Biodiversity assessment of coastal lagoon through eDNA metabarcoding

Mediterranean coastal lagoons are environmentally important ecosystems whose conservation has been challenged due to anthropogenic impacts that promoted the expansion of non-indigenous and, sometimes, invasive species. Therefore, it is crucial to inventory biodiversity in these areas for the development of strategies of conservation and management. Classic methods used for biodiversity surveys and detection of non-native species may be unsuccessful for the detection and identification of species in early development stages, cryptic, microscopic, elusive and new coming species at low population density. The development of metabarcoding techniques in the last decade offers new opportunities for reliable biodiversity surveillance and facilitates early detection of nuisance species. The objective of this study was to analyse the species occurring in the protected coastal lagoon Canet-Saint Nazaire where environmental DNA (eDNA) were extracted from water samples, employing molecular and bioinformatic tools. Three replicates were taken in the proximity of the canal that connect the lagoon with the open sea. 27 OTUs were identified, corresponding 10 of them to Class Dinophyceae and other 17 correspond to Class Hexanuplia, Polychaeta, Bacillariophyceae and Eurotatoria. Results revealed the occurrence of several invasive species (Polydora cornuta and Acartia tonsa), organisms typical of polluted areas (Polydora cornuta and Capitella capitata), and algae that produce Harmful Algal Blooms (HABs), altogether proving the poor conservation status of the lagoon despite being under protection. The combined results demonstrate the importance of eDNA as an ecological warning system and suggest the need for detailed inventories in this lagoon.

地中海沿海泻湖是兼具重要生态服务功能的生态系统，其保护工作因人类活动推动外来（偶为入侵）物种扩散而面临严峻挑战。因此，对该类区域开展生物多样性清查，对于制定科学的保护与管理策略至关重要。传统的生物多样性调查及外来物种检测方法，往往难以有效检测和鉴定处于早期发育阶段的物种、隐蔽类群、微型生物、隐匿难测物种，以及种群密度较低的新出现物种。近十年间发展起来的宏条形码（metabarcoding）技术，为可靠的生物多样性监测提供了全新机遇，同时也助力有害物种的早期检测工作。本研究以受保护的沿海泻湖卡内-圣纳泽尔（Canet-Saint Nazaire）为研究区域，通过分子与生物信息学工具，对从水样中提取的环境DNA（environmental DNA, eDNA）所对应的物种展开分析。研究人员在连接该泻湖与外海的运河附近设置了三次重复采样。本次研究共鉴定出27个操作分类单元（Operational Taxonomic Unit, OTUs），其中10个隶属于甲藻纲（Dinophyceae），剩余17个分别隶属于六颚亚纲（Hexanuplia）、多毛纲（Polychaeta）、硅藻纲（Bacillariophyceae）以及真轮虫纲（Eurotatoria）。研究结果显示，该区域存在多种入侵物种（*Polydora cornuta*与*Acartia tonsa*）、污染生境典型物种（*Polydora cornuta*及*Capitella capitata*），以及可引发有害藻华（Harmful Algal Blooms, HABs）的藻类。上述结果充分表明，尽管该泻湖处于保护状态，但其生态保护现状依旧不容乐观。综合本研究的全部结果，证实了eDNA作为生态预警系统的重要价值，同时也提示我们需对该泻湖开展更为细致全面的生物多样性清查工作。