AME prepress abstract  -  doi: 10.3354/ame01810

Distribution of the marine cyanobacteria Trichodesmium and its association with iron-rich particles in the SW Atlantic Ocean

Mariana Bernardi Bif*, João Sarkis Yunes

*Email: marianabif@gmail.com

ABSTRACT: The genus Trichodesmium is commonly found in nutrient-limited tropical and subtropical ocean basins due to their capacity to fix atmospheric nitrogen (N2). However, N2 fixation requires supplementary iron and phosphorus and can potentially become limiting nutrients for Trichodesmium’s growth. In order to understand their ecology and distribution in a poorly studied region of the South Atlantic Ocean, we collected physical, chemical and biological data from dense populations. Despite relatively low concentrations of phosphate (<0.35 µM), we found Trichodesmium throughout the region, with the northernmost stations having the highest abundances in the surface layer (>157000 trichomes l–1). Using light microscopy, a mixture of biogenic and lithogenic particles were found attached to the colonies. Their composition was analyzed and revealed high concentrations of iron (12–29% of the average particle composition), phosphorus (1–3%) and zinc (1–5%). Particles from the southernmost stations were unique in their titanium composition (6% at Stn 09 and 5% at Stn 16), which was considered a tracer for the regional input of sediments by the La Plata River plume. Bacteria was associated with some Trichodesmium colonies, suggesting particle dissolution and remineralization as a mechanism for increasing the availability of nutrients, thus facilitating N2 fixation. This study provides new information about the distribution of Trichodesmium in the South Atlantic Ocean and its association with particles and bacteria as an adaptation for extra nutrient acquisition.