ABSTRACTWe examined the physiology and biochemistry associated with the iron‐limited continuous culture of the halotolerant cyanobacteriumSynechococcusPCC 7002. Biomass production, photosynthetic pigment levels, photosynthetic efficiency, and the production of hydroxamate‐ and catechol‐type siderophores are reported for cells grown over a range of available iron concentrations. The relationship between the yield ofSynechococcusPCC 7002 in iron‐limited chemostats and the concentration of available iron was not linear. SynechococcusPCC 7002 expressed an inducible physiological response that led to alterations either in the cellular iron quotient or, more likely, in levels of available iron due to induced iron‐scavenging processes. During iron limitation these cyanobacteria produced components consistent with the activation of a high‐affinity iron transport system; both hydroxamate‐ and catechol‐type siderophores were detected. Iron‐limitedSynechococcusPCC 7002 also reduced CO2fixation rates from luxury levels to a rate that matched the cellular growth rate, presenting interesting implications for oceanic c