This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Who isn't familiar with the colorful coral reefs from movies like "Finding Nemo" or "The Little Mermaid"? Unfortunately, the reality is often quite different, as these vital ecosystems are under pressure worldwide.
Climate change and pollution are causing corals to bleach and die. Even the most resilient coral reefs of the United States are now threatened. The reefs in the Flower Garden Banks National Marine Sanctuary in the northern Gulf of Mexico were long considered exceptionally healthy due to their high coral coverage.
But rising water temperatures and an excess of nutrients are causing even these reefs to lose their resilience. An international research team led by the Max Planck Institute for Chemistry and Louisiana State University has discovered that the high levels of nitrogen in the northern Gulf originate from the Mississippi River and are attributable to fertilizer use. The team analyzed nitrogen isotopes in the calcareous skeletons of corals and used the data to reconstruct the source of nitrogen in seawater over the past 270 years.
The results show that, in recent decades, more than 60% and, during certain periods, up to 80% of the nitrogen in the Flower Garden Banks originated from the Mississippi River basin. According to the study, published in the journal Science Advances, the highest nitrogen inputs occurred in 2016 and between 2022 and 2023. It was precisely during these years that the reefs suffered exceptional heat waves, massive coral bleaching events and increased disease outbreaks.
The Mainz researchers analyzed core samples from star corals in the northern Gulf of Mexico. These stony corals grow slowly but continuously and live to a very old age. Similar to the annual rings of trees, the corals form their calcareous skeletons in layers, making them an excellent archive of environmental conditions.
As a result, the scientists were able to determine the nitrogen isotopes present in the corals from 1753 to 2023. The isotopic fingerprint of nitrogen (N), more specifically, the ratio of heavy 15N to light 14N, carries information about the origin of the nutrients consumed by the coral. Using this technique, the team could determine the origin of the water in which the corals grew.
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