Department of Marine Biology, Texas A&M University at Galveston, Galveston, Texas, United States.
Department of Marine Biology, Texas A&M University at Galveston, Galveston, Texas, United States.
Aquat Toxicol. 2019 Jan;206:43-53. doi: 10.1016/j.aquatox.2018.11.004. Epub 2018 Nov 6.
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/F) or electron transfer rates (ETR) compared to Control communities. In contrast, both F/F and ETR 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 年的墨西哥湾深海地平线石油泄漏事件中，化学分散剂科里克斯被广泛应用于墨西哥湾的大片区域。海洋浮游植物通过产生细胞外聚合物物质 (EPS) 在聚集体形成中发挥关键作用，这是生物碳泵的重要步骤。本研究通过 72 小时中观实验，研究了石油和分散剂对墨西哥湾自然海洋浮游植物群落组成和生理的影响，以及对碳输出的影响。这些群落使用油的水容纳分数 (WAF) 进行处理，通过将马孔多替代油添加到天然海水中并在黑暗中混合 24 小时来制备。以类似的方式制备化学增强 WAF (CEWAF)，但使用油和分散剂科里克斯的混合物以 20:1 的比例以及稀释的 CEWAF (DCEWAF)。与对照群落相比，暴露于 WAF 的浮游植物群落的 PSII 量子产量 (F/F) 或电子传递速率 (ETR) 没有明显变化。相比之下，CEWAF 或 DCEWAF 处理的群落中，F/F 和 ETR 都迅速下降。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) 天线大小和 PSII 连接因子，这表明 PSII 下游的过程受到了影响。在 72 小时暴露结束时，使用 18S rRNA 测序对每个实验罐中的真核生物群落组成进行了特征描述。在对照和 WAF 处理中，硅藻占主导地位（分别为 52%和 56%的相对丰度），而在 CEWAF 和 DCEWAF 处理中，异养眼虫占主导地位（分别为 51%和 84%）。在所有处理中，硅藻对自养真核生物群落的相对贡献最大。CEWAF 罐中的 EPS 浓度是其他处理的四倍。随着时间的推移，颗粒大小分布（聚集体的代理）的变化表明，CEWAF 和 DCEWAF 处理比 WAF 或对照处理更容易发生颗粒聚集。我们的研究结果表明，与单独的石油相比，化学分散的石油对浮游植物的生理、群落结构和聚集动态具有更负面的影响，这可能对影响碳和石油在水柱中分布和周转的输出过程产生影响。
