Microcystins (MCs) are the most studied toxins of cyanobacteria in freshwater bodies worldwide. However, they are poorly documented in coastal waters in several parts of the world. In this study, we investigated the composition of cyanobacteria and the presence of microcystins (MCs) in several coastal aquatic ecosystems of Nigeria. Direct morphological analysis revealed that members of the genus Oscillatoria were dominant with five species, followed by Trichodesmium with two species in Nigerian coastal waters. Oso Ibanilo had the highest cyanobacterial biomass (998 × 10³ cells/L), followed by Rivers Ocean (156 × 10³ cells/L). Except for the Cross River Ocean, cyanobacteria were present in all the investigated aquatic ecosystems. Ten (10) out of twenty water bodies examined had detectable levels of MCs. Furthermore, genomic DNA analysis for the mcyE gene of microcystin synthetase (mcy) cluster showed identities higher than 86% (query coverage > 96%) with toxic strains of cyanobacteria in all the samples analyzed. Also, the sequences of samples matched those of uncultured cyanobacteria from recreational lakes in Southern Germany. Our findings indicate that the presence of toxic cyanobacteria in coastal waters of Nigeria is of public and environmental health concern.

微囊藻毒素 (MCs) 是全球淡水水体中研究最多的蓝藻毒素。然而，它们在世界一些地区的沿海水域中的记录很少。在这项研究中，我们调查了尼日利亚几个沿海水生生态系统中蓝藻的组成和微囊藻毒素 (MC) 的存在。直接形态学分析显示，在尼日利亚沿海水域，Oscillatoria属的成员占优势，有 5 种，其次是Trichodesmium，有 2 种。Oso Ibanilo 的蓝藻生物量最高（998 × 10 ^{3 个}细胞/L），其次是 Rivers Ocean（156 × 10 ³细胞/升）。除跨河海洋外，所有调查的水生生态系统中都存在蓝藻。检查的二十个水体中有十 (10) 个具有可检测水平的 MC。此外，对微囊藻毒素合成酶 ( mcy ) 簇的mcy E 基因的基因组 DNA 分析显示，在所有分析的样品中，与蓝藻有毒菌株的同一性高于 86%（查询覆盖率 > 96%）。此外，样本序列与来自德国南部休闲湖泊的未培养蓝藻的序列相匹配。我们的研究结果表明，尼日利亚沿海水域中有毒蓝藻的存在引起了公众和环境健康的关注。