The effects of elevated CO2 on the growth and toxicity of field populations and cultures of the saxitoxin-producing dinoflagellate, Alexandrium fundyense

The effects of coastal acidification on the growth and toxicity of the saxitoxin-producing dinoflagellate Alexandrium fundyense were examined in culture and ecosystem studies. In culture experiments, Alexandrium strains isolated from Northport Bay, New York, and the Bay of Fundy, Canada, grew significantly faster (16-190%; p < 0.05) when exposed to elevated levels of PCO2 ( 90-190 Pa=900-1900 µatm) compared to lower levels ( 40 Pa=400 µatm). Exposure to higher levels of PCO2 also resulted in significant increases (71-81%) in total cellular toxicity (fg saxitoxin equivalents/cell) in the Northport Bay strain, while no changes in toxicity were detected in the Bay of Fundy strain. The positive relationship between PCO2 enrichment and elevated growth was reproducible in natural populations from New York waters. Alexandrium densities were significantly and consistently enhanced when natural populations were incubated at 150 Pa PCO2 compared to 39 Pa. During natural Alexandrium blooms in Northport Bay, PCO2 concentrations increased over the course of a bloom to more than 170 Pa and were highest in regions with the greatest Alexandrium abundances, suggesting Alexandrium may further exacerbate acidification and/or be especially adapted to these acidi-fied conditions. The co-occurrence of Alexandrium blooms and elevated PCO2 represents a previously unrecognized, compounding environmental threat to coastal ecosystems. The ability of elevated PCO2 to enhance the growth and toxicity of Alexandrium indicates that acidification promoted by eutrophication or climate change can intensify these, and perhaps other, harmful algal blooms.

本研究通过培养实验与生态系统研究，探究了海洋酸化对产石房蛤毒素（saxitoxin）的甲藻亚历山大藻（Alexandrium fundyense）的生长与产毒特性的影响。在培养实验中，从美国纽约北港湾与加拿大芬迪湾分离得到的亚历山大藻菌株，在高二氧化碳分压（PCO2，90~190 Pa=900~1900 µatm）环境下的生长速率显著高于低二氧化碳分压环境（40 Pa=400 µatm），增幅达16%~190%（p < 0.05）。高二氧化碳分压暴露还使北港湾菌株的细胞总毒素含量（以石房蛤毒素当量计，fg/细胞）显著提升71%~81%，而芬迪湾菌株的毒素含量未检测到显著变化。高二氧化碳分压富集与生长提升之间的正相关关系，在纽约海域的自然种群中得到了重复验证。当自然种群在150 Pa PCO2环境下培养时，其亚历山大藻细胞密度显著且持续高于39 Pa环境下的密度。在北港湾自然亚历山大藻藻华发生期间，藻华过程中PCO2浓度逐步升高至170 Pa以上，且在亚历山大藻丰度最高的区域浓度达到峰值，这表明亚历山大藻可能进一步加剧海洋酸化，或其本身已适应此类酸化环境。亚历山大藻藻华与高二氧化碳分压共存的现象，代表了一种此前未被认知的、加剧海岸生态系统威胁的复合环境压力。高二氧化碳分压可促进亚历山大藻的生长与产毒能力，这意味着富营养化或气候变化引发的海洋酸化，可能会加剧此类乃至其他有害藻华的暴发。