In the Western Baltic Sea, climate change is happening at much faster rate than in most other seas and organisms are additionally exposed to a steep and variable salinity gradient. Climate change has previously been shown to affect parasite transmission in other marine ecosystems, yet little is known about potential effects of warming and desalination on parasite–host interactions. In laboratory experiments, we determined the combined effects of projected seawater warming and freshening on the emergence, activity, survival, and infectivity of cercariae (free-swimming infectious stage) of the trematode Himasthla elongata (Mehlis 1831), shed from its first intermediate host, the periwinkle Littorina littorea (Linnaeus 1758), in the Baltic Sea. We also assessed the susceptibility of the second intermediate host, the mussel Mytilus edulis Linnaeus, 1758, to cercarial infections. Generally, salinity was the main driver, particularly of cercarial activity, infectivity, and mussel susceptibility to infection. At the lowest salinity (13), cercariae were 50% less active compared to the highest salinity (19). Infection success and host susceptibility followed a similar pattern, with 47% and 43% less metacercariae (encysted stage) present at salinity 13 than at salinity 19, respectively. In contrast, effects of simulated warming were found only for cercarial survival, with cercarial longevity being higher at 19 than at 23 °C. No significant interactions between temperature and salinity were found. In contrast to the literature, the results suggest that a climate change-driven freshening (partly also warming) may lead to a general decline of marine trematodes, with possible beneficial effects for the involved hosts.

中文翻译：

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清新而不是变暖会驱使吸虫从长春花传播到贻贝

在西波罗的海，气候变化的发生速度比大多数其他海洋快得多，而且生物还暴露在陡峭且多变的盐度梯度中。先前已证明气候变化会影响其他海洋生态系统中的寄生虫传播，但人们对变暖和海水淡化对寄生虫-宿主相互作用的潜在影响知之甚少。在实验室实验中，我们确定了预计的海水变暖和清新对从其第一个中间宿主脱落的吸虫长条形吸虫（Mehlis 1831）尾蚴（自由游动感染阶段）的出现、活动、存活和感染性的综合影响，长春花 Littorina littorea (Linnaeus 1758)，在波罗的海。我们还评估了第二中间宿主贻贝 Mytilus edulis Linnaeus 的易感性，1758年，到尾蚴感染。一般来说，盐度是主要的驱动因素，特别是尾蚴活动、传染性和贻贝对感染的易感性。在最低盐度 (13) 下，尾蚴的活性比最高盐度 (19) 低 50%。感染成功和宿主易感性遵循类似的模式，在盐度 13 时存在的包蚴（包囊期）分别比在盐度 19 时少 47% 和 43%。相比之下，模拟变暖的影响仅对尾蚴存活率产生影响，尾蚴寿命在 19°C 时高于 23°C。未发现温度和盐度之间存在显着的相互作用。与文献相反，结果表明气候变化驱动的清新（部分也是变暖）可能导致海洋吸虫的普遍减少，