During the 2010 Deepwater Horizon oil spill, the chemical dispersant Corexit was applied over vast areas of the Gulf of Mexico. Marine phytoplankton play a key role in aggregate formation through the production of extracellular polymeric materials (EPS), an important step in the biological carbon pump. This study examined the impacts of oil and dispersants on the composition and physiology of natural marine phytoplankton communities from the Gulf of Mexico during a 72-hour mesocosm experiment and consequences to carbon export. The communities were treated using the water accommodated fraction (WAF) of oil, which was produced by adding Macondo surrogate oil to natural seawater and mixed for 24 h in the dark. A chemically enhanced WAF (CEWAF) was made in a similar manner, but using a mixture of oil and the dispersant Corexit in a 20:1 ratio as well as a diluted CEWAF (DCEWAF). Phytoplankton communities exposed to WAF showed no significant changes in PSII quantum yield (F_v/F_m) or electron transfer rates (ETR_max) compared to Control communities. In contrast, both F_v/F_m and ETR_max declined rapidly in communities treated with either CEWAF or DCEWAF. Analysis of other photophysiological parameters showed that photosystem II (PSII) antenna size and PSII connectivity factor were not altered by exposure to DCEWAF, suggesting that processes downstream of PSII were affected. The eukaryote community composition in each experimental tank was characterized at the end of the 72 h exposure time using 18S rRNA sequencing. Diatoms dominated the communities in both the control and WAF treatments (52 and 56% relative abundance respectively), while in CEWAF and DCEWAF treatments were dominated by heterotrophic Euglenozoa (51 and 84% respectively). Diatoms made up the largest relative contribution to the autotrophic eukaryote community in all treatments. EPS concentration was four times higher in CEWAF tanks compared to other treatments. Changes in particle size distributions (a proxy for aggregates) over time indicated that a higher degree of particle aggregation occurred in both the CEWAF and DCEWAF treatments than the WAF or Controls. Our results demonstrate that chemically dispersed oil has more negative impacts on photophysiology, phytoplankton community structure and aggregation dynamics than oil alone, with potential implications for export processes that affect the distribution and turnover of carbon and oil in the water column.

在2010年Deepwater Horizo​​n漏油事件中，化学分散剂Corexit被应用到墨西哥湾的广大地区。海洋浮游植物通过产生细胞外聚合物（EPS）而在聚集体形成中起关键作用，这是生物碳泵中的重要步骤。这项研究在72小时的中观试验中考察了油和分散剂对来自墨西哥湾的天然海洋浮游植物群落组成和生理的影响以及对碳出口的影响。使用油的水份（WAF）对这些社区进行处理，该油是通过将Macondo替代油添加到天然海水中并在黑暗中混合24小时而产生的。以类似的方式制备化学增强的WAF（CEWAF），但使用油和分散剂Corexit的混合物以20：1个比率以及稀释的CEWAF（DCEWAF）。暴露于WAF的浮游植物群落未显示PSII量子产率的显着变化（F_v / F _m）或电子传输速率（ETR _max）与对照组相比。相反，F _v / F _m和ETR _maxCEWAF或DCEWAF处理的社区中的艾滋病感染率迅速下降。对其他光生理参数的分析表明，暴露于DCEWAF不会改变光系统II（PSII）的天线尺寸和PSII连接因子，这表明PSII下游的过程受到了影响。使用18S rRNA测序在暴露时间72 h结束时，对每个实验槽中的真核生物群落组成进行了表征。在对照和WAF处理中，硅藻均占主导地位（相对丰度分别为52％和56％），而在CEWAF和DCEWAF处理中，以异养藻类（Euglenozoa）为主（分别为51％和84％）。在所有治疗中，硅藻对自养真核生物群落的贡献最大。与其他处理相比，CEWAF储罐中的EPS浓度高出四倍。粒度分布（代表聚集体）随时间的变化表明，CEWAF和DCEWAF处理中发生的颗粒聚集程度均高于WAF或对照。我们的结果表明，化学分散的油对光生理，浮游植物群落结构和聚集动力学的影响要比仅对油的影响更大，对出口过程的潜在影响可能会影响水柱中碳和油的分布和周转。