Terrestrial plants are sensitive indicators of global warming because their annual cycles of growth and senescence are changing as warming proceeds. Single celled algae are distinct life forms capable of population bursts in any season, so there is uncertainty about phytoplankton phenology as a comparable indicator of global warming. We analyzed 4+ decades of monthly chlorophyll a measurements at two sites in San Francisco Bay and found abrupt shifts during summer months leading to a 48-day advance in the annual pattern of chlorophyll-a accumulation at one site and a 36-day delay at the other. These large phenological changes were not associated with changing temperature, but they were associated with changes in top–down control by bivalve filter feeders as biological communities were restructured by (1) introduction of a non-native clam, and (2) a shift in atmospheric forcing of the NE Pacific. This study illustrates that changes in phytoplankton phenology are not necessarily responses to or indicators of global warming. However, they can be indicators of human disturbances and natural climate oscillations having effects large enough to mask the effect of climate warming.

中文翻译：

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浮游植物作为全球变暖的指标？

陆地植物是全球变暖的敏感指标，因为它们的生长和衰老周期随着变暖的进行而发生变化。单细胞藻类是独特的生命形式，能够在任何季节种群数量激增，因此浮游植物物候作为全球变暖的可比指标存在不确定性。我们分析了 4+ 十年的每月叶绿素a在旧金山湾的两个地点进行的测量发现，夏季月份中的突然变化导致一个地点叶绿素-a 积累的年度模式提前 48 天，而另一个地点则延迟 36 天。这些大的物候变化与温度变化无关，但它们与双壳类滤食性自上而下控制的变化有关，因为生物群落通过以下方式重组：（1）引入非本地蛤，（2）东北太平洋的大气强迫。这项研究表明，浮游植物物候的变化不一定是对全球变暖的反应或指标。然而，它们可以作为人类干扰和自然气候波动的指标，其影响足以掩盖气候变暖的影响。