What is an organism to do when it has two tasks to perform but only enough resources to do one? Crocosphaera watsonii solves the problem by doing only one of the tasks at a time and recycling the reources. The proteins that C. watsonii uses to perform photosynthesis and the ones it uses to fix nitrogen gas both require iron; however, iron is a scarce mineral in the open ocean. By using its iron reserves in photosynthetic proteins during the day, then breaking the proteins down and reusing the iron for the nitrogen fixing proteins at night, C. watsonii is able to survive and flourish without much iron, though it does require an input of energy to keep the recyling process going.
"This iron conservation strategy is analogous to the maritime practice of hotbunking, referring to ships that sail with more sailors (metalloenzyme requirements) than bunks (iron atoms), where sailors on opposing shifts share the same bunk—keeping the bunks continually hot (or iron atoms in use)...Iron conservation strategies in Crocosphaera provided an ecological advantage in the low iron environments of the open ocean." (Saito et al. 2011:2187)
"Sharing cellular iron between photosynthesis and nitrogen fixation machinery allowed the model hotbunking diazotrophs to not only expand their habitat, but also to have higher biomass per mole of available iron." (Saito et al. 2011:2188)