Contribution and pathways of diazotroph-derived nitrogen to zooplankton during the VAHINE mesocosm experiment in the oligotrophic New Caledonia lagoon

A groundbreaking study reveals that unicellular diazotrophic cyanobacteria (UCYN-C) significantly contribute to zooplankton nitrogen biomass through direct grazing, marking the first evidence of such a pathway. Conducted during the VAHINE mesocosm experiment in New Caledonia's oligotrophic lagoon, researchers deployed large-scale mesocosms to stimulate diazotroph production and track its impact on zooplankton. Using isotopic mixing models and 15N2 labeling, they found that UCYN-C-derived nitrogen accounted for up to 73% of zooplankton biomass in one mesocosm, while other diazotrophs like het-1 and Trichodesmium relied more on secondary pathways. The study highlights the dual role of UCYN-C in the lagoon's food web, providing critical insights into nitrogen cycling in low-nutrient tropical ecosystems.

Hunt, B. P. V., Bonnet, S., Berthelot, H., Conroy, B. J., Foster, R. A., & Pagano, M. (2016). Contribution and pathways of diazotroph-derived nitrogen to zooplankton during the VAHINE mesocosm experiment in the oligotrophic New Caledonia lagoon. Biogeosciences, 13(10), 3131–3145. https://doi.org/10.5194/bg-13-3131-2016