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

\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.