The production and succession of harmful algae blooms (HABs) are attributed more to excessive nutrient concentrations and unbalanced nutrient stoichiometry than to other environmental drivers as the absence of long-term monitoring data. This study analyzed HABs succession patterns and key drivers in Tolo Harbour from 1986 to 2023, leveraging nearly 40 years of data. Effective governmental measures significantly improved water quality, with dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), 5-day biochemical oxygen demand (BOD5), and Escherichia coli (E. coli) concentrations decreasing by 53 %, 80 %, 45 %, and 59 %, respectively. Annual HABs events dropped from 28 to 3, and species diversity declined from 6 to 2. However, toxic species frequency rose from 21 % to 46 %. Dinoflagellates emerged as dominant initial species, with a shift in secondary dominance from diatoms to ochrophytes and toxin types from diarrhetic shellfish poisoning (DSP) to hemolytic toxins (HT). These shifts likely result from combined human and natural influences. Model simulations confirmed that red tide outbreaks, species succession, and shifts in toxin types were driven by declining pH, rising temperatures, unbalanced nitrogen-phosphorus ratios, organic nutrient increases, and algal antagonism. The study emphasizes the importance of the dual reduction of both DIN and DIP, meanwhile inorganic and organic nutrients, suggesting that overly focusing on or distract from one nutrient (e.g., DIP or DON) could lead to unintended ecological consequences, like the proliferation of rare and toxic species. We highlight the combined impacts of climate change (warming and ocean acidification) and anthropogenic activities (nutrient pollution and eutrophication) on HABs, particularly the number and toxin production. This research links policy changes to HABs dynamics, offering strategic recommendations for managing red tides and contribute novel perspectives on the impact of nutrient reduction in comparable bay ecosystems.

中文翻译：

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吐露港有害藻华对环境变化的长期演替动态和应对策略


有害藻华 （HAB） 的产生和连续更多地归因于过高的营养物质浓度和不平衡的营养物质化学计量，而不是其他环境驱动因素，因为缺乏长期监测数据。本研究利用近 40 年的数据，分析了 1986 年至 2023 年吐露港的有害藻华演替模式和主要驱动因素。有效的政府措施显著改善了水质，溶解无机氮 （DIN）、溶解无机磷 （DIP）、5 天生化需氧量 （BOD5） 和大肠杆菌 （E. coli） 浓度分别下降了 53 %、80 %、45 % 和 59 %。每年的 HABs 事件从 28 次下降到 3 次，物种多样性从 6 次下降到 2 次。然而，有毒物质的频率从 21% 上升到 46%。甲藻成为占主导地位的初始物种，次级优势从硅藻转变为赭生植物，毒素类型从腹泻性贝类中毒 （DSP） 转变为溶血毒素 （HT）。这些变化可能是人类和自然综合影响的结果。模型模拟证实，赤潮爆发、物种演替和毒素类型的变化是由 pH 值下降、温度升高、氮磷比不平衡、有机营养物质增加和藻类拮抗作用驱动的。该研究强调了 DIN 和 DIP 同时减少无机和有机营养物质的重要性，这表明过度关注或分散对一种营养物质（例如 DIP 或 DON）的注意力可能会导致意想不到的生态后果，例如稀有和有毒物种的扩散。 我们强调了气候变化（变暖和海洋酸化）和人为活动（营养物污染和富营养化）对有害藻华的综合影响，特别是数量和毒素产生。本研究将政策变化与 HAB 动态联系起来，为管理赤潮提供战略建议，并为可比海湾生态系统中营养物质减少的影响提供新的观点。