Enrichment of the oceans with CO₂ may be beneficial for some marine phytoplankton, including harmful algae. Numerous laboratory experiments provided valuable insights into the effects of elevated pCO₂ on the growth and physiology of harmful algal species, including the production of phycotoxins. Experiments close to natural conditions are the next step to improve predictions, as they consider the complex interplay between biotic and abiotic factors that can confound the direct effects of ocean acidification. We therefore investigated the effect of ocean acidification on the occurrence and abundance of phycotoxins in bulk plankton samples during a long-term mesocosm experiment in the Gullmar Fjord, Sweden, an area frequently experiencing harmful algal blooms. During the experimental period, a total of seven phycotoxin-producing harmful algal genera were identified in the fjord, and in accordance, six toxin classes were detected. However, within the mesocosms, only domoic acid and the corresponding producer Pseudo-nitzschia spp. was observed. Despite high variation within treatments, significantly higher particulate domoic acid contents were measured in the mesocosms with elevated pCO₂. Higher particulate domoic acid contents were additionally associated with macronutrient limitation. The risks associated with potentially higher phycotoxin levels in the future ocean warrants attention and should be considered in prospective monitoring strategies for coastal marine waters.

用CO ₂富集海洋对于某些海洋浮游植物（包括有害藻类）可能是有益的。大量的实验室实验为pCO ₂升高的影响提供了有价值的见解。对有害藻类的生长和生理的影响，包括藻毒素的产生。接近自然条件的实验是改善预测的下一步，因为它们考虑了生物和非生物因素之间的复杂相互作用，这些相互作用会混淆海洋酸化的直接影响。因此，在瑞典古尔玛峡湾（Gullmar Fjord）的长期中观试验中，我们研究了海洋酸化对大量浮游生物样品中藻毒素的发生和丰度的影响，该地区经常发生有害的藻华。在实验期间，在峡湾中总共鉴定出7种产生植物毒素的有害藻类，并相应地检测到6种毒素。但是，在中膜范围内，只有十二烷酸和相应的生产者拟南芥属。被观测到。尽管治疗之间存在很大差异，但在pCO ₂升高的中膜中仍测得明显更高的颗粒状海藻酸含量。较高的颗粒状二氢酸含量还与大量营养素缺乏有关。与未来海洋中潜在更高的植物毒素水平相关的风险值得关注，应在沿海海洋水域的前瞻性监测策略中予以考虑。