An analysis of the variability in δ13C 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 (δ13C) is highly variable, and its prediction is complex concerning terrestrial plants. The determinants of δ13C macroalgal variations were analyzed in a large stock of specimens that vary in taxa and morphology and were collected in shallow marine habitats in the Gulf of California (GC) with distinctive environmental conditions. A large δ13C variability (-34.6ĝ€¯‰ to -2.2ĝ€¯‰) was observed. Life-forms (taxonomy 57ĝ€¯%, morphology and structural organization 34ĝ€¯%) explain the variability related to carbon use physiology. Environmental conditions influenced the δ13C macroalgal values but did not change the physiology, which is most likely inherently species-specific. Values of δ13C were used as indicators of the presence or absence of carbon concentrating mechanisms (CCMs) and as integrative values of the isotope discrimination during carbon assimilation in the life cycle macroalgae. Based on δ13C signals, macroalgae were classified in three strategies relative to the capacity of CCM: (1) HCO3- uptake (δ13Cĝ€¯>ĝ€¯-10ĝ€¯‰), (2) using a mix of CO2 and HCO3- uptake (-10 ĝ€¯-30ĝ€¯‰), and (3) CO2 diffusive entry (δ13Cĝ€¯