Interactive effects of ocean acidification and elevated temperature on seaweed physiology
Francisco J. L. Gordillo
Departamento de Ecologia, Universidad de Malaga, Spain
Seaweeds are the major primary producers of the Arctic coastal ecosystems. A significant part of the food web, both aquatic and terrestrial depend on the biomass production of these organisms. Temperature is a well known abiotic factor determining biogeographic distribution of seaweeds, but little is known on how the increase in CO₂ may modify the response of seaweeds to increased temperature. Our group aims to elucidate the mecanisms involved in the acclimation to the new environmental scenario the seaweeds are facing. Metabolic processes such as inorganic carbon utilisation have been revealed as acting in a different way in Arctic seaweeds than in their cold-temperate counterparts. In non-polar species, one of the major enzymes involved in inorganic carbon acquisition, the external carbonic anhydrase (eCA) is known to be repressed under high CO₂. However, Arctic seaweeds show high values of eCA activity and seem to be little affected by CO₂, so that eCA might have evolutively changed as part of the adaptation to low temperature. Other processes involved in the carbon balance of the organisms are photosynthesis and organic carbon release to the external medium. The release of organic carbon acts as a regulatory mechanism for internal C:N balance, so that differences in inorganic carbon utilisation (acquisition and photosynthesis) may lead to a different proportion of primary production lost as organic C. As a consequence, the acclimation of seaweeds to changing CO₂ and temperature would change the C balance of the thalli, so affecting the biogeochemical cycle of C. These responses are highly species-specific, with species taking advantage of the new scenario and others suffering an adverse effect. Changes in both the C balance and species dominance/composition may propagate to other trophic levels, potentially changing the whole ecosystem.