Alien species have invaded worldwide and altered native biodiversity and ecosystem functions. In Lake Biwa, Japan, Micrasterias hardyi—considered an endemic species in Australia—has become one of the major dominant species since 2016. To evaluate long-term and seasonal variations in M. hardyi, we analyzed 20 years of plankton samples from the northern basin of Lake Biwa. The presence of this species was first confirmed in February 2015, and increased for long periods from November 2015 (4.2 cells cm⁻²) to December 2016 (2.3 × 10⁵ cells cm⁻²) and from September 2017 (2.0 × 10² cells cm⁻²) to January 2019 (5.7 × 10⁴ cells cm⁻²). Particles similar to chytrid zoosporangia were observed and attached to M. hardyi cells. However, the infection rate was low (up to 22.5%), and the infection did not seem to be a major lethal factor. We estimated that M. hardyi was introduced in the early 2000s by simple linear regression of abundance. This result indicates the existence of long time lag from introduction to detection. Moreover, as the propagule pressure to nearby water systems has been high, it is highly probable that M. hardyi has spread to other lakes and ponds via Lake Biwa.

中文翻译：

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日本琵琶湖非原生性浮游植物Micrasterias hardyi（Zygnematophyceae，Streptophyta）丰度的长期变化

外来物种入侵了世界各地，改变了当地的生物多样性和生态系统功能。自2016年以来，在日本琵琶湖中，被认为是澳大利亚特有物种的哈氏微藻已经成为主要的优势物种之一。为了评估哈伊氏藻的长期和季节性变化，我们分析了北部20年的浮游生物样本。琵琶湖盆地。该物种的存在于2015年2月首次确认，并从2015年11月（4.2个细胞cm ^-2）到2016年12月（2.3×10 ^5个 细胞cm ^-2）和2017年9月（2.0×10 ^2个 细胞）长期增加cm ^-2）至2019年1月（5.7×10 ⁴ 单元cm^-2）。观察到类似于食糜菌孢子囊的颗粒，并附着于哈氏支原体细胞。但是，感染率很低（高达22.5％），而且感染似乎并不是主要的致死因素。我们估计通过简单的线性丰度线性回归，在2000年代初引入了哈迪木。该结果表明从引入到检测存在长时间的滞后。此外，由于对附近水系统的繁殖压力很高，因此哈迪氏菌很可能已通过琵琶湖扩散到其他湖泊和池塘。