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

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.

本研究通过室内培养与生态系统实验，探究了沿岸酸化（coastal acidification）对产石房蛤毒素（saxitoxin）的甲藻（dinoflagellate）——芬迪湾亚历山大藻（Alexandrium fundyense）的生长与产毒特性的影响。在室内培养实验中，从美国纽约北港湾（Northport Bay）与加拿大芬迪湾（Bay of Fundy）分离得到的亚历山大藻（Alexandrium）菌株，在暴露于升高的二氧化碳分压（PCO2，90~190 Pa，即900~1900 µatm）环境时，其生长速率较40 Pa（即400 µatm）的对照组显著提升16%~190%（p<0.05）。高二氧化碳分压环境还使北港湾菌株的细胞总毒素含量（以fg石房蛤毒素当量/细胞计）显著增加71%~81%，但芬迪湾菌株的毒素含量未出现显著变化。二氧化碳分压升高与藻细胞生长提速之间的正相关关系，在纽约海域的天然亚历山大藻种群中得到了重复验证。将天然亚历山大藻种群置于150 Pa二氧化碳分压环境中培养时，其细胞密度相较于39 Pa组显著且持续升高。在北港湾天然亚历山大藻水华暴发期间，水体二氧化碳分压随水华进程升高至170 Pa以上，且在藻细胞丰度最高的区域，二氧化碳分压达到峰值，这表明亚历山大藻可能进一步加剧沿岸酸化，或其本身已特别适应此类酸化环境。亚历山大藻水华与二氧化碳分压升高的共同发生，代表了一种此前未被认知的、会加重沿海生态系统环境风险的复合威胁。高二氧化碳分压可提升亚历山大藻的生长速率与毒素产量，这表明富营养化（eutrophication）或气候变化（climate change）驱动的沿岸酸化，可能会加剧此类以及其他有害藻华（harmful algal blooms）的暴发。