International Journal of Marine Science, 2025, Vol.15, No.6, 292-302 http://www.aquapublisher.com/index.php/ijms 300 8.3 Eutrophication and harmful algal blooms caused by excessive phosphorus input Under the influence of human activities, many nearshore and semi-enclosed water bodies have experienced frequent eutrophication and harmful algal blooms due to excessive phosphorus input. Phosphorus is often one of the key drivers contributing to the overgrowth of algae: When estuaries and bays receive high concentrations of phosphorus from agricultural fertilizers and urban sewage, algae can take up nitrogen together and multiply rapidly, forming algal blooms or "red tides" (Gao et al., 2025). Some cyanobacteria can stand out under phosphorus-rich and low N:P conditions, and their nitrogen fixation function enables them to multiply on a large scale without being restricted by nitrogen supply. Such algal blooms not only deteriorate water quality and reduce transparency, but also consume oxygen in the water, causing hypoxia at the bottom and the death of organisms. More seriously, the hypoxic environment caused by eutrophication will prompt the sediment to release more phosphorus (increased internal load), which further promotes the next round of algal bloom, forming a vicious cycle (Xiao et al., 2019). Once this happens, it is very difficult for the water body to restore itself to a low nutritional level. Therefore, to prevent and control Marine eutrophication, it is essential to focus on reducing phosphorus emissions at the source and supplement it with ecological restoration and other measures to break the positive feedback of the phosphorus cycle, reduce the risk of red tides, and maintain the health of coastal ecosystems. Acknowledgments Thank you to Dr. Kora Li for his technical support in data analysis and visualization, and also thank the members of the research team for their discussions and suggestions during the paper writing. Conflict of Interest Disclosure The authors affirm that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest. References Boxhammer T., Taucher J., Bach L., Achterberg E., Algueró-Muñíz M., Bellworthy J., Czerny J., Esposito M., Haunost M., Hellemann D., Ludwig A., Yong J., Zark M., Riebesell U., and Anderson L., 2018, Enhanced transfer of organic matter to higher trophic levels caused by ocean acidification and its implications for export production: A mass balance approach, PLoS ONE, 13(5): e0197502. https://doi.org/10.1371/journal.pone.0197502 Brady M., Tostevin R., and Tosca N., 2022, Marine phosphate availability and the chemical origins of life on Earth, Nature Communications, 13: 5162. https://doi.org/10.1038/s41467-022-32815-x Browning T., and Moore M., 2023, Global analysis of ocean phytoplankton nutrient limitation reveals high prevalence of co-limitation, Nature Communications, 14: 5014. https://doi.org/10.1038/s41467-023-40774-0 Browning T., Achterberg E., Yong J., Rapp I., Utermann C., Engel A., and Moore M., 2017, Iron limitation of microbial phosphorus acquisition in the tropical North Atlantic, Nature Communications, 8: 15465. https://doi.org/10.1038/ncomms15465 Carrillo P., Medina-Sánchez J., Herrera G., Durán C., Segovia M., Cortés D., Salles S., Korbee N., Figueroa F., and Mercado J., 2015, Interactive effect of UVR and phosphorus on the coastal phytoplankton community of the Western Mediterranean Sea: unravelling eco-physiological mechanisms, PLoS ONE, 10(12): e0142987. https://doi.org/10.1371/journal.pone.0142987 Dam T., Angert A., Krom M., Bigio L., Hu Y., Beyer K., Mayol-Bracero O., Santos-Figueroa G., Pio C., and Zhu M., 2021, X-ray spectroscopic quantification of phosphorus transformation in saharan dust during trans-atlantic dust transport, Environmental Science and Technology, 55(18): 12694-12703. https://doi.org/10.1021/acs.est.1c01573 Duan Z., Liang J., Shi L., Xu Y., Gao W., and Tan X., 2025, Eutrophication heterogeneously enhances organic matter and phosphorus exchanges among dissolved particulate and sedimentary phases in a large shallow lake, Environmental Science and Technology, 59(26): 13264-13274. https://doi.org/10.1021/acs.est.4c12091 Duhamel S., 2024, The microbial phosphorus cycle in aquatic ecosystems, Nature Reviews, Microbiology, 23(4): 239-255. https://doi.org/10.1038/s41579-024-01119-w Fru E.C., Bahri J., Brosson C., Bankole O., Aubineau J., Albani A., Nederbragt A., Oldroyd A., Skelton A., Lowhagen L., Webster D., Fantong W., Mills B., Alcott L., Konhauser K., and Lyons T., 2023, Transient fertilization of a post-Sturtian Snowball ocean margin with dissolved phosphate by clay minerals, Nature Communications, 14: 8418. https://doi.org/10.1038/s41467-023-44240-9
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