In recent decades, the global intensification of marine heatwaves has impacted several ecosystems and species, including the endemic Mediterranean seagrass Posidonia oceanica. However, the scarcity of research in Eastern Mediterranean meadows, where historical and present thermal conditions differ from those of the Western Mediterranean, hampers our ability to draw comprehensive conclusions regarding the species' response to elevated sea temperatures. Here, we studied flowering patterns of P. oceanica meadows (3–15 m depth) of the Greek seas and assessed their potential association with marine heatwaves, while also examining the effects on plant growth associated with the transition from vegetative to sexual reproduction. To do so, we reconstructed flowering patterns from 2007 to 2021 across 58 meadows using lepidochronology and estimated summer marine heatwave metrics and categories using satellite sea surface temperature. The results revealed that flowering, while sporadic in most meadows (mean flowering frequency: 0.15), it was triggered by strong (Category II) summer marine heatwaves and a cumulative intensity exceeding 30°C days. Nevertheless, flowering density was low (mean flowering density: 11 inflorescences m−2) and not fuelled by frequency, intensity, or duration of marine heatwaves. Despite the potential long‐term benefits of sexual reproduction, annual rhizome production of flowering shoots decreased 1.5‐fold for at least 2 yr postflowering. This study uncovers the susceptibility of Eastern Mediterranean P. oceanica meadows, akin to their western counterparts, to marine heatwaves induced stress and its effects on reproductive strategies, raising concerns about the prospective plant growth and reproductive fitness to the escalating trend in marine heatwaves.

中文翻译：

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强烈的海洋热浪引发海草开花


近几十年来，全球海洋热浪的加剧影响了多个生态系统和物种，包括特有的地中海海草Posidonia oceanica。然而，由于东地中海草甸的历史和当前热条件与西地中海不同，因此缺乏研究，这阻碍了我们就该物种对海水温度升高的反应得出全面结论的能力。在这里，我们研究了希腊海域 P. oceanica 草甸（3-15 m 深）的开花模式，评估了它们与海洋热浪的潜在关联，同时还研究了从营养繁殖到有性繁殖的转变对植物生长的影响。为此，我们使用鳞纹年代学重建了 2007 年至 2021 年 58 个草地的开花模式，并使用卫星海面温度估计了夏季海洋热浪指标和类别。结果显示，虽然大多数草甸开花是零星的（平均开花频率：0.15），但开花是由强烈（II类）夏季海洋热浪和累积强度超过30°C的天数引发的。然而，开花密度较低（平均开花密度：11 个花序 m−2），并且不受海洋热浪的频率、强度或持续时间的推动。尽管有性繁殖具有潜在的长期益处，但在花后至少 2 年里，花芽的年根茎产量下降了 1.5 倍。这项研究揭示了东地中海 P. oceanica 草甸（类似于西方草甸）对海洋热浪引起的应激的敏感性及其对繁殖策略的影响，引起了人们对海洋热浪不断升级趋势的未来植物生长和繁殖适应性的担忧。