Table_1_Metabarcoding reveals a high diversity and complex eukaryotic microalgal community in coastal waters of the northern Beibu Gulf, China.xlsx

Beibu Gulf is an important semi-enclosed bay located in the northwestern South China Sea, and is famous for its high bio-productivity and rich bio-diversity. The fast development along the Beibu Gulf Economical Rim has brought pressure to the environment, and algal blooms occurred frequently in the gulf. In this study, surface water samples and micro-plankton samples (20–200 μm) were collected in the northern Beibu Gulf coast. Diversity and distribution of eukaryotic planktonic microalgae were analyzed by both metabarcoding and microscopic analyses. Metabarcoding revealed much higher diversity and species richness of microalgae than morphological observation, especially for dinoflagellates. Metabarcoding detected 144 microalgal genera in 8 phyla, while microscopy only detected 40 genera in 2 phyla. The two methods revealed different microalgal community structures. Dinoflagellates dominated in microalgal community based on metabarcoding due to their high copies of 18 s rRNA gene, and diatoms dominated under microscopy. Altogether 48 algal bloom and/or toxic species were detected in this study, 34 species by metabarcoding and 19 species by microscopy. Our result suggested a high potential risk of HABs in the Beibu Gulf. Microalgal community in the surface water samples demonstrated significantly higher OTU/species richness, alpha diversity, and abundance than those in the micro-plankton samples, although more HAB taxa were detected by microscopic observations in the micro-plankton samples. Furthermore, nano-sized taxa, such as those in chlorophytes, haptophytes, and chrysophyceans, occurred more abundantly in the surface water samples. This study provided a comprehensive morphological and molecular description of microalgal community in the northern Beibu Gulf.

北部湾，位于中国南海西北部的一个重要的半封闭海湾，以其高生物生产力和丰富的生物多样性而闻名。北部湾经济圈的高速发展对环境造成了压力，海湾内频繁发生藻华现象。在本研究中，于北部湾海岸采集了表层水体样本和微型浮游生物样本（直径20-200微米）。通过对真核浮游微型藻类的多样性和分布进行元条形码和显微镜分析，探讨了其多样性。元条形码揭示了比形态学观察更高的微型藻类多样性和物种丰富度，尤其是在隐藻类中。元条形码检测到8个门类中的144个微型藻类属，而显微镜仅检测到2个门类中的40个属。两种方法揭示了不同的微型藻类群落结构。基于元条形码，由于18S rRNA基因的高拷贝数，隐藻类在微型藻类群落中占主导地位，而硅藻在显微镜下占主导地位。本研究共检测到48种藻华和/或有毒物种，其中34种通过元条形码检测，19种通过显微镜检测。我们的结果表明，北部湾存在高潜在风险的红潮。表层水体样本中的微型藻类群落显示出比微型浮游生物样本中显著更高的操作分类单元/物种丰富度、α多样性和丰度，尽管在微型浮游生物样本中通过显微镜观察到的红潮类群更多。此外，纳米级类群，如绿藻、黄藻和金藻等，在表层水体样本中更为丰富。本研究对北部湾北部微型藻类群落进行了全面的形态学和分子描述。