The episodic stranding of millions of pelagic red crabs (Pleuroncodes planipes) along California beaches is a striking and puzzling phenomenon. Pleuroncodes planipes are usually abundant off Baja California, Mexico, and their appearance in central California is thought to coincide with anomalously warm waters and northward advection related to El Niño. This anecdotal association has stimulated many hypotheses, but no hypothesis has gained clear and convincing support. Motivated by an unprecedented number of P. planipes strandings and at-sea observations in 2015–2019, we compiled 10 P. planipes datasets spanning 1950–2019, tested the anomalous advection hypothesis using a transport analysis from 1981 to 2010, and explored other compelling hypotheses. We found P. planipes presence off central California was related to anomalous advection of waters from Mexico, sometimes but not always associated with El Niño events, with P. planipes likely remaining residents of northern waters for several years without additional anomalous transport but potentially facilitated by warm waters. By identifying a mechanism behind episodic P. planipes range expansions, we show that a source water index could provide an early indicator for anomalous events in the future.

中文翻译：

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异常的极地平流促进了北太平洋东部远洋红蟹的偶发范围扩张

数以百万计的远洋红蟹（Pleuroncodes planipes）在加利福尼亚海滩偶遇搁浅，这是一个引人注目且令人费解的现象。Pleuroncodes planipes通常在墨西哥下加利福尼亚州附近很丰富，它们在加利福尼亚州中部的出现被认为与异常温暖的海水和与厄尔尼诺现象有关的向北平流相吻合。这种轶事关联激发了许多假设，但没有一个假设得到明确和令人信服的支持。受2015-2019 年空前数量的P. planipes搁浅和海上观测的推动，我们编制了 10 P. planipes数据集跨越 1950 年至 2019 年，使用 1981 年至 2010 年的传输分析测试了异常平流假设，并探索了其他令人信服的假设。我们发现加利福尼亚中部附近的P. planipes 的存在与墨西哥水域的异常平流有关，有时但并不总是与厄尔尼诺事件有关，P. planipes可能会在没有额外异常运输的情况下继续居住在北部水域数年，但可能受到以下因素的促进温暖的水域。通过确定偶发性P. planipes范围扩展背后的机制，我们表明源水指数可以为未来的异常事件提供早期指标。