The potential for toxic contaminants and nutrient pollution to alter natural cycles of estuarine phytoplankton blooms is well known, yet few studies have examined how these combined stressors affect harmful algal species. Here, a robust testing protocol was developed to enable an ecotoxicological assessment of responses to commonly co-occurring estuarine contaminants by harmful algal bloom species. The population growth and toxicity (as cell density and hemolytic activity, respectively) of a cultured strain of the toxigenic raphidiophycean, Chattonella subsalsa, were assessed in two experiments (duration 10 days and 28 days) across a gradient of atrazine concentrations and N:P ratios simulating nutrient-rich versus nutrient-depleted regimes. The response of this large-celled, slowly growing alga to atrazine × nutrients depended on growth phase; atrazine was most inhibitory during early exponential population growth (day 10), whereas nutrient regime was a more important influence during later phases of growth (day 28). Without atrazine, toxicity toward fish was highest in low-P cultures. At atrazine levels >25 μg L⁻¹, hemolytic activity was highest in low-N cultures, and increased with increasing atrazine concentration in all nutrient-limited cultures. Hemolytic activity varied inversely with atrazine concentration in N,P-replete conditions. Overall, atrazine inhibitory effects on population growth of this C. subsalsa strain depended on the growth phase and the nutrient regime; hemolytic activity was higher and further enhanced by atrazine in low N-P regimes; and atrazine inhibited hemolytic activity in nutrient-replete conditions. The data suggest that, depending on the growth phase and nutrient regime, atrazine can help promote toxic C. subsalsa blooms.

众所周知，有毒污染物和营养物污染可能改变河口浮游植物开花的自然周期，但很少有研究检查这些综合压力源如何影响有害藻类。在这里，开发了一种强大的测试方案，可以对有害藻华物种对共同存在的河口污染物的反应进行生态毒理学评估。产毒的双歧藻类沙门氏菌的培养菌株的种群生长和毒性（分别为细胞密度和溶血活性）在两个实验（持续时间分别为10天和28天）中，通过模拟r富营养与富营养方案的at去津浓度和N：P比率的梯度，对进行了评估。这种大细胞，缓慢生长的藻类对at去津×营养物的反应取决于生长期；阿特拉津在早期指数种群增长（第10天）时具有最大的抑制作用，而养分制度在生长的后期阶段（第28天）具有更重要的影响。没有阿特拉津，在低磷养殖中对鱼类的毒性最高。阿特拉津水平> 25μgL ^-1，低氮培养物中的溶血活性最高，并且在所有营养受限的培养物中，随着阿特拉津浓度的增加而增加。在氮，磷充足的条件下，溶血活性与at去津浓度成反比。总体而言，阿特拉津对这株拟南芥C. subsalsa菌株种群生长的抑制作用取决于其生长期和养分状况。在低NP方案中，阿特拉津具有更高的溶血活性，并且进一步增强了溶血活性。和r去津在营养丰富的条件下抑制溶血活性。数据表明，根据生长期和养分状况，at去津可以帮助促进有毒的C. subsalsa绽放。