Davis Brittany E, Cocherell Dennis E, Sommer Ted, Baxter Randall D, Hung Tien-Chieh, Todgham Anne E, Fangue Nann A
Department of Wildlife, Fish and Conservation Biology, University of California Davis, Davis, CA, USA.
Department of Animal Sciences, University of California Davis, Davis, CA, USA.
Conserv Physiol. 2019 Feb 18;7(1):coy076. doi: 10.1093/conphys/coy076. eCollection 2019.
In many aquatic systems, native fishes are in decline and the factors responsible are often elusive. In the San Francisco Estuary (SFE) in California, interactions among native and non-native species are key factors contributing to the decline in abundance of endemic, endangered Delta Smelt (). Climate change and drought-related stressors are further exacerbating declines. To assess how multiple environmental changes affect the physiology of native Delta Smelt and non-native Mississippi Silverside () and Largemouth Bass (), fishes were exposed to serial exposures of a single stressor (elevated temperature or salinity) followed by two stressors (elevated temperature and salinity) to determine how a single stressor affects the capacity to cope with the addition of a second stressor. Critical thermal maximum (CTMax; a measure of upper temperature tolerance) was determined after 0, 2, 4 and 7 days following single and multiple stressors of elevated temperature (16°C vs. 20°C) and salinity (2.4 vs. 8-12 ppt, depending on species). Under control conditions, non-native fishes had significantly higher CTMax than the native Delta Smelt. An initial temperature or salinity stressor did not negatively affect the ability of any species to tolerate a subsequent multiple stressor. While elevated salinity had little effect on CTMax, a 4°C increase in temperature increased CTMax. Bass experienced an additive effect of increased temperature and salinity on CTMax, such that CTMax further increased under multiple stressors. In addition, Bass demonstrated physiological sensitivity to multiple stressors demonstrated by changes in hematocrit and plasma osmolality, whereas the physiology of Silversides remained unaffected. Non-native Bass and Mississippi Silversides showed consistently higher thermal tolerance limits than the native Delta Smelt, supporting their abundance in warmer SFE habitats. Continued increases in SFE water temperatures predicted with climate change may further impact endangered Delta Smelt populations directly if habitat temperatures exceed thermal limits.
在许多水生系统中，本地鱼类数量正在减少，而导致这种情况的因素往往难以捉摸。在加利福尼亚州的旧金山湾（SFE），本地物种与非本地物种之间的相互作用是导致特有濒危物种三角洲胡瓜鱼数量减少的关键因素。气候变化和与干旱相关的压力因素正在进一步加剧这种减少趋势。为了评估多种环境变化如何影响本地三角洲胡瓜鱼以及非本地密西西比银汉鱼和大口黑鲈的生理机能，研究人员让鱼类先后暴露于单一压力因素（温度升高或盐度升高）以及两种压力因素（温度升高和盐度升高）之下，以确定单一压力因素如何影响应对添加第二种压力因素的能力。在经历单一和多种温度升高（16°C 与 20°C）及盐度升高（2.4 与 8 - 12 ppt，具体取决于物种）压力因素后的第 0、2、4 和 7 天，测定了临界热最大值（CTMax；衡量温度耐受性上限的指标）。在对照条件下，非本地鱼类的 CTMax 显著高于本地三角洲胡瓜鱼。初始的温度或盐度压力因素并未对任何物种耐受后续多种压力因素的能力产生负面影响。虽然盐度升高对 CTMax 影响不大，但温度升高 4°C 会使 CTMax 增加。大口黑鲈在 CTMax 方面经历了温度和盐度升高的叠加效应，即在多种压力因素下 CTMax 进一步增加。此外，大口黑鲈通过血细胞比容和血浆渗透压的变化表现出对多种压力因素的生理敏感性，而银汉鱼的生理机能则未受影响。非本地大口黑鲈和密西西比银汉鱼始终表现出比本地三角洲胡瓜鱼更高的热耐受极限，这支持了它们在 SFE 较温暖栖息地中的丰富数量。随着气候变化预测 SFE 水温持续升高，如果栖息地温度超过热极限，可能会直接进一步影响濒危的三角洲胡瓜鱼种群。
