CSS Inc. under contract to NOAA National Centers for Coastal Ocean Science, 1315 East West Highway, Silver Spring, MD 20910.
NOAA National Centers for Coastal Ocean Science, 1315 East West Highway, Silver Spring, MD 20910.
Harmful Algae. 2020 Nov;99:101927. doi: 10.1016/j.hal.2020.101927. Epub 2020 Oct 26.
In July 2009, an unusually intense bloom of the toxic dinoflagellate Alexandrium catenella occurred in the Gulf of Maine. The bloom reached high concentrations (from hundreds of thousands to one million cells L) that discolored the water and exceeded normal bloom concentrations by a factor of 1000. Using Medium Resolution Imaging Spectrometer (MERIS) imagery processed to target chlorophyll concentrations (>2 µg L), patches of intense A. catenella concentration were identified that were consistent with the highly localized cell concentrations observed from ship surveys. The bloom patches were generally aligned with the edge of coastal waters with high-absorption. Dense bloom patches moved onshore in response to a downwelling event, persisted for approximately one week, then dispersed rapidly over a few days and did not reappear. Coupled physical-biological model simulations showed that wind forcing was an important factor in transporting cells onshore. Upward swimming behavior facilitated the horizontal cell aggregation, increasing the simulated maximum depth-integrated cell concentration by up to a factor of 40. Vertical convergence of cells, due to active swimming of A. catenella from the subsurface to the top layer, could explain the additional 25-fold intensification (25 × 40=1000-fold) needed to reach the bloom concentrations that discolored the water. A model simulation that considered upward swimming overestimated cell concentrations downstream of the intense aggregation. This discrepancy between model and observed concentrations suggested a loss of cells from the water column at a time that corresponded to the start of encystment. These results indicated that the joint effect of upward swimming, horizontal convergence, and wind-driven flow contributed to the red water event, which might have promoted the sexual reproduction event that preceded the encystment process.
2009 年 7 月，缅因湾海域出现了一场异常强烈的有毒甲藻亚历山大藻密集生长现象。此次密集生长达到了高浓度（从几十万到一百万细胞每升），使水变色，并比正常密集生长高出 1000 倍。使用中分辨率成像光谱仪（MERIS）对叶绿素浓度（>2μg/L）进行处理，识别出密集的 A. catenella 浓度斑块，与从船只调查中观察到的高度局部细胞浓度一致。密集生长的斑块通常与沿海高吸收水域的边缘对齐。密集的水华斑块因下沉事件而向海岸移动，持续了大约一周，然后在几天内迅速扩散，并且不再出现。耦合物理-生物模型模拟表明，风的作用力是将细胞输送到岸上的一个重要因素。向上游动的行为促进了细胞的水平聚集，使模拟的最大深度积分细胞浓度增加了 40 倍。由于 A. catenella 从次表层到顶层的主动游动，导致细胞垂直汇聚，这可以解释额外的 25 倍的密集化（25×40=1000 倍），从而达到使水变色的密集生长浓度。考虑到向上游动的模型模拟高估了密集聚集下游的细胞浓度。模型和观察到的浓度之间的这种差异表明，在对应的包囊过程开始时，细胞从水柱中流失。这些结果表明，向上游动、水平汇聚和风驱动流的共同作用促成了红色水事件，这可能促进了包囊过程之前的有性生殖事件。
