The Hydrobia ulvae–Maritrema subdolum association: influence of temperature, salinity, light, water-pressure and secondary host exudates on cercarial emergence and longevity

Abstract

The effects of environmental factors and exudates from the amphipod Corophium volutator on the emergence of Maritrema subdolum cercariae (Digenea: Microphallidae) from the snail Hydrobia ulvae were investigated in the laboratory. Increasing the temperature (15 to 25 degrees C) caused an overall 11-fold increase in emergence rate under varying salinities (24 to 36 per thousand). The effect of salinity depended on the experimental temperature. Emergence increased with increasing salinity at higher temperatures, but decreased with increasing salinity at 15 degrees C. Whereas the different levels of salinity had no effect, increasing the temperature significantly reduced the life span of cercariae. In comparison with complete darkness, light caused a two-fold increase in emergence, whereas an increment of the water pressure from 1.0 to 1.3 ATM (corresponding to 0 and 3 m of depth) left the shedding rate unaffected. Unidentified exudates from the second intermediate host, C. volutator, significantly depressed the cercarial emergence rate. The main transmission window of M. subdolum seems to occur during low water in tidal pools where light levels are high and solar radiation rapidly elevates the water temperature, as well as salinity through evaporation. The consequence of such a transmission strategy is discussed in relation to the impact of M. subdolum on the population dynamics of the second intermediate host.

Calcareous assemblages of the southeastern Mediterranean low-tide estuaries — Seasonal dynamics and paleo-environmental implications

“…Trematodes showed increased prevalences and mean intensities in spring and summer, coinciding with previous results (Mouritsen, 2002;Poulin, 2006). More interestingly, we detected increased prevalences in spring and autumn 2012 as well as increased mean intensities in spring 2012 in comparison with sampling in 2011.…”

“…Furthermore, if only time has an effect on macroparasite accumulation we should have observed increased infection rates for all macroparasite species and not mainly for those that have been shown to adjust their life cycle to temperature (e.g. trematodes, see Sankurathri and Holmes, 1976;Mouritsen, 2002;Thieltges and Rick, 2006). As consequence, we have to be cautious in deriving generalities from these data.…”

Impact of trematodes on host survival and population density in the intertidal gastropod Zeacumantus subcarinatus

“…Normally, snails with mature Maritrema spp. infections will start shedding cercariae within a few hours under these conditions (Mouritsen 2002, this study). Uninfected snails were tested again after 8 d to verify their infection status.…”

Parasite co-infection of two sympatric bivalves, the Manila clam (Ruditapes philippinarum) and the cockle (Cerastoderma edule) along a latitudinal gradient

“…Digeneans also have population dynamics influenced by temperature. Indeed, release of trematode from the first intermediate host and successful transmission to the second intermediate host are highly temperature-dependent (Mouritsen and Jensen 1997;Mouritsen 2002). Accordingly, a study on Maritrema novaezelandensis reported that cercariae emergence from the gastropod Zeacumantus subcarinatus increases threefold when temperature rises from 19…”

“…distribution between the studied sites. Cercarial emission in the digenean life cycle increases with salinity but no effect has been detected on cercaria life span (Mouritsen 2002). For these two major environmental factors, protozoans and digeneans therefore are favoured by high temperature and high salinity.…”