Seagrasses and associated microbial communities constitute a functional unit (holobiont) which responds as a whole to environmental changes. However, it is still unclear how the microbial colonizers are selected. In this study we compared the epiphytic microbial communities associated with Posidonia oceanica and Halophila stipulacea, Mediterranean native and exotic seagrass species, respectively, growing side by side in monospecific patches within the port of Limassol (Cyprus, Eastern Mediterranean Sea). To evaluate whether the environment rather than the host species and/or its physiological condition play a role in shaping the seagrass epiphytic microbial community, the environmental microbial communities (seawater and sediment) and seagrass associated ones were determined by using 16S rRNA gene amplicon sequencing. Plant ecological status was evaluated by morphological (biometry), structural (density) and biochemical (pigment/phenol content) descriptors. In both species, leaf associated microbial communities are clearly similar to seawater microbes; conversely, microbes associated with H. stipulacea roots/rhizomes differ from the microbial communities in surrounding sediment. In both seagrasses, Pseudomonadaceae was the most abundant family on leaves, but each species harboured unique microbial families. To our best knowledge, this is the first study on these two neighbouring seagrass species, coupling plant ecological status with associated microbial communities. Results demonstrated that each seagrass responded differently to the same environmental conditions and selected different epiphytic microbial communities, supporting their putative use as ecological indicators.

海草和相关的微生物群落构成一个功能单元（holobiont），作为一个整体响应环境变化。然而，目前尚不清楚如何选择微生物定植者。在这项研究中，我们比较了与Posidonia oceanica和Halophila stipulacea相关的附生微生物群落，地中海本地和外来海草物种，分别在利马索尔港（塞浦路斯，东地中海）内以单一品种的斑块并排生长。为了评估环境而不是宿主物种和/或其生理条件是否在塑造海草附生微生物群落中起作用，通过使用 16S rRNA 基因扩增子测序确定环境微生物群落（海水和沉积物）和海草相关微生物群落。植物生态状况通过形态（生物计量学）、结构（密度）和生化（色素/酚含量）描述符进行评估。在这两个物种中，与叶片相关的微生物群落与海水微生物明显相似；相反，与H. stipulacea相关的微生物根/根茎与周围沉积物中的微生物群落不同。在这两种海草中，假单胞菌科是叶子上最丰富的家族，但每个物种都拥有独特的微生物家族。据我们所知，这是对这两种相邻海草物种的首次研究，将植物生态状况与相关微生物群落联系起来。结果表明，每种海草对相同环境条件的反应不同，并选择不同的附生微生物群落，支持它们作为生态指标的推定用途。