Loxahatchee River District, 2500 Jupiter Park Drive, Jupiter, FL 33458, United States.
Loxahatchee River District, 2500 Jupiter Park Drive, Jupiter, FL 33458, United States.
Harmful Algae. 2020 Jul;97:101851. doi: 10.1016/j.hal.2020.101851. Epub 2020 Jun 20.
In Fall 2017 a large bloom of the toxic dinoflagellate Karenia brevis developed in the Gulf of Mexico. After persisting for months, in Fall 2018 wind and water circulation patterns drove K. brevis towards the east coast of Florida. On September 29, 2018 Palm Beach County, FL beaches were closed due to respiratory and gastrointestinal issues associated with brevotoxins, and effects of brevotoxins were reported from within estuarine segments of the Loxahatchee River Estuary (LRE). This was the first apparent report of a K. brevis bloom impacting inshore portions of the LRE prompting us to question the longevity of K. brevis within a relatively shallow, well-flushed coastal-estuarine system. Within 3 days (October 1, 2018) of the first reported effects of toxins, K. brevis reached over one million cells/L and chlorophyll-a concentrations peaked at 13 µg L. Within 11 days (October 9, 2018) both K. brevis and chlorophyll pigment concentrations significantly (p-perm ≤ 0.05) dropped to an average of ≤ 30,000 cells L and < 4 µg L chlorophyll-a, indicating that the bloom had diminished. Using distance-based linear modeling (DistLM) K. brevis abundance alone explained 66% of the variation in a multivariate measure of chlorophylls (driven by carotenoids and chlorophyll-c pigment concentrations), supporting a K. brevis dominated bloom. Following the K. brevis bloom, additional HAB species K. mikimotoi and Pseudo-nitzschia spp singularly explained 6% of the variations in the multivariate measure of chlorophylls. The low explanatory power of individual HAB species, including K. brevis (≤ 0%), signifies the recovery of the phytoplankton population, where non-HAB species likely contributed to the variability in the multivariate measure of chlorophylls and overall chlorophyll-a concentrations (average of 2 µg L during non-bloom conditions). Finally, we evaluated ambient and historical water quality data to assess how these parameters changed before, during, and after the 2018 K. brevis bloom. Temperature, salinity, and nutrients in the LRE were comparable to reports of other K. brevis bloom events along the west coast of Florida. Reduced ammonia-nitrogen (NH-N) concentrations and increased tidal amplitude coincided with the end of the bloom in 2018. More work is needed to understand the specific mechanisms constraining K. brevis blooms in tidal estuaries. We suggest that future research focus on water residence times along with nutrient availability in controlling allochthonous HABs in lotic and tidally flushed estuaries. Also, we anticipate this work may stimulate additional efforts to characterize HABs using in situ observations coupled with multivariate measures of chlorophylls, though we recognize much work remains to fully define the value of this approach.
2017 年秋季，大量的有毒甲藻凯伦藻在墨西哥湾形成水华。经过数月的持续生长，2018 年秋季，风和水的环流模式将凯伦藻向东推向佛罗里达州东海岸。2018 年 9 月 29 日，由于与短裸甲藻素有关的呼吸和胃肠道问题，佛罗里达州棕榈滩县的海滩被关闭，并且在罗克斯哈奇河河口（LRE）的河口段也报告了短裸甲藻素的影响。这是首次明显报告凯伦藻水华影响 LRE 的近岸部分，促使我们质疑在相对较浅、冲刷良好的沿海河口系统中，短裸甲藻的寿命。在首次报告毒素影响后的 3 天（2018 年 10 月 1 日），短裸甲藻的数量超过一百万细胞/L，叶绿素-a 浓度达到 13 µg L。在 11 天（2018 年 10 月 9 日）内，短裸甲藻和叶绿素色素的浓度均显著（p-perm ≤ 0.05）下降到平均≤ 30,000 细胞/L 和< 4 µg L 的叶绿素-a，表明水华已经消退。使用基于距离的线性建模（DistLM），仅短裸甲藻的丰度就解释了多变量叶绿素测量值（受类胡萝卜素和叶绿素-c 色素浓度驱动）变化的 66%，支持短裸甲藻为主的水华。在短裸甲藻水华之后，其他赤潮物种凯伦藻和拟菱形藻单独解释了多变量叶绿素测量值变化的 6%。单个赤潮物种的解释能力较低，包括短裸甲藻（≤ 0%），这表明浮游植物种群正在恢复，非赤潮物种可能对多变量叶绿素测量值和整体叶绿素-a 浓度的变化（非水华条件下的平均浓度为 2 µg/L）产生影响。最后，我们评估了环境和历史水质数据，以评估在 2018 年短裸甲藻水华前后这些参数如何变化。LRE 的温度、盐度和营养物质与佛罗里达州西海岸其他短裸甲藻水华事件的报告相似。氨氮（NH-N）浓度降低和潮差增加与 2018 年水华的结束同时发生。需要做更多的工作来了解限制潮汐河口短裸甲藻水华的具体机制。我们建议，未来的研究重点应放在水停留时间以及营养物质的可利用性上，以控制流态和潮汐冲刷河口的外来赤潮。此外，我们预计这项工作可能会刺激更多使用原位观测与叶绿素多变量测量相结合的方法来描述赤潮的工作，尽管我们认识到要充分定义这种方法的价值还有很多工作要做。
