an urgent need to obtain information regarding environmental influences acting on the emergence of cercariae in marine systems. We investigated the response of trematodes of the intertidal snail Zeacumantus subcarinatus to altered temperature, salinity, and water level. The emergence of one trematode species, Maritrema novaezealandensis (Microphallidae), showed a weak trend to decrease with increased temperature; whereas, the emergence of a second species, Philophthalmus sp. (Philophthalmidae), increased at warmer temperatures. Both species exhibited increased cercarial emergence at the lowest salinity used (30 PSU). More M. novaezealandensis cercariae emerged when snails were kept partially submerged. In contrast, emergence of Philophthalmus sp. increased when snails were completely submerged. These results may reflect different transmission strategies employed by the two trematode species. Based on this model, we propose that trematode parasitism in intertidal zones is likely to be impacted by various changes in the marine environment resulting from global warming.