Effect of acidification on an Arctic phytoplankton community from Disko Bay, West Greenland@en

Long-term measurements (i.e. months) of in situ pH have not previously been reported from the Arctic; this study shows fluctuations between pH 7.5 and 8.3 during the spring bloom 2012 in a coastal area of Disko Bay, West Greenland. The effect of acidification on phytoplankton from this area was studied at both the community and species level in experimental pH treatments within (pH 8.0, 7.7 and 7.4) and outside (pH 7.1) in situ pH. The growth rate of the phytoplankton community decreased during the experimental acidification from 0.50 ± 0.01/day (SD) at pH 8.0 to 0.22 ± 0.01/day at pH 7.1. Nevertheless, the response to acidification was species-specific and divided into 4 categories: I, least affected; II, affected only at pH 7.1; III, gradually affected and IV, highly affected. In addition, the colony size and chain length of selected species were affected by the acidification. Our findings show that coastal phytoplankton from Disko Bay is naturally exposed to pH fluctuations exceeding the experimental pH range used in most ocean acidification studies. We emphasize that studies on ocean acidification should include in situ pH before assumptions on the effect of acidification on marine organisms can be made.此前尚无针对北极地区的原位pH（in situ pH）时长可达数月的长期监测数据的公开报道；本研究针对西格陵兰迪斯科湾某沿岸区域的2012年春季水华期开展监测，发现该区域原位pH值在7.5至8.3区间内波动。本研究分别从群落和物种两个层面，探究了酸化胁迫对该区域浮游植物的影响：实验设置的pH处理组涵盖原位pH范围内的8.0、7.7和7.4，以及低于该范围的7.1。实验过程中，浮游植物群落的生长速率随酸化程度加剧而下降：在pH 8.0时为0.50±0.01/天（标准差SD），至pH 7.1时降至0.22±0.01/天。不过，不同物种对酸化的响应具有物种特异性，可划分为四类：I类受影响程度最低；II类仅在pH 7.1时出现响应；III类随pH降低逐渐受影响；IV类受影响程度较高。此外，部分选定物种的群体规模与链长也会受到酸化作用的影响。本研究结果显示，迪斯科湾沿岸浮游植物所处的自然pH波动范围，超出了多数海洋酸化研究采用的实验pH区间。我们强调，在针对酸化对海洋生物的影响作出假设前，海洋酸化相关研究应优先纳入原位pH监测数据。