National Marine Information and Research Centre, PO Box 912, Swakopmund, Namibia.
National Centers for Coastal Ocean Science, NOAA/National Ocean Service, Charleston, SC, 29412, USA.
Harmful Algae. 2018 May;75:118-128. doi: 10.1016/j.hal.2018.04.008. Epub 2018 May 3.
The Benguela upwelling system, considered the world's most productive marine ecosystem, has a long record of potentially toxic diatoms belonging to the genus Pseudo-nitzschia. Species of Pseudo-nitzschia were reported as early as 1936 from the northern Benguela upwelling system (nBUS). For the current study, long-term phytoplankton monitoring data (2004-2011) for the Namibian coast were analysed to examine inshore and offshore temporal distribution of Pseudo-nitzschia species, their diversity and ultrastructure. The potentially toxigenic P. pungens and P. australis were the dominant inshore species, whereas offshore Pseudo-nitzschia showed a higher diversity that also included potentially toxic species. During a warming event, a community shift from P. pungens and P. australis dominance to P. fraudulenta and P. multiseries was documented in the central nBUS. A case study of a toxic event (August 2004) revealed that P. australis and P. pungens were present at multiple inshore and offshore stations, coincident with fish (pilchard) and bird mortalities reported from the central part of Namibia. Toxin analyses (LC-MS/MS) of samples collected from June to August 2004 revealed the presence of particulate domoic acid (DA) in seawater at multiple stations (maximum ∼180 ng DA/L) in the >0.45 μm size-fraction, as well as detectable DA (0.12 μg DA/g) in the gut of one of two pilchard samples tested. These findings indicate that DA may have been associated with the fish and bird mortalities reported from this event in the nBUS. However, the co-occurrence of very high biomass phytoplankton blooms suggests that other explanations may be possible.
本格拉上升流系统被认为是世界上生产力最高的海洋生态系统，长期以来一直存在属于拟菱形藻属的潜在有毒硅藻。早在 1936 年，就有报道称在北本格拉上升流系统（nBUS）发现了拟菱形藻属的物种。在当前的研究中，对纳米比亚沿海地区的长期浮游植物监测数据（2004-2011 年）进行了分析，以检查近岸和近海的拟菱形藻属物种的时间分布、多样性和超微结构。具有潜在毒性的 P. pungens 和 P. australis 是近岸优势种，而近海拟菱形藻属的物种多样性更高，其中还包括具有潜在毒性的物种。在一次升温事件中，在 nBUS 中部记录到了从 P. pungens 和 P. australis 优势种向 P. fraudulenta 和 P. multiseries 的群落转移。一个有毒事件（2004 年 8 月）的案例研究表明，P. australis 和 P. pungens 同时存在于纳米比亚中部多个近岸和近海站，与鱼类（沙丁鱼）和鸟类死亡事件同时发生。对 2004 年 6 月至 8 月采集的样本进行的毒素分析（LC-MS/MS）显示，在多个站位的海水（>0.45μm 粒径）中存在颗粒状的软骨藻酸（DA）（最高达 180ng DA/L），以及在测试的两个沙丁鱼样本之一的肠道中检测到可检出的 DA（0.12μg DA/g）。这些发现表明，DA 可能与该事件中 nBUS 报道的鱼类和鸟类死亡事件有关。然而，极高生物量浮游植物大量繁殖的同时发生表明，可能还有其他解释。
