Marine impactful cryptogenic and alien species in the Greek Seas: A georeferenced dataset (1893-2020)

The GreekMarineICAS geodataset was created as part of the project ALAS: Aliens in the Aegean – A Sea Under Siege project (https://alas.edu.gr/), with the aim to assess the spatial extent and potential impacts of alien species in the Aegean Sea, and to improve our understanding of the mechanisms driving the impacts of invasive alien species on native marine ecosystems. Methodology of data compilation: Initially, an ICAS catalogue was created, including species classified as of high impact in the European Alien Species Information Network (EASIN), or as invasive or of high impact in recent review papers. A thorough search was conducted to look for information on the presence of these species in the Greek Seas. Georeferenced data, along with information on the reported date / year of sighting, depth range, abundance and habitat type were compiled using all available types of data sources, including published scientific literature, grey literature (e.g., theses, technical reports, and newspaper reports), offline databases (including records from past projects of universities, research institutes, the ELNAIS database, and citizen science initiatives), online scientific or citizen science databases (Algaebase, GBIF, OBIS, iNaturalist - only research-grade data), social networks (e.g., Instagram and Facebook), as well as through field work involving scientific diving and interviews with marine scientists, fishers and divers that were carried out during the ALAS project. In situ underwater sampling during the ALAS project was carried out in 2020 at 156 sites, and all sampling was conducted using non-destructive visual sampling techniques via SCUBA or free diving, down to a maximum of 20 m depth. Moreover, an unstructured interview approach was applied during the respective interviews with marine scientists, fishers and divers, while a photographic guide of the targeted ICAS was produced and provided during the interviews to enhance the species verification process. Information from social networks was specifically retrieved from the websites of diving centers, which were thoroughly checked for images of ICAS, and once relevant images were found the corresponding information was further validated through direct communication. All data were organized within an Excel spreadsheet and all duplicate records were deleted.

GreekMarineICAS地理数据集是作为ALAS项目：“爱琴海的外来物种——受困之海”（https://alas.edu.gr/）的一部分构建而成，旨在评估爱琴海外来物种的空间分布范围与潜在影响，加深我们对入侵外来物种对本土海洋生态系统影响机制的理解。

数据编纂方法如下：首先，构建了ICAS名录，收录了欧洲外来物种信息网络（European Alien Species Information Network，EASIN）中被列为高影响的物种，以及近期综述文献中被认定为入侵物种或高影响类群的物种。随后开展了全面调研，检索希腊海域内上述物种的存在相关信息。

研究团队整合了所有可用数据源的地理参考数据，以及目击报告的日期/年份、深度范围、物种丰度和栖息地类型等信息。可用数据源涵盖已发表的科学文献、灰色文献（如学位论文、技术报告、新闻报道）、离线数据库（包含大学、科研机构过往项目的记录、ELNAIS数据库以及公民科学项目数据）、在线科学或公民科学数据库（Algaebase、GBIF、OBIS、iNaturalist——仅研究级数据）、社交网络平台（如Instagram、Facebook）；同时依托ALAS项目期间开展的科学潜水调研，以及对海洋科学家、渔民和潜水员的访谈获取数据。

ALAS项目于2020年在156个采样点开展了原位水下采样，所有采样均采用非破坏性视觉采样技术，通过水肺潜水（SCUBA）或自由潜水完成，最大采样深度达20米。此外，在对海洋科学家、渔民和潜水员的访谈中采用了非结构化访谈方法，同时编制并在访谈中提供了针对目标ICAS的影像图鉴，以提升物种核验的准确性。

社交网络相关数据专门从潜水中心网站获取，研究人员逐一排查其中的ICAS相关影像，一旦发现符合条件的图片，将通过直接沟通进一步验证对应信息的真实性。所有数据均整理至Excel电子表格中，并删除了重复记录。