An examination of niche separation in two primary Trichodesmium clades along the West Florida Shelf

Kristina Confesor1, Corday Selden2, Kimberly Powell3, Angela N Knapp4, Kristen N Buck5, Phoebe Dreux Chappell2 and Laura Donahue6, (1)Heidelberg University, Tiffin, OH, United States, (2)Old Dominion University, Ocean, Earth and Atmospheric Sciences, Norfolk, United States, (3)Old Dominion University, Ocean, Earth, and Atmospheric Sciences, Norfolk, VA, United States, (4)Florida State University, Earth, Ocean, and Atmospheric Sciences, Tallahassee, FL, United States, (5)Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States, (6)Haverford College, Haverford, United States
\textit{Trichodesmium} is a genus of dinitrogen-fixing cyanobacteria that is commonly observed along the West Florida Shelf. This project aimed to quantify the gene abundance (gene copies/L) of the two primary \textit{Trichodesmium} clades (\textit{Trichodesmium erythraeum} and \textit{Trichodesmium thiebautii}), identify any correlations with the hydrographic data, and distinguish any trends in niche distribution in samples collected on the West Florida Shelf from three separate cruises. In general, \textit{T. thiebautii} was more abundant further offshore, while \textit{T. erythraeum} was abundant closer to shore. There was a negative correlation (Spearman r = -0.51, p< 0.01) between salinity and \textit{T. erythraeum} in April 2019. In addition, a weak but statistically significant negative correlation (r=-0.26, p < 0.05) was found between salinity and \textit{T. erythraeum} abundance across all the sampling years (2015, 2018, and 2019). There was not a statistically significant positive correlation between \textit{T. thiebautii} and salinity in just the 2019 samples. However, a statistically significant positive correlation was found for salinity and \textit{T. Thiebautii} gene abundance when all 3 sampling years were examined (r = 0.44, p < 0.001). While a lack of nearshore sampling in 2015 made it difficult to conclusively identify specific trends in niche distribution, 2018 and 2019 samples show a consistent coastal vs. open ocean niche separation for the two clades.