A historical analysis of the potential nutrient supply from the N2 fixing marine cyanobacterium Trichodesmium spp. to Karenia brevis blooms in the eastern Gulf of Mexico

Abstract

Blooms of Karenia brevis co-occur with populations of the N2 fixing cyanobacterium Trichodesmium on the West Florida shelf where iron (Fe) and phosphorus (P) supplies have been shown to control the growth potential of these cyanophytes. Historical data records of Trichodesmium presence and abundance (1960–2008) were analyzed in relation to the nutrient requirements of annually coincident K. brevis blooms, focusing on the potential direct supply of nitrogen (N) via N2-fixation with subsequent excretion of recently fixed N2 as NH4+ and dissolved organic nitrogen and indirect transfer from Trichodesmium biomass (as particulate N and P) during cell death. While release of “new” N from biological N2-fixation can supply up to 40% of the 2001 large red tide (9.5 × 106 cells L−1), estimates of the total N available, including the regeneration of additional nutrients supplied from particulate stocks aggregated within surface populations of observed Trichodesmium biomass during cell death, suggest that up to 100% of N and P requirements of such large blooms can be met from N2-fixation sources.