The Marine Science Institute, University of the Philippines, Diliman 1101, Quezon City, Philippines.
The Marine Science Institute, University of the Philippines, Diliman 1101, Quezon City, Philippines.
Harmful Algae. 2022 Jan;111:102147. doi: 10.1016/j.hal.2021.102147. Epub 2021 Dec 3.
The potential for advection to influence harmful algal bloom (HAB) spread in adjacent embayments and islands has not been investigated in the Philippines as previous studies have focused on HAB dynamics within specific embayments. Advection of HABs may be relevant in the Samar-Leyte region where adjacent sites are subject to recurrent blooms of Pyrodinium bahamense. We used different analyses to extract the potential role of advection in blooms in the region. First, we used Bayesian and information theoretic approaches applied to historical data on shellfish bans to quantify spatial dependencies in HAB occurrences between sites. Then, to determine whether such dependencies are related to circulation patterns in the region, we analyzed connectivity using a hydrodynamic model coupled with a conservative tracer-based HAB model. The Bayesian network showed that in 7 out of 11 sites, the probability of a shellfish ban depended on the state of an adjacent site. Site pairs with direct dependence relations also shared relatively high similarity in HAB occurrences over time. In the modelled network, bans tend to occur sequentially, spreading from a few sites with relatively high probabilities for ban events. A subset of sites (sources) were found to be informative of future HAB event probabilities in other sites (destinations) over time lags that are generally longer the farther the destination. Modelled surface advection showed high connectivity strengths between sources and destinations associated with circulation features, e.g., an anticyclonic current in Leyte, wind-driven coastal current in western Samar, and tidally-driven flow in the shallow embayments in southwest Samar. High connectivities were correlated with direct dependence relations in the Bayesian network. Connectivity explained up to about 1/3 of the variance in statistical dependencies between ban signals. Our results show that Paralytic Shellfish Toxin events within this region can be due to advection of blooms originating from nearby areas rather than localized cyst dynamics within an embayment. Particular sites were also identified as potential indicator sites within spatial clusters for monitoring since they are typically where blooms originate and spread from.
在菲律宾，先前的研究主要集中在特定海湾内的有害藻华 (HAB) 动态，而没有调查平流对相邻海湾和岛屿中 HAB 扩散的影响。在萨马-莱特地区，相邻地点经常发生 Pyrodinium bahamense 暴发性水华，因此平流可能会对 HAB 产生影响。我们使用不同的分析方法来提取平流在该地区水华形成中的潜在作用。首先，我们使用贝叶斯和信息理论方法，应用于贝类禁捕的历史数据，以量化站点之间 HAB 发生的空间相关性。然后，为了确定这种相关性是否与该地区的环流模式有关，我们使用耦合了保守示踪剂 HAB 模型的水动力模型来分析连通性。贝叶斯网络表明，在 11 个站点中的 7 个站点中，贝类禁捕的概率取决于相邻站点的状态。具有直接依赖关系的站点对随着时间的推移，HAB 发生的相似性也相对较高。在所建模型网络中，禁捕往往会依次发生，从少数禁捕事件概率较高的站点开始扩散。发现一组站点（源）随着时间的推移，对其他站点（目标）的未来 HAB 事件概率具有信息性，而时间滞后通常随着目标站点的距离增加而变长。模型表面平流显示了源和目标之间的高连通强度，这与环流特征有关，例如莱特岛的反气旋环流、西部萨马的风驱动沿海流以及西南萨马浅海湾的潮汐流。高连通性与贝叶斯网络中的直接依赖关系相关。连通性解释了禁捕信号之间统计相关性的约 1/3 变化。我们的结果表明，该地区的麻痹性贝类毒素事件可能是由于来自附近地区的水华平流引起的，而不是海湾内局部胞囊的动态。由于它们通常是水华起源和传播的地方，因此还确定了特定站点作为监测的潜在指示站点，将其纳入空间聚类中。
