Microbiome network in the pelagic and benthic offshore systems of the northern Adriatic Sea (Mediterranean Sea)

Background Because of their recognized global importance, there is now the urgent need to map diversity and distribution patterns of marine microbial communities. Even if available studies provided some advances in the understanding the biogeographical patterns of marine microbiomes at the global scale, their degree of plasticity at the local scale it is still underexplored, and functional implications still need to be dissected. In this scenario here we provide a synoptical study on the microbiomes of the water column and surface sediments from 19 sites in a 130 km2 area located 13.5 Km afar from the coast in the North-Western Adriatic Sea (Italy), providing the finest-scale mapping of marine microbiomes in the Mediterranean sea. Results Pelagic and benthic microbiomes in the study area showed sector specific-patterns and distinct assemblage structures, corresponding to specific variations in the microbiome network structure. While maintaining a balanced structure in term of provided ecosystem services (e.g., hydrocarbon degradation and nutrient cycling), sector-specific patterns of over-abundant modules - and taxa - were defined, with the South sector (the closest to the coast) characterized by microbial groups of terrestrial origins, both in the pelagic and the benthic realms. Conclusions By the granular assessment of the marine microbiome changes at the local scale, we have been able to highlight the admission of terrestrial microorganisms in the marine microbiome networks, as a possible natural process characterizing eutrophic coastal area. This raises the question about the biological threshold for terrestrial microorganisms to be admitted in the marine microbiome networks, without disturbing the ecological balance.

研究背景 鉴于海洋微生物群落的全球重要性已得到广泛认可，当前亟需绘制其多样性与分布格局图谱。尽管现有研究已在全球尺度上推进了对海洋微生物组（microbiome）生物地理格局的认知，但海洋微生物组在局域尺度下的可塑性程度仍未得到充分探索，其功能内涵亦有待进一步解析。在此背景下，本研究针对意大利西北亚得里亚海距岸13.5公里、面积130平方公里海域内的19个采样点，开展了水柱与表层沉积物微生物组的综合分析研究，完成了地中海海域最高分辨率的海洋微生物组分布图谱绘制。

研究结果 本研究区域的浮游（pelagic）与底栖（benthic）微生物组呈现出分区特异性分布格局与独特的群落组成结构，且与微生物组网络结构的特定变化相对应。研究区域的微生物组网络在维持生态系统服务功能（如烃类降解与营养盐循环）平衡的前提下，形成了分区特有的高丰度网络模块与微生物类群模式；其中距海岸最近的南部区域，无论浮游还是底栖生境，均以陆生起源的微生物类群为核心特征。

研究结论 本研究通过对海洋微生物组局域尺度变化的精细化解析，揭示了陆生微生物进入海洋微生物组网络这一过程，该过程可能是富营养化沿海海域的自然生态特征。这一发现提出了一个科学问题：陆生微生物进入海洋微生物组网络且不破坏生态平衡的生物学阈值究竟为何？