Barbara S. Labbe1, Damon Britton1, Lennart T. Bach1, John Beardall and Catriona L. Hurd1
1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia
2School of Biological Sciences, Monash University, Clayton, VIC, Australia
The absorption of CO2 by the oceans is causing a significant reduction in pH (0.3-0.4 units), a process known as ocean acidification (OA). Decreasing pH also alters the seawater carbonate chemistry, changing [H+], [CO2], [HCO3–] and [CO3-2], each of which can differentially, affect marine ecosystems in a complex way. For most seaweeds, dissolved CO2 is the main inorganic carbon (Ci) source for photosynthesis, as it readily diffuse into the algal cell. At the current seawater pH (7.9-8.1) CO2 represents only 1% of the total DIC (Disolved Inorganic Carbon), while 91% is HCO3–, which cannot passively diffuse through the plasma membrane. Seaweeds (~70%) have developed specialized Ci uptake mechanisms (CCM) to actively aquire HCO3– from the SW bulk and increase the [CO2] and reduce carbon limitation. However, ⁓30% of seaweeds do not have a CCM, that is, they exclusively use CO2 to carry out photosynthesis. Tasmania is globally unique as it has the largest number of non-CCM species reported, especially red algae (Rhodophyta) (90%), but, on the responses of non-CCM species to OA are scarce. The aim of this research is expand knowledge about the mechanisms by which Tasmanian red seaweeds acquire Ci and examine the effects of the different components of the seawater carbonate system (CO2, H+, HCO3–) on their physiology. The PhD is divided into four work chapters: i) CCM determination for red seaweeds, ii) Direct carbon uptake in non-CCM species, iii) CCM modulation by light, iv) Sensitivity to [H+].