An analysis of the variability in <i>?</i><sup>13</sup>C in macroalgae from the Gulf of California: indicative of carbon concentration mechanisms and isotope discrimination during carbon assimilation

Abstract. The isotopic composition of carbon in macroalgae (?13C) is highly variable, and its prediction complex concerning terrestrial plants. determinants ?13C macroalgal variations were analyzed a large stock specimens that vary taxa morphology collected shallow marine habitats the Gulf California (GC) with distinctive environmental conditions. A variability (?34.6 ‰ to ?2.2 ‰) was observed. Life-forms (taxonomy 57 %, structural organization 34 %) explain related use physiology. Environmental conditions influenced values but did not change physiology, which most likely inherently species-specific. Values used as indicators presence or absence concentrating mechanisms (CCMs) integrative isotope discrimination during assimilation life cycle macroalgae. Based on signals, classified three strategies relative capacity CCM: (1) HCO3- uptake (?13C > ?10 ‰), (2) using mix CO2 (-10<?13C ?30 (3) diffusive entry < ‰). Most species showed indicates CCM uptake. also widespread among GC macroalgae, many Ochrophyta species. Few belonging Rhodophyta relied exclusively, while calcifying included only Amphiroa Jania. signature evidenced activity CCM, it inconclusive about preferential photosynthesis type expressed In study strategies, diverse, species-specific, complementary techniques tools are required.