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Abstract：
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.
摘要：
北部湾是南中国海西北部重要的半封闭海湾,并以其高生物生产力和丰富的生物多样性而闻名。北部湾经济圈的快速发展给环境带来了压力,藻类在海湾频繁出现。在这项研究中,在北部湾北部海岸收集了地表水样品和微浮游生物样品（20-200μm）。通过代谢编码和微观分析分析了真核浮游微藻的多样性和分布。代谢编码显示微藻的多样性和物种丰富度远高于形态学观察，尤其是对鞭毛藻.代谢编码在8个叶中检测到144个微藻属，而显微镜只检测到2门40属。两种方法揭示了不同的微藻群落结构。由于18srRNA基因的高拷贝，鞭毛虫在微藻群落中占主导地位。和硅藻在显微镜下占主导地位。在这项研究中总共检测到48种藻水华和/或有毒物种，34种通过metabarcoding和19种通过显微镜。我们的结果表明北部湾HAB的潜在风险很高。地表水样品中的微藻群落表现出明显更高的OTU/物种丰富度，阿尔法多样性，比微浮游生物样本中的丰度高，尽管通过微观观察在微浮游生物样品中检测到更多的HAB类群。此外，纳米大小的分类群，比如绿藻中的那些，haptophytes,和菊科植物，在地表水样品中发生得更多。这项研究提供了北部湾北部微藻群落的形态和分子描述。
