Cyanobacteria are significant and at times dominant contributors to estuarine, coastal and open ocean primary production and fixed nitrogen inputs. CO₂ and N₂ fixation can be controlled by single or combined nutrient supplies, depending on the influence of external vs. internal inputs. Nitrogen limitation characterizes much of the world's oceanic surface waters, providing a vast niche for cyanobacteria capable of N₂ fixation. The filamentous planktonic N₂ fixers, Trichodesmium and Richelia (endosymbiont in the diatom Rhizosolenia) can form large (< 100's of km²) surface blooms in nutrient-deplete, oligotrophic open ocean waters. Here, the availability of iron (Fe), a cofactor in the N₂ fixing enzyme complex nitrogenase, may control N₂ fixation, as shown subtropical W. Atlantic and Caribbean waters. The picoplanktonic (< 5 μm) genera Synechococcus, Synechocystis, and Prochlorococcus are important (i.e., 20 to > 50%) contributors to phytoplankton productivity and biomass. These non N₂ fixers rely on small size (i.e., high surface to volume ratio) and efficient light harvesting abilities, to optimize growth in poorly-illuminated, nutrient-rich deep waters. Marine cyanobacteria exhibit various morphological, physiological, and ecological strategies aimed at co-optimizing diazotrophy, photosynthesis and nutrient (N, P, Fe) sequestration. These include; buoyancy regulation to facilitate access to near-surface sunlight (energy) and nutrient-rich deeper water, aggregation as colonies supporting nutrient-exchanging consortial interactions with microheterotrophs and invertebrate grazers, endosymbioses, intracellular nitrogen and phosphorus storage, heterotrophic and photoheterotrophic capabilities. Certain cyanobacterial genera can exploit nutrient-enriched estuaries and seas (e.g. Baltic), sometimes as persistent nuisance (i.e. hypoxia/anoxia-generating, toxic) blooms. If N₂ fixing cyanobacteria predominate as planktonic blooms (Nodularia, Aphanizomenon) or benthic mats (Lyngbya, Oscillatoria), or if high rates of external N loading occur, N+P co-limitation or exclusive P limitation may dominate. In non-N₂ fixing communities, Fe may synergistically interact with combined N, especially NO₃^-, to enhance growth. Increasing anthropogenic N and Fe enrichment (runoff, atmospheric deposition, groundwater) supports large-scale eutrophication which, in addition to degrading water quality, affects air-water CO₂ fluxes, oceanic C, N and other nutrient budgets.

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   |wiki=    Wicri/Asie
   |area=    AustralieFrV1
   |flux=    Main
   |étape=   Exploration
   |type=    RBID
   |clé=     Pascal:00-0054123
   |texte=   Physical-chemical constraints on cyanobacterial growth in the Oceans
}}