Marine phytomyxids represent often overlooked obligate biotrophic parasites colonizing diatoms, brown algae, and seagrasses. An illustrative example of their enigmatic nature is the phytomyxid infecting the seagrass Halophila stipulacea (a well-known Lessepsian migrant from the Indo-Pacific to the Mediterranean Sea). In the Mediterranean, the occurrence of this phytomyxid was first described in 1995 in the Strait of Messina (southern Italy) and the second time in 2017 in the Aegean coast of Turkey. Here we investigated, using scuba diving, stereomicroscopy, light and scanning electron microscopy, and molecular methods, whether the symbiosis is still present in southern Italy, its distribution in this region and its relation to the previous reports. From the total of 16 localities investigated, the symbiosis has only been found at one site. A seasonal pattern was observed with exceptionally high abundance (> 40% of the leaf petioles colonized) in September 2017, absence of the symbiosis in May/June 2018, and then again high infection rates (~ 30%) in September 2018. In terms of anatomy and morphology as well as resting spore dimensions and arrangement, the symbiosis seems to be identical to the preceding observations in the Mediterranean. According to the phylogenetic analyses of the 18S rRNA gene, the phytomyxid represents the first characterized member of the environmental clade "TAGIRI-5". Our results provide new clues about its on-site ecology (incl. possible dispersal mechanisms), hint that it is rare but established in the Mediterranean, and encourage further research into its distribution, ecophysiology, and taxonomy.

中文翻译：

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外来海草嗜盐菌的神秘性体寄生虫寄生虫：对其生态学，系统发育和在地中海中分布的新见解。

海洋疫霉菌是经常被忽视的专性生物营养性寄生虫，遍布硅藻，褐藻和海草。它们的神秘性质的一个说明性例子是感染了海草的嗜盐藻（Halophila stipulacea）（从印度太平洋到地中海的著名的勒比斯移民）。在地中海地区，这种phyxyyyidid的发生最早是在1995年在墨西拿海峡（意大利南部）中描述的，而在2017年第二次在土耳其爱琴海海岸中进行了描述。在这里，我们使用水肺潜水，体视显微镜，光和扫描电子显微镜以及分子方法研究了共生在意大利南部是否仍然存在，其在该地区的分布及其与先前报道的关系。在总共调查的16个地区中，仅在一处发现了这种共生。在2017年9月观察到一个季节性模式，其丰度非常高（>定植的叶柄的40％），在2018年5月/ 6月没有共生，然后在2018年9月再次很高的感染率（〜30％）。在解剖学和形态学以及静止孢子的大小和排列方式方面，共生似乎与地中海地区先前的观察相同。根据对18S rRNA基因的系统发育分析，phytyyxid代表环境进化枝“ TAGIRI-5”的第一个特征成员。我们的研究结果提供了有关其现场生态学的新线索（包括可能的扩散机制），暗示它很少见但在地中海地区已经建立，并鼓励对其分布，生态生理学和分类学进行进一步研究。