Freshwater Research Centre, PO Box 43966, Scarborough, 7975, South Africa; University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa.
Freshwater Research Centre, PO Box 43966, Scarborough, 7975, South Africa.
J Therm Biol. 2021 Apr;97:102890. doi: 10.1016/j.jtherbio.2021.102890. Epub 2021 Feb 21.
Compared to other climate regions of the world, Mediterranean regions are likely to experience more severe effects of climate change as rainfall decreases and temperatures increase. Global climate change models predict a reduction in rainfall and rise in the temperature of rivers in South Africa's Cape Fold Ecoregion (CFE) - a Mediterranean region in the south-west corner of the country. In the climate change context and with the prediction that stream temperatures will increase, determining thermal thresholds of freshwater fish in relation to their thermal history is a key element in understanding the potential impacts climate change and a rise in stream temperatures will have on already threatened freshwater fish. The ability of aquatic species to withstand warming in the CFE will be determined by its upper tolerance limit (critical thermal maximum, CT). A fish's CT can be influenced by several factors, including the thermal characteristics of its environment (thermal history). In this study, we set out to examine whether the thermal tolerance of an endemic CFE fish species, the Cape Galaxias, Galaxias zebratus Castelnau, 1861, is influenced by its thermal history. We hypothesised that CT of G. zebratus individuals from warmer sites will have higher CT values than individuals from cooler sites. Hourly in situ water temperature data were collected and the CT values were determined for fish (n = 15 per site) from ten sites on six rivers on the Cape Peninsula of the CFE, and regression analyses revealed that G. zebratus upper thermal tolerance limits are indeed significantly influenced by its thermal history (as characterised by the seven day moving average of daily mean, Mean_7). CT was positively related to the thermal history of the rivers, indicating that G. zebratus, and potentially other stenothermic CFE freshwater fish species, is likely to be particularly vulnerable to climate warming. These findings broaden our understanding of thermal history patterns on fish thermal tolerances in Mediterranean rivers, and support G. zebratus conservation by determining its biological temperature thresholds and thermal requirements. Thermal data should be used to monitor and manage stream temperatures to ensure Mediterranean stenotherms can persist in their natural environment.
与世界上其他气候区相比，地中海地区可能会受到气候变化更严重的影响，因为降雨量减少，气温升高。全球气候变化模型预测，南非开普褶皱生态区（CFE）——该国西南角的一个地中海地区——的河流降雨量减少，气温上升。在气候变化的背景下，随着预测溪流温度将升高，确定淡水鱼类与热历史相关的热阈值是了解气候变化和溪流温度升高对已经受到威胁的淡水鱼类潜在影响的关键因素。水生物种在 CFE 中承受变暖的能力将取决于其上限耐受极限（临界热最大值，CT）。鱼类的 CT 可以受到多种因素的影响，包括其环境的热特性（热历史）。在这项研究中，我们着手研究 CFE 特有鱼类——开普加拉西亚鱼（Galaxias zebratus Castelnau，1861）的耐热性是否受到其热历史的影响。我们假设，来自较温暖地点的 G. zebratus 个体的 CT 值将高于来自较冷地点的个体。我们收集了每小时现场水温数据，并确定了来自 CFE 开普半岛六条河流十个地点的 15 条鱼（每条鱼一个地点）的 CT 值，回归分析表明，G. zebratus 的上热耐受极限确实受到其热历史的显著影响（由每日平均的七天移动平均值，Mean_7 来描述）。CT 与河流的热历史呈正相关，这表明 G. zebratus 以及可能的其他 CFE 淡水鱼类可能特别容易受到气候变暖的影响。这些发现拓宽了我们对地中海河流中鱼类热耐受的热历史模式的理解，并通过确定其生物学温度阈值和热需求来支持 G. zebratus 的保护。应使用热数据来监测和管理溪流温度，以确保地中海的狭温动物能够在其自然环境中生存。
