School of Life Sciences, University of Technology Sydney, PO Box 123, Broadway, NSW, 2000, Australia.
NSW Department of Primary Industries, Narrandera Fisheries Centre, PO Box 182, Narrandera, New South Wales, 2700, Australia.
Harmful Algae. 2022 Aug;117:102284. doi: 10.1016/j.hal.2022.102284. Epub 2022 Jul 6.
Cyanobacterial blooms have major impacts on the ecological integrity and anthropogenic value of freshwater systems. Chrysosporum ovalisporum, a potentially toxic cyanobacteria has been rare in Australian waters until recently when is has bloomed in a number of lake and river systems. The aim of this study was to determine drivers of its growth and growing dominance. We performed regular monitoring of Mannus Lake, a small freshwater reservoir in South-Eastern Australia that has recently undergone extremely dense bloom events. Blooms of the diazotrophic Chrysosporum ovalisporum occurred in both summers of the 19 month study during periods of persistent thermal stratification. Following the C. ovalisporum blooms, non-diazotrophic taxa (Microcystis aeruginosa and Woronichinia sp.) dominated the phytoplankton community under less stratified conditions. Thermal stratification and nitrogen availability appeared to be the primary drivers of changes in cyanobacterial community structure. We propose that the observed transition from C. ovalisporum to M. aeruginosa and/or Woronichinia sp. may be a result of nitrogen limitation in early summer, which combined with persistent thermal stratification led to an ecological advantage for the nitrogen-fixing C. ovalisporum. Mixing events caused the senescence of the C. ovalisporum bloom, likely supplementing the nutrient budget of the lake with atmospherically derived N and alleviating N limitation to non-diazotrophic taxa. Non-diazotrophic cyanobacterial growth then increased, albeit at much lower biovolumes compared to the initial bloom. Overall, the results demonstrate the role of thermal stratification and nutrient cycling in structuring the cyanobacterial community and provide insights into the environmental factors driving the proliferation of the relatively new, potentially toxic cyanobacterium C. ovalisporum in Australian waters.
蓝藻水华对淡水系统的生态完整性和人为价值有重大影响。Chrysosporum ovalisporum 是一种潜在的有毒蓝藻，直到最近才在澳大利亚水域大量繁殖，出现在许多湖泊和河流系统中。本研究的目的是确定其生长和优势增长的驱动因素。我们对澳大利亚东南部一个小型淡水水库曼努斯湖进行了定期监测，该湖最近发生了极其密集的水华事件。在 19 个月的研究中，两个夏季都出现了固氮的 Chrysosporum ovalisporum 水华，期间持续存在热分层现象。在 Chrysosporum ovalisporum 水华之后，在分层较少的情况下，非固氮类群（铜绿微囊藻和沃隆宁希亚属）占据了浮游植物群落的主导地位。热分层和氮供应似乎是蓝藻群落结构变化的主要驱动因素。我们提出，观察到从 Chrysosporum ovalisporum 到 M. aeruginosa 和/或 Woronichinia sp. 的转变可能是由于初夏氮限制，加上持续的热分层，导致具有固氮能力的 Chrysosporum ovalisporum 具有生态优势。混合事件导致 Chrysosporum ovalisporum 水华衰老，可能通过大气来源的 N 补充湖泊的养分预算，并缓解非固氮类群的氮限制。然后，非固氮蓝藻的生长增加，尽管与最初的水华相比，生物量要低得多。总的来说，结果表明了热分层和营养循环在构建蓝藻群落中的作用，并深入了解了驱动相对较新的潜在有毒蓝藻 Chrysosporum ovalisporum 在澳大利亚水域增殖的环境因素。
