Researchers at the University of North Carolina at Chapel Hill conducted an intriguing study focusing on nitrogen fixation among diazotrophs living alongside sargassum, a brown macroalgae that floats on the ocean’s surface. These microorganisms can convert nitrogen into a usable form for other marine life.
The study, published in PLOS ONE, sheds light on the significance of nitrogen fixation in sargassum communities, which has been overlooked in previous research. This oversight could have led to an underestimation of the Atlantic nitrogen budget’s overall nitrogen fixation.
Lindsay Dubbs, a research associate professor at the UNC Institute for the Environment and the Coastal Studies Institute at East Carolina University, expressed excitement about the findings. The study demonstrated sargassum’s vital role in supporting marine productivity, countering the negative focus on sargassum overgrowth in Florida and the Caribbean.
Claire Johnson, a Ph.D. student at UNC College of Arts and Sciences and a graduate research assistant at the Coastal Studies Institute, emphasized the novelty of the dataset they contributed. The long-term analysis provided an updated view of nitrogen fixation, drawing attention to an area that has been neglected for decades.
Comparing the nitrogen fixation rate with other marine sources, the team found that sargassum communities outpaced commonly studied nitrogen-fixing organisms, such as planktonic diazotrophs and coastal epiphytes. This discovery highlights the significant contribution of sargassum to the marine nitrogen cycle and its potential role in sargassum blooms.
Collecting data on this process posed challenges, but the team’s proximity to the Gulf Stream facilitated day-long trips to collect samples seasonally and process them promptly. They carefully managed whole fronds of the seaweed in large tubs at the laboratory to preserve the microorganisms for analysis. The team collected samples over a six-year period to establish a robust dataset.
Sargassum thrives in various regions, including the Caribbean Sea, Gulf of Mexico, Gulf Stream, and Sargasso Sea. The study’s comprehensive view of nitrogen fixation rates in North Carolina opens avenues for further research on how these rates vary across a wider geographic range.
Considering the current sargassum blooms in the South Atlantic, the research gains even greater significance. Johnson emphasized that if epiphytes on sargassum in this population fix nitrogen on a similar scale to what they observed, it could substantially impact the Atlantic marine nitrogen budget.
Dubbs remains optimistic that their long-term dataset will continue to unveil new insights about sargassum’s importance and complexity. The research opens doors to better understand the intricate interactions between sargassum and the marine ecosystem, and it may provide valuable insights to address challenges related to sargassum blooms in different regions.