1. Freshwater ecosystems are experiencing shifts in the natural range and variation of water temperatures due to anthropogenic activity, and these shifts can negatively affect survival, growth, and reproduction of aquatic species. Among the groups most affected are freshwater mussels of the family Unionidae. Knowledge of sublethal and lethal effects on mussels from changes in water temperature are largely unknown, especially for species from arid and semi‐arid regions such as the south‐western U.S.A. This limits the ability to assess, forecast, and adaptively manage this threat for those species and to understand how temperature influences population performance and community structure.
2. To determine the effects of elevated water temperature on mussels from the south‐western U.S.A., we evaluated the upper thermal tolerances of adults of three species (Amblema plicata, Cyclonaias necki, and Fusconaia mitchelli) from the Guadalupe River. Mussels were acclimated to 27°C and then tested across a range of experimental temperatures (30–39°C) in standard acute (96‐hr) and chronic (10‐day) laboratory tests. The acute and chronic thresholds identified in thermal tolerance testing were then related to in situ water temperature and flows using a uniform continuous above‐threshold analysis, which evaluates the duration and frequency of continuous events above a specified temperature threshold.
3. Median lethal temperature in 96‐hr tests averaged 36.4°C and ranged from 33.7 to 37.5°C, while the chronic 10‐day tests averaged 35.9°C and ranged from 32.4 to 37.5°C. Thermal tolerances of F. mitchelli were significantly lower than both A. plicata and C. necki, and the uniform continuous above‐threshold analysis showed that temperature affecting 5% of the population thresholds were exceeded for F. mitchelli in the Guadalupe River at both acute (96‐hr) and chronic (10‐day) values (30.5 and 28.4°C, respectively).
4. Findings from this study indicate that freshwater mussels from the arid and semi‐arid regions of the south‐west U.S.A. are already at risk from rising environmental temperatures and altered hydrology. However, by incorporating laboratory thermal tolerance estimates with in situ temperature and discharge data, we provide a range of hydrologic thresholds to inform environmental flow recommendations and potentially mitigate thermal stress occurring during periods of low flow. In addition, this method can be readily adapted to other arid regions to guide flow recommendations or assess whether flow standards are sufficient to protect freshwater mussel populations during severe droughts and low flow periods.

中文翻译：

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链接淡水贻贝的流量和热上限，以告知环境流量基准

1. 由于人为活动，淡水生态系统正在经历自然范围的变化和水温的变化，这些变化会对水生物种的生存，生长和繁殖产生负面影响。在受影响最严重的人群中，有Unidaidae家族的淡水贻贝。水温变化对贻贝的亚致死作用和致死作用的知识尚不清楚，尤其是对于干旱和半干旱地区的物种，例如美国西南部地区。物种并了解温度如何影响种群表现和群落结构。
2. 为了确定水温升高对来自美国西南部的贻贝的影响，我们评估了瓜达卢佩河的三种物种（皱纹Am，圆环蚤和米氏菌）的成虫的较高耐热性。贻贝适应27°C的温度，然后在标准的急性（96小时）和慢性（10天）实验室测试中，在一系列实验温度（30–39°C）中进行测试。然后，使用统一的连续阈值以上分析法，将在热耐受性测试中确定的急性和慢性阈值与原位水温和流量相关联，该分析方法可评估超过指定温度阈值的连续事件的持续时间和频率。
3. 在96小时的测试中，平均致死温度平均为36.4°C，范围为33.7至37.5°C，而长期的10天测试的平均致死温度平均为35.9°C，范围为32.4至37.5°C。F. mitchelli的热耐受性均显着低于A. plicata和C.ecki，并且统一的连续高于阈值分析显示，瓜达卢佩河的急性温度均超过了影响5％人口阈值的温度。（96小时）和慢性（10天）值（分别为30.5和28.4°C）。
4. 这项研究的结果表明，来自美国西南部干旱和半干旱地区的淡水贻贝已经面临环境温度升高和水文学改变的危险。但是，通过将实验室的热容忍估计值与原位温度和排放数据结合起来，我们提供了一系列水文阈值，可为环境流量建议提供依据，并有可能缓解低流量时期发生的热应力。此外，这种方法可以很容易地适应其他干旱地区，以指导流量建议或评估流量标准是否足以在严重干旱和低流量时期保护淡水贻贝种群。