サルガッサム藻類の大発生の駆動因を特定（The Driver of Sargassum Blooms）

2025-11-05 マックス・プランク研究所

マックス・プランク化学研究所の研究で、大西洋のサルガッサム（ホンダワラ属）大量発生の要因が明らかになった。コーラル掘削コアの分析により、リンを多く含む深層水が風による湧昇で表層に押し上げられ、窒素固定性シアノバクテリアを活性化させることが判明。これらはサルガッサムと共生し、窒素供給を通じて急速な藻類増殖を促進する。栄養塩源は陸由来ではなく深海起源であることが確認され、2011年以降拡大する「大西洋サルガッサム帯」の形成メカニズムを説明した。この知見は、カリブ海やメキシコ湾沿岸での藻類漂着の予測改善や沿岸生態系保全に貢献する。

＜関連情報＞

赤道リンの湧昇が大西洋の窒素固定とホンダワラ類の繁殖を促進 Equatorial upwelling of phosphorus drives Atlantic N2 fixation and Sargassum blooms

Jonathan Jung,Nicolas N. Duprey,Alan D. Foreman,Juan Pablo D’Olivo,Carolin Pellio,Yeongjun Ryu,Erin L. Murphy,Baseerat Romshoo,Diego K. Kersting,Gabriel O. Cardoso,Tanja Wald,François Fripiat,Carlos Jimenez,Eberhard Gischler,Paolo Montagna,Carlos Alonso-Hernández,Miguel Gomez-Batista,Christina Treinen-Crespo,José Carriquiry,Maria Rosabelle Ong,Nathalie F. Goodkin,Reia Guppy,Hedy Aardema,Hans Slagter,… Alfredo Martínez-García
Nature Geoscience Published:05 November 2025
DOI:https://doi.org/10.1038/s41561-025-01812-2

Abstract

The Great Atlantic Sargassum Belt first appeared in 2011 and quickly became the largest interconnected floating biome on Earth. In recent years, Sargassum stranding events have caused substantial ecological and socio-economic impacts in coastal communities. Sargassum requires both phosphorus (P) and nitrogen (N) for growth, yet the primary sources of these nutrients fuelling the extensive Sargassum blooms remain unclear. Here we use coral-bound N isotopes to reconstruct N₂ fixation, the ultimate source of the ocean’s bioavailable N, across the Caribbean over the past 120 years. Our data indicate that changes in N₂ fixation were primarily controlled by multidecadal and interannual changes in equatorial Atlantic upwelling of ‘excess P’, that is, P in stoichiometric excess relative to fixed N. We show that the supply of excess P from equatorial upwelling and N from the N₂ fixation response can account for the majority of Sargassum variability since 2011. Sargassum dynamics are best explained by their symbiosis with N₂-fixing epiphytes, which render the macroalgae highly competitive during strong equatorial upwelling of excess P. Thus, the future of Sargassum in the tropical Atlantic will depend on how global warming affects equatorial Atlantic upwelling and the climatic modes that control it.