Marine heatwaves threaten the persistence of kelp forests globally. However, the observed responses of kelp forests to these events have been highly variable on local scales. Here, we synthesize distribution data from an environmentally diverse region to examine spatial patterns of canopy kelp persistence through an unprecedented marine heatwave. We show that, although often overlooked, temperature variation occurring at fine spatial scales (i.e., a few kilometers or less) can be a critical driver of kelp forest persistence during these events. Specifically, though kelp forests nearly all persisted toward the cool outer coast, inshore areas were >3°C warmer at the surface and experienced extensive kelp loss. Although temperatures remained cool at depths below the thermocline, kelp persistence in these thermal refugia was strongly constrained by biotic interactions, specifically urchin populations that increased during the heatwave and drove transitions to urchin barrens in deeper rocky habitat. Urchins were, however, largely absent from mixed sand and cobble benthos, leading to an unexpected association between bottom substrate and kelp forest persistence at inshore sites with warm surface waters. Our findings demonstrate both that warm microclimates increase the risk of habitat loss during marine heatwaves and that biotic interactions modified by these events will modulate the capacity of cool microclimates to serve as thermal refugia.

中文翻译：

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面对直接和间接的海洋热浪效应，小气候预测海带森林灭绝

海洋热浪威胁着全球海带森林的持续存在。然而，观察到的海带林对这些事件的反应在局部范围内变化很大。在这里，我们综合了来自环境多样化地区的分布数据，以通过前所未有的海洋热浪检查冠层海带持久性的空间模式。我们表明，尽管经常被忽视，但发生在精细空间尺度（即几公里或更小）的温度变化可能是这些事件期间海带森林持续存在的关键驱动因素。具体来说，尽管海带森林几乎都向凉爽的外海岸延伸，但近海地区地表温度升高了 3°C 以上，海带大量流失。尽管在温跃层以下的深处温度保持凉爽，这些热避难所中的海带持久性受到生物相互作用的强烈限制，特别是在热浪期间增加的海胆种群并推动向更深岩石栖息地的海胆贫瘠地区过渡。然而，混合沙子和鹅卵石底栖生物中基本上不存在海胆，导致底部基质与海带林在具有温暖地表水的近岸地区的持久性之间存在意想不到的关联。我们的研究结果表明，温暖的小气候增加了海洋热浪期间栖息地丧失的风险，并且这些事件改变的生物相互作用将调节凉爽的小气候作为热避难所的能力。基本上不存在于混合沙子和鹅卵石底栖生物中，导致在具有温暖地表水的近岸地区，底部基质与海带林持久性之间存在意想不到的关联。我们的研究结果表明，温暖的小气候增加了海洋热浪期间栖息地丧失的风险，并且这些事件改变的生物相互作用将调节凉爽的小气候作为热避难所的能力。基本上不存在于混合沙子和鹅卵石底栖生物中，导致在具有温暖地表水的近岸地区，底部基质与海带林持久性之间存在意想不到的关联。我们的研究结果表明，温暖的小气候增加了海洋热浪期间栖息地丧失的风险，并且这些事件改变的生物相互作用将调节凉爽的小气候作为热避难所的能力。