2000-2024년 여수 해역의 Margalefidinium polykrikoides에 의한 유해성 적조 발생 특성: 영양염류 농도 및 비율을 중심으로

초록

Phytoplankton contribute more than 50% of marine primary production and form the foundation of global carbon cycling and marine food webs. However, when certain harmful species proliferate mas-sively under changing environmental conditions, red tides occur, causing serious problems such as disrup-tion of marine ecosystems, damage to fisheries, and risks to human health. Therefore, identifying the en-vironmental conditions under which harmful algal species form large-scale blooms, and predicting their occurrence, is crucial to minimizing the impacts on fisheries-dependent communities in Korea. This study analyzed the bloom mechanisms of major harmful algal species in the southern coastal waters of Korea using 25 years (2000–2024) of long-term data accumulated from the Marine Environment Monitoring Network and the harmful algal bloom (HAB) alert system of the National Institute of Fisheries Science, Korea. The results showed that Margalefidinium polykrikoides (= Cochlodinium polykrikoides) was the most frequent bloom-forming species, with 435 recorded events over the past 25 years, and that its blooms occurred most frequently in August in the Yeosu region. Nutrient conditions during the peak bloom years of 2001, 2015, and 2013 revealed extremely low N:P ratios, with surface values below 4.8 and bottom values below 3.8, indicating that large-scale M. polykrikoides blooms were associated with low N:P environments. In addition, we newly confirmed that the closer the nitrate concentration differ-ence between surface and bottom waters approached zero, the more frequently blooms occurred. Fur-thermore, the results demonstrated that large-scale blooms of M. polykrikoides were concentrated under nitrogen-depleted and silicate-rich conditions, suggesting that the combined variation in nutrient concen-trations and stoichiometric ratios (N:P:Si) acts as a key regulatory driver of bloom development. It was also revealed that large-scale red tides caused by M. polykrikoides occur more frequently as the differ-ence in dissolved inorganic phosphate concentration between the bottom and surface layers increases. This implies that if bottom-water phosphate concentrations continue to rise and the imbalance of nitrate and silicate between surface and bottom waters intensifies, the frequency and magnitude of M. polykri-koides blooms in the Yeosu coastal region are likely to increase. These results indicate a potential causal link between changes in nutrient structure and bloom formation, highlighting the importance of continu-ous and integrated monitoring of nutrient concentrations and ratios to better predict bloom dynamics. These findings provide novel evidence of the key environmental conditions driving M. polykrikoides blooms, and are expected to enhance the accuracy of future bloom prediction models while establishing an essential academic and societal basis for effective management strategies.

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