DataSheet_1_The combined effects of acidification and acute warming on the embryos of Pacific herring (Clupea pallasii).docx

Anthropogenic climate change is projected to affect marine ecosystems by challenging the environmental tolerance of individuals. Marine fishes may be particularly vulnerable to emergent climate stressors during early life stages. Here we focus on embryos of Pacific herring (Clupea pallasii), an important forage fish species widely distributed across the North Pacific. Embryos were reared under a range of temperatures (10-16°C) crossed with two pCO2 levels (600 and 2000 μatm) to investigate effects on metabolism and survival. We further tested how elevated pCO2 affects critical thermal tolerance (CTmax) by challenging embryos to short-term temperature fluctuations. Experiments were repeated on embryos collected from winter and spring spawning populations to determine if spawning phenology corresponds with different limits of environmental tolerance in offspring. We found that embryos could withstand acute exposure to 20°C regardless of spawning population or incubation treatment, but that survival was greatly reduced after 2-3 hours at 25°C. We found that pCO2 had limited effects on CTmax. The survival of embryos reared under chronically warm conditions (12°, 14°, or 16°C) was significantly lower relative to 10°C treatments in both populations. Oxygen consumption rates (MO2) were also higher at elevated temperatures and pCO2 levels. However, heart contraction measurements made 48 hours after CTmax exposure revealed a greater increase in heart rate in embryos reared at 10°C compared to 16°C, suggesting acclimation at higher incubation temperatures. Our results indicate that Pacific herring are generally tolerant of pCO2 but are vulnerable to acute temperature stress. Importantly, spring-spawning embryos did not clearly exhibit a higher tolerance to heat stress compared to winter offspring.

人为气候变化被预测将通过挑战个体的环境耐受限度对海洋生态系统造成影响。海洋鱼类在早期生活史阶段或许尤其易受新增气候胁迫因子的侵袭。本研究聚焦于太平洋鲱（Clupea pallasii）的胚胎——这是广泛分布于北太平洋的重要饵料鱼种。我们将胚胎置于一系列温度梯度（10-16℃）与两种二氧化碳分压（pCO2，600和2000 μatm）的交叉处理组中饲养，以探究其对代谢与存活的影响。我们进一步通过短期温度波动胁迫胚胎，检测升高的pCO2对临界热耐受限度（CTmax）的作用。此外，我们利用采集自冬季和春季产卵种群的胚胎重复实验，以明确产卵物候是否与子代的不同环境耐受限度存在关联。研究结果显示，无论产卵种群或孵化处理类型如何，胚胎均可耐受20℃的急性暴露，但在25℃下暴露2-3小时后存活率大幅下降。我们发现pCO2对CTmax的影响较为有限。相较于10℃处理组，长期处于高温环境（12、14或16℃）的胚胎存活率在两个种群中均显著降低。耗氧率（MO2）在升高的温度和pCO2条件下同样更高。不过，在临界热耐受胁迫后48小时测得的心脏收缩指标显示，10℃孵化组胚胎的心率增幅高于16℃组，这表明更高的孵化温度下存在驯化效应。本研究结果表明，太平洋鲱整体对pCO2具备耐受性，但易受急性温度胁迫影响。尤为重要的是，春季产卵胚胎并未比冬季子代表现出更显著的热胁迫耐受性。