In coastal areas with estuarine influence, exposure to hypo-osmotic conditions may affect larval survival, development and growth. Most knowledge about effects of reduced salinity on coastal organisms is based on keeping individuals under constant conditions in the laboratory. By contrast, little is known about the effects of more realistic situations where organisms are exposed to low salinity over short time scales. Such environmental short-term fluctuations are expected to increase due to climate change. Here, we experimentally evaluated the sublethal effects of both short-term and continuous exposure to moderately reduced salinities (salinity 20 and 25; compared to seawater, salinity 32) in larvae of European lobster Homarus gammarus. Total body dry mass and biochemical composition (measured as: protein and lipid contents) were measured as response variables in Mysis stages I to III. Short-term effects of low salinity were quantified in a group of larvae kept in seawater from hatching until the time of transfer to the test salinities. After ca. 40 % of each moult cycle in seawater (determined in preliminary experiments for Mysis I, II and III), larvae were assigned to a seawater control or reduced salinities lasting for 16 h (i.e. until ca. 50 % of the time spent within the moulting cycle). Effects of continuous exposure to low salinity were quantified when larvae were exposed to the different salinities from hatching, until they reached ca. 50 % of the successive moulting stage. Surprisingly, in the Mysis II and III stages, short-term exposure to low salinity had much stronger effects on accumulation of reserves than the continuous exposure. Such effects were manifested mostly as limited accumulation, or even losses, in the lipid content as compared to reductions in the amount of protein accumulated. The most sensitive stage to exposure to low salinity was the Mysis III; by contrast in Mysis I such effects were relative weak (not always significant). Chronic exposure to low salinity also led to an increase in developmental time especially at the advanced stages. Our results highlight the importance of quantifying effects of environmental fluctuations at different time scales in order to better understand how organisms cope with realistic environmental change in the coastal zones. For H. gammarus, our results suggest that larvae respond adaptively to low salinity by maintaining protein levels at expenses of reductions in lipid accumulation and by extending the developmental time, but the capacity to elicit a fully compensatory response varies ontogenetically.

中文翻译：

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短期和持续低盐度暴露对龙虾幼体 Homarus gammarus 生化成分的影响

在受河口影响的沿海地区，暴露于低渗条件可能会影响幼虫的存活、发育和生长。大多数关于降低盐度对沿海生物影响的知识是基于将个体保持在实验室中的恒定条件下。相比之下，对于生物体在短时间内暴露于低盐度的更现实情况的影响知之甚少。由于气候变化，这种环境短期波动预计会增加。在这里，我们通过实验评估了短期和持续暴露于适度降低的盐度（盐度 20 和 25；与海水相比，盐度 32）对欧洲龙虾 Homarus gammarus 幼虫的亚致死效应。全身干重和生化成分（测量为：蛋白质和脂质含量）被测量为糠秕病 I 至 III 期的响应变量。对一组从孵化到转移到测试盐度的海水中饲养的幼虫进行了量化。在大约之后。每个蜕皮周期的 40% 在海水中（在糠虾 I、II 和 III 的初步实验中确定），幼虫被分配到海水控制或持续 16 小时的降低盐度（即直到大约 50% 的时间在蜕皮内度过循环）。当幼虫从孵化开始暴露于不同的盐度，直到它们达到约 50 % 的连续换羽阶段。令人惊讶的是，在 Mysis II 和 III 阶段，与持续暴露相比，短期暴露于低盐度对储量积累的影响要强得多。与蛋白质积累量的减少相比，这种影响主要表现为脂质含量的有限积累，甚至损失。暴露于低盐度环境中最敏感的阶段是 Mysis III；相比之下，在 Mysis I 中，这种影响相对较弱（并不总是显着）。长期暴露于低盐度也导致发育时间增加，尤其是在晚期。我们的结果强调了量化不同时间尺度环境波动影响的重要性，以便更好地了解生物如何应对沿海地区的现实环境变化。对于 H. gammarus，