Pseudo-nitzschia australis (Frenguelli), a toxigenic pennate diatom capable of producing the neurotoxin domoic acid (DA), was examined in unialgal laboratory cultures to quantify its physiological response to ocean acidification (OA) - the decline in pH resulting from increasing partial pressure of CO₂ (pCO₂) in the oceans. Toxic blooms of P. australis are common in the coastal waters of eastern boundary upwelling systems (EBUS), including those of the California Current System (CCS) off the west coast of the United States where increased pCO₂ and decreased seawater pH are well-known. This study determined the production of dissolved (dDA) and particulate DA (pDA), the rates of growth and nutrient (nitrate, silicate and phosphate) utilization, cellular elemental ratios of carbon and nitrogen, and the photosynthetic response to declining pH during the exponential and stationary growth phases of a strain of P. australis isolated during a massive toxic bloom that persisted for months along much of the U.S. west coast during 2015. Our controlled lab studies showed that DA production significantly increased as pCO₂ increased, and total DA (pDA + dDA) normalized to cell density was 2.7 fold greater at pH 7.8 compared to pH 8.1 (control) during nutrient-limited stationary growth. However, exponential growth rates did not increase with declining pH, but remained constant until pH of 7.8 was reached, and then specific growth rates declined by ca. 30%. The toxin results demonstrate that despite minimal effects of OA observed during the nutrient-replete exponential growth phase, the enhancement of DA production, notably the 3-fold increase in particulate DA per cell, with declining pH from 8.1 to 7.8 during the nutrient-depleted stationary phase, supports the hypothesis that increasing pCO₂ will result in greater toxic risk to coastal ecosystems from elevated ambient concentrations of particulate DA. The ecological consequences of decreasing silicate uptake rates and increasing cellular carbon quotas with declining pH may potentially ameliorate some negative impacts of OA on Pseudo-nitzschia growth in natural systems.

Pseudo- nitzschia australis (Frenguelli) 是一种能够产生神经毒素软骨藻酸 (DA) 的产毒羽状硅藻，在单藻实验室培养物中进行了检查，以量化其对海洋酸化 (OA) 的生理反应 - 由于分压增加导致 pH 值下降海洋中的 CO ₂ ( p CO ₂ )。P. australis 的有毒水华在东部边界上升流系统 (EBUS) 的沿海水域中很常见，其中包括美国西海岸附近的加利福尼亚洋流系统 (CCS)，其中p CO ₂增加和降低海水 pH 值是众所周知的。该研究确定了溶解 (dDA) 和颗粒 DA (pDA) 的产生、生长速度和养分（硝酸盐、硅酸盐和磷酸盐）利用速度、碳和氮的细胞元素比率，以及指数期间对 pH 值下降的光合反应。2015 年在美国西海岸大部分地区持续数月的大规模有毒水华期间分离出的一株P. australis和稳定生长期。我们的受控实验室研究表明，随着p CO ₂在营养有限的静止生长期间，总 DA (pDA + dDA) 在 pH 7.8 时比 pH 8.1（对照）高 2.7 倍。然而，指数增长率并没有随着 pH 值的下降而增加，而是保持不变，直到 pH 值达到 7.8，然后比增长率下降了大约。30%。毒素结果表明，尽管在营养充足的指数生长期观察到 OA 的影响很小，但 DA 产量的增加，特别是每个细胞的颗粒 DA 增加了 3 倍，在营养耗尽期间 pH 从 8.1 下降到 7.8固定相，支持增加p CO ₂的假设环境中颗粒物 DA 浓度升高，将对沿海生态系统造成更大的毒性风险。随着 pH 值下降，降低硅酸盐吸收率和增加细胞碳配额的生态后果可能会改善 OA 对自然系统中假尼茨奇亚生长的一些负面影响。