The Microcystis aeruginosa complex (MAC) clusters cosmopolitan and conspicuous harmful bloom-forming cyanobacteria able to produce cyanotoxins. It is hypothesized that low temperatures and brackish salinities are the main barriers to MAC proliferation. Here, patterns at multiple levels of organization irrespective of taxonomic identity (i.e. a trait-based approach) were analyzed. MAC responses from the intracellular (e.g. respiratory activity) to the ecosystem level (e.g. blooms) were evaluated in wide environmental gradients. Experimental results on buoyancy and respiratory activity in response to increased salinity (0–35) and a literature review of maximum growth rates under different temperatures and salinities were combined with field sampling from headwaters (800 km upstream) to the marine end of the Rio de la Plata estuary (Uruguay-South America). Salinity and temperature were the major variables affecting MAC responses. Experimentally, freshwater MAC cells remained active for 24 h in brackish waters (salinity = 15) while colonies increased their flotation velocity. At the population level, maximum growth rate decreased with salinity and presented a unimodal exponential response with temperature, showing an optimum at 27.5 °C and a rapid decrease thereafter. At the community and ecosystem levels, MAC occurred from fresh to marine waters (salinity 30) with a sustained relative increase of large mucilaginous colonies biovolume with respect to individual cells. Similarly, total biomass and, specific and morphological richness decreased with salinity while blooms were only detected in freshwater both at high (33 °C) and low (11 °C) temperatures. In brackish waters, large mucilaginous colonies presented advantages under osmotic restrictive conditions. These traits values have also been associated with higher toxicity potential. This suggest salinity or low temperatures would not represent effective barriers for the survival and transport of potentially toxic MAC under likely near future scenarios of increasing human impacts (i.e. eutrophication, dam construction and climate change).

的铜绿微囊藻复合物（MAC）的簇国际性和显眼有害华形成蓝藻能够生产藻毒素。假设低温和微咸盐度是MAC扩散的主要障碍。在这里，分析了组织的多个级别的模式，而与分类学身份（即基于特征的方法）无关。从细胞内（例如呼吸活动）到生态系统水平（例如，大花）在宽广的环境梯度中进行了评估。响应于盐度增加（0-35）的浮力和呼吸活动的实验结果以及在不同温度和盐度下最大生长速率的文献综述，结合从上游（上游800 km）到里约热内卢海域的野外采样拉普拉塔河口（乌拉圭-南美）。盐度和温度是影响MAC响应的主要变量。在实验中，淡水MAC细胞在微咸水（盐度= 15）中保持活跃24小时，而菌落则提高了它们的浮选速度。在人口水平上，最大增长率随着盐度的降低而下降，并呈现出随温度的单峰指数响应，在27.5°C时表现出最佳，随后迅速下降。在社区和生态系统层面，MAC从淡水到海水（盐度30）发生，相对于单个细胞而言，大的粘液菌落的生物量持续相对增加。同样，总生物量，比和形态丰富度随盐度而降低，而仅在高温（33°C）和低温（11°C）时才在淡水中检测到水华。在微咸水域中，大的粘液菌落在渗透限制条件下表现出优势。这些特性值还与更高的毒性潜能相关。这表明盐分或低温不会代表潜在的有毒MAC的生存和运输的有效障碍，这可能会在不久的将来增加人类影响的情况下发生（即富营养化，大坝建设和气候变化）。