Biologische Anstalt Helgoland, Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Helgoland, Germany.
Kellerseestr. 38a, 23714, Bad Malente, Germany.
Zoology (Jena). 2021 Feb;144:125885. doi: 10.1016/j.zool.2020.125885. Epub 2020 Nov 30.
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.
在受河口影响的沿海地区，暴露于低渗环境可能会影响幼虫的生存、发育和生长。大多数关于低盐度对沿海生物影响的知识都是基于在实验室中将个体保持在恒定条件下获得的。相比之下，对于生物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连续暴露于适度低盐度（盐度 20 和 25；与海水盐度 32 相比）对欧洲龙虾 Homarus gammarus 幼虫的亚致死影响。在 I 至 III 期的糠虾阶段，将总体干质量和生化组成（以蛋白质和脂质含量测量）作为反应变量进行测量。在一组从孵化开始一直到转移到测试盐度的幼虫中，量化了低盐度的短期影响。在海水中进行大约 40%的每个蜕皮周期后（在糠虾 I、II 和 III 的初步实验中确定），将幼虫分配到海水对照或持续 16 小时的低盐度（即直到大约 50%的蜕皮周期内）。当幼虫从孵化开始就暴露于不同盐度，直到它们达到大约 50%的连续蜕皮阶段时，量化了连续暴露于低盐度的影响。令人惊讶的是，在糠虾 II 和 III 阶段，短期暴露于低盐度对储备积累的影响远大于连续暴露。这种影响主要表现为脂质含量的有限积累，甚至损失，而不是积累的蛋白质量的减少。对低盐度暴露最敏感的阶段是糠虾 III；相比之下，在糠虾 I 中，这种影响相对较弱（并不总是显著的）。慢性暴露于低盐度也会导致发育时间延长，尤其是在高级阶段。我们的结果强调了在不同时间尺度上量化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，我们的结果表明，幼虫通过维持蛋白质水平（以脂质积累减少为代价）并延长发育时间来适应低盐度，但诱发完全补偿反应的能力随个体发育而变化。
