High prevalence of diffusive uptake of CO 2 by macroalgae in a temperate subtidal ecosystem

• Published in: Photosynthesis Research
• Main Authors: Cornwall, CE, Revill, AT, Hurd, CL
• Format: Article in Journal/Newspaper
• Language: English
• Published: Kluwer Academic Publ 2015
• Subjects: Environmental Sciences; Ecological Applications; Ecological Impacts of Climate Change; Ocean acidification
• Online Access: https://doi.org/10.1007/s11120-015-0114-0; http://www.ncbi.nlm.nih.gov/pubmed/25739900; http://ecite.utas.edu.au/104209

Productivity of most macroalgae is not currently considered limited by dissolved inorganic carbon (DIC), as the majority of species have CO 2 -concentrating mechanisms (CCM) allowing the active uptake of DIC. The alternative, diffusive uptake of CO 2 (non-CCM), is considered rare (09% of all macroalgal cover in a given ecosystem), and identifying species without CCMs is important in understanding factors controlling inorganic carbon use by eukaryotic algae. CCM activity has higher energetic requirements than diffusive CO 2 uptake, therefore when light is low, CCM activity is reduced in favour of diffusive CO 2 uptake. We hypothesized that the proportional cover of macroalgae without CCMs (red and green macroalgae) would be low (<10%) across four sites in Tasmania, southern Australia at two depths (45 and 1214m); the proportion of species lacking CCMs would increase with decreasing depth; the δ 13 C values of macroalgae with CCMs would be more depleted with depth. We found the proportion of non-CCM species ranged from 0 to 90% and included species from all three macroalgal phyla: 81% of red (59 species), 14% of brown (three species) and 29% of green macroalgae (twospecies). The proportion of non-CCM species increased with depth at three of four sites. 35% of species tested had significantly depleted δ 13 C values at deeper depths. Non-CCM macroalgae are more abundant in some temperate reefs than previously thought. If ocean acidification benefits non-CCM species, the ramifications for subtidal macroalgal assemblages could be larger than previously considered.