Our research is the first approximation to understand the δ¹³C macroalgal variability in one of the most diverse marine ecosystems in the world, the Gulf of California. The life-form is the principal cause of δ¹³C macroalgal variability, mainly taxonomy. However, changes in habitat characteristics and environmental conditions also influence the δ¹³C macroalgal variability. The δ¹³C macroalgae is indicative of carbon concentration mechanisms and isotope discrimination during carbon assimilation.