Mesozooplankton Graze on Cyanobacteria in the Amazon River Plume and Western Tropical North Atlantic.

Diazotrophic cyanobacteria, those capable of fixing di-nitrogen (N), are considered one of the major sources of new nitrogen (N) in the oligotrophic tropical ocean, but direct incorporation of diazotrophic N into food webs has not been fully examined. In the Amazon River-influenced western tropical North Atlantic (WTNA), diatom diazotroph associations (DDAs) and the filamentous colonial diazotrophs have seasonally high abundances. We sampled epipelagic mesozooplankton in the Amazon River plume and WTNA in May-June 2010 to investigate direct grazing by mesozooplankton on two DDA populations: associated with diatoms (het-1) and diatoms (het-2), and on using highly specific qPCR assays targeting nitrogenase genes ().