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Response of three krill species to hypoxia and warming: an experimental approach to oxygen minimum zones expansion in coastal ecosystems

机译：三种磷虾对缺氧和变暖的响应：沿海生态系统中氧气最小区域扩展的实验方法

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To understand the adaptation of euphausiid (krill) species to oxygen minimum zones (OMZs), respiratory response and stress experiments combining hypoxia-reoxygenation exposure with warming were conducted. Experimental krill species were obtained from the Antarctic (South Georgia area), the Humboldt Current System (HCS, Chilean coast) and the Northern California Current System (NCCS, Oregon). Euphausia mucronata from the HCS showed oxyconforming pO2-dependent respiration below 80% air saturation (18kPa). Normoxic subsurface oxygenation in winter posed a ‘high oxygen stress’ for this species. The NCCS krill, Euphausia pacifica, and the Antarctic krill, Euphausia superba, maintained respiration rates constant down to low critical pO2 values of 6kPa (30% air saturation) and 11kPa (55% air saturation), respectively. Antarctic krill had low antioxidant enzyme activities, but high concentrations of the molecular antioxidant glutathione (GSH) and was not lethally affected by 6h exposure to moderate hypoxia. The temperate krill species (E.pacifica) had higher superoxide dismutase (SOD) values in winter than in summer, which relates to a higher winter metabolic rate. In all species, antioxidant enzyme activities remained constant during hypoxic exposure at the typical temperature for their habitat. Warming by 7°C above habitat temperature in summer increased SOD activities and GSH levels in E.mucronata (HCS), but no oxidative damage occurred. In winter, when the NCCS is well mixed and the OMZ is deeper, +4°C of warming combined with hypoxia represents a lethal condition for E.pacifica. In summer, when the OMZ expands upwards (100m subsurface), antioxidant defences counteracted hypoxia and reoxygenation effects in E.pacifica, but only at mildly elevated temperature (+2°C). In this season, experimental warming by +4°C reduced antioxidant activities and the combination of warming with hypoxia again caused mortality of exposed specimens. We conclude that a climate change scenario combining warming and hypoxia represents a serious threat to E.pacifica and, as a consequence, NCCS food webs.
机译：为了了解磷虾（磷虾）种类对最小氧区（OMZs）的适应性，进行了呼吸反应和应激实验，将缺氧-复氧暴露与变暖相结合。从南极（乔治亚州南部地区），洪堡洋流系统（HCS，智利海岸）和北加州洋流系统（俄勒冈州NCCS）获得了磷虾物种。来自HCS的Euphausia mucronata表现出低于80％的空气饱和度（18kPa）的依赖氧的pO2依赖呼吸。冬季常氧表面地下充氧给该物种造成了“高氧胁迫”。 NCCS磷虾（Euphausia pacifica）和南极磷虾（Euphausia superba）将呼吸速率保持恒定，分别降至6kPa（空气饱和度为30％）和11kPa（空气饱和度为55％）的低临界pO2值。南极磷虾具有较低的抗氧化酶活性，但高浓度的分子抗氧化剂谷胱甘肽（GSH）不受中等缺氧6h的致命影响。冬季的温带磷虾物种（E.pacifica）的超氧化物歧化酶（SOD）值高于夏季，这与冬季更高的代谢率有关。在所有物种中，在其栖息地的典型温度下低氧暴露期间，抗氧化酶的活性均保持恒定。夏季在高于栖息地温度7°C的条件下变暖，会增加大肠埃希菌（HCS）中的SOD活性和GSH含量，但未发生氧化损伤。在冬季，当NCCS充分混合并且OMZ更深时，+ 4°C的温度加上缺氧会导致大肠埃希氏菌的致死条件。在夏季，当OMZ向上扩展（地下100m）时，抗氧化剂防御作用抵消了大肠杆菌中的缺氧和复氧作用，但仅在温度略高时（+ 2°C）。在这个季节，+ 4°C的实验性增温降低了抗氧化活性，并且增温与缺氧相结合再次导致了暴露标本的死亡。我们得出的结论是，变暖和缺氧相结合的气候变化情景严重威胁着太平洋埃希氏菌，并因此威胁了NCCS食物网。

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