Booth J M, Giomi F, Daffonchio D, McQuaid C D, Fusi M
Coastal Research Group, Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa.
Via Maniciati, 6, Padova, Italy.
Sci Total Environ. 2023 May 10;872:162135. doi: 10.1016/j.scitotenv.2023.162135. Epub 2023 Feb 11.
Environmental fluctuation forms a framework of variability within which species have evolved. Environmental fluctuation includes predictability, such as diel cycles of aquatic oxygen fluctuation driven by primary producers. Oxygen availability and fluctuation shape the physiological responses of aquatic animals to warming, so that, in theory, oxygen fluctuation could influence their thermal ecology. We describe annual oxygen variability in agricultural drainage channels and show that disruption of oxygen fluctuation through dredging of plants reduces the thermal tolerance of freshwater animals. We compared the temperature responses of snails, amphipods, leeches and mussels exposed to either natural oxygen fluctuation or constant oxygen in situ under different acclimation periods. Oxygen saturation in channel water ranged from c. 0 % saturation at night to >300 % during the day. Temperature showed normal seasonal variation and was almost synchronous with daily oxygen fluctuation. A dredging event in 2020 dramatically reduced dissolved oxygen variability and the correlation between oxygen and temperature was lost. The tolerance of invertebrates to thermal stress was significantly lower when natural fluctuation in oxygen availability was reduced and decoupled from temperature. This highlights the importance of natural cycles of variability and the need to include finer scale effects, including indirect biological effects, in modelling the ecosystem-level consequences of climate change. Furthermore, restoration and management of primary producers in aquatic habitats could be important to improve the thermal protection of aquatic invertebrates and their resistance to environmental variation imposed by climate change.
环境波动形成了一个变异性框架，物种在这个框架内进化。环境波动包括可预测性，例如由初级生产者驱动的水生氧气波动的昼夜循环。氧气的可利用性和波动塑造了水生动物对变暖的生理反应，因此，从理论上讲，氧气波动可能会影响它们的热生态学。我们描述了农业排水渠道中的年度氧气变异性，并表明通过疏浚植物破坏氧气波动会降低淡水动物的热耐受性。我们比较了在不同驯化期内，暴露于自然氧气波动或原位恒定氧气环境下的蜗牛、双足类动物、水蛭和贻贝的温度反应。渠道水中的氧气饱和度范围从夜间的约0%饱和度到白天的>300%。温度呈现正常的季节性变化，并且几乎与每日氧气波动同步。2020年的一次疏浚事件显著降低了溶解氧变异性，氧气与温度之间的相关性也消失了。当氧气可利用性的自然波动减少并与温度解耦时，无脊椎动物对热应激的耐受性显著降低。这凸显了变异性自然循环的重要性，以及在模拟气候变化的生态系统层面后果时纳入更精细尺度效应（包括间接生物效应）的必要性。此外，恢复和管理水生生境中的初级生产者对于提高水生无脊椎动物的热保护能力及其对气候变化带来的环境变化的抵抗力可能很重要。
