In addition to a rise in mean air and water temperatures, more frequent and intense extreme climate events (such as heat waves) have been recorded around the globe during the past decades. These environmental changes are projected to further intensify in the future, and we still know little on how they will affect ecological processes driving harmful cyanobacterial bloom formation. Therefore, we conducted a long-term experiment in 400L shallow freshwater mesocosms, where we evaluated the effects of a constant +4°C increase in mean water temperatures and compared it with a fluctuating warming scenario ranging from 0 to +8°C in the short-term (i.e., including heat waves) but with the same +4°C long-term elevation in mean water temperatures. We focused on investigating not only warming effects on cyanobacterial pelagic dynamics (phenology and biomass levels), but also on their recruitment from sediments - a fundamental part of their life-history and whose response to warming remains largely unexplored. Our results demonstrate that (1) a warmer environment not only induces a seasonal advancement and boosts biomass levels of specific cyanobacterial species in the pelagic environment, but also increases their recruitment rates from the sediments, and (2) these species-specific benthic and pelagic processes respond differently depending on whether climate warming is expressed only as an increase in mean water temperatures or, in addition, through an increased warming variability (including heat waves). These results are important because they show, for the first time, that climate warming can affect cyanobacterial dynamics at different life-history stages, all the way from benthic recruitment up to their establishment in the pelagic community. Furthermore, it also highlights that both cyanobacterial benthic recruitment and pelagic biomass dynamics may be different as a result of changes in the variability of warming conditions. We argue that these findings are a critical first step to further our understanding of the relative importance of increased recruitment rates for harmful cyanobacterial bloom formation under different climate change scenarios.

中文翻译：

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气候变暖和热浪改变了底栖-远洋界面上有害的蓝藻水华

除了平均气温和水温上升之外，在过去几十年中，全球还记录了更频繁和更剧烈的极端气候事件（如热浪）。这些环境变化预计在未来会进一步加剧，但我们对它们将如何影响导致有害蓝藻水华形成的生态过程知之甚少。因此，我们在 400 升浅层淡水中层世界进行了一项长期实验，我们评估了平均水温持续增加 +4°C 的影响，并将其与 0 至 +8°C 的波动变暖情景进行了比较。短期（即，包括热浪）但平均水温长期升高 4°C。我们不仅专注于研究变暖对蓝藻中上层动力学（物候和生物量水平）的影响，而且还研究它们从沉积物中的补充——这是它们生活史的基本组成部分，其对变暖的反应在很大程度上仍未得到探索。我们的结果表明 (1) 较温暖的环境不仅会导致季节性推进并提高远洋环境中特定蓝藻物种的生物量水平，而且还会增加它们从沉积物中的补充率，以及 (2) 这些特定物种的底栖和远洋根据气候变暖是仅表现为平均水温的升高，还是通过变暖变异性的增加（包括热浪），过程的反应会有所不同。这些结果很重要，因为它们第一次表明，气候变暖会影响不同生活史阶段的蓝藻动态，从底栖招募到它们在远洋群落中的建立。此外，它还强调，由于变暖条件的变化，蓝藻底栖补充和远洋生物量动态可能不同。我们认为，这些发现是进一步了解在不同气候变化情景下增加有害蓝藻水华形成的补充率的相对重要性的关键第一步。它还强调，由于变暖条件的变化，蓝藻底栖补充和浮游生物量动态可能不同。我们认为，这些发现是进一步了解在不同气候变化情景下增加有害蓝藻水华形成的补充率的相对重要性的关键第一步。它还强调，由于变暖条件的变化，蓝藻底栖补充和浮游生物量动态可能不同。我们认为，这些发现是进一步了解在不同气候变化情景下增加有害蓝藻水华形成的补充率的相对重要性的关键第一步。