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Harmful algal blooms of Heterosigma akashiwo and environmental features regulate Mesodinium cf. rubrum abundance in eutrophic conditions
Harmful Algae ( IF 6.6 ) Pub Date : 2020-11-12 , DOI: 10.1016/j.hal.2020.101943
Daniel A. Lemley , Janine B. Adams , Gavin M. Rishworth , Duncan A. Purdie

Functional drivers of phytoplankton that can potentially form harmful algal blooms (HABs) are important to understand given the increased prevalence of anthropogenic modification and pressure on coastal habitats. However, teasing these drivers apart from other influences is problematic in natural systems, while laboratory assessments often fail to replicate relevant natural conditions. One such potential bloom-forming species complex highlighted globally is Mesodinium cf. rubrum, a planktonic ciliate. This species occurs persistently in the Sundays Estuary in South Africa yet has never been observed to “bloom” (> 1,000 cell.ml−1). Modified by artificial nutrient-rich baseflow conditions, the Sundays Estuary provides a unique Southern Hemisphere case study to identify the autecological drivers of this ciliate due to artificial seasonally “controlled” abiotic environmental conditions. This study utilised a three-year monitoring dataset (899 samples) to assess the drivers of M. cf. rubrum using a generalised modelling approach. Key abiotic variables that influenced population abundance were season and salinity, with M. cf. rubrum populations peaking in summer and spring and preferring polyhaline salinity regions (>18) with pronounced water column salinity stratification, especially in warmer months. This was reflected in the diel vertical migration (DVM) behaviour of this species, demonstrating its ability to utilise the optimal daylight photosynthetic surface conditions and high-nutrient bottom waters at night. The only phytoplankton groups clearly associated with M. cf. rubrum were Raphidophyceae and Cryptophyceae. Although M. cf. rubrum reflects a niche overlap with the dominant HAB-forming phytoplankton in the estuary (the raphidophyte, Heterosigma akashiwo), its reduced competitive abilities restrict its abundance. In contrast, the mixotrophic foraging behaviour of M. cf. rubrum exerts a top-down control on cryptophyte prey abundance, yet, the limited availability of these prey resources (mean < 300 cells ml−1) seemingly inhibits the formation of red-water accumulations. Hydrodynamic variability is necessary to ensure that no single phytoplankton HAB-forming taxa outcompetes the rest. These results confirm aspects of the autecology of M. cf. rubrum related to salinity associations and DVM behaviour and contribute to a global understanding of managing HABs in estuaries.



中文翻译:

赤潮异弯藻和环境功能调节中缢比照 富营养条件下的红细胞丰度

考虑到人为改变的普遍性和沿海生境压力的增加,有可能形成有害藻华(HAB)的浮游植物功能驱动因素非常重要。然而,在自然系统中,除其他因素外,将这些驱动因素分开是有问题的,而实验室评估通常无法复制相关的自然条件。Mesodinium cf是全球关注的潜在此类形成花开的物种复合体。rubrum,浮游纤毛虫。该种持续存在于南非的周日河口,但从未观察到“开花”(> 1,000 cell.ml -1)。通过人工富含营养的基础水流条件,周日河口提供了一个独特的南半球案例研究,以识别由于人工季节性“受控”非生物环境条件而导致该纤毛虫的病因。这项研究利用了一个为期三年的监测数据集(899个样本)来评估M. cf.的驱动因素rubrum使用通用建模方法。主要非生物变量的影响种群数量分别为季节和盐度,与M.风疹种群在夏季和春季达到顶峰,并倾向于水盐盐度分层明显的多盐度盐度区域(> 18),尤其是在温暖的月份。这反映在该物种的diel垂直迁移(DVM)行为中,表明其具有利用最佳日光光合表面条件和夜间高营养底水的能力。唯一的浮游植物明确的与M.风铃草有菊科和隐藻科。虽然M.风疹反映出与河口占主导地位的形成HAB的浮游植物的生态位重叠(水生植物,杂藻赤潮),竞争能力的下降限制了其丰富度。相比之下,的混合营养觅食行为M.rubrum对自生植物的猎物丰富度进行了自上而下的控制,但是,这些猎物资源的有限可用性(平均<300个细胞ml -1)似乎抑制了红水积聚的形成。为了确保没有单个浮游植物HAB形成的类群能胜过其他种类,水动力可变性是必要的。这些结果证实的个体生态学方面M.rubrum与盐度协会和DVM行为有关,有助于全球了解河口HAB的管理。

更新日期:2020-12-07
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