MEPS 559:257-263 (2016)  -  DOI: https://doi.org/10.3354/meps11916

ABSTRACT: Non-calcifying photosynthetic anthozoans have emerged as a group that may thrive under high carbon dioxide partial pressure ( pCO₂) conditions via increased productivity. However, the physiological mechanisms underlying this potential success are unclear. Here we investigated the impact of high pCO₂ on the dissolved inorganic carbon (DIC) use in the temperate sea anemone Anemonia viridis. We assessed the impacts of long-term exposure to high pCO₂, i.e. sampling in situ natural CO₂ vents (Vulcano, Italy), and short-term exposure, i.e. during a 3 wk controlled laboratory experiment. We focused on photo-physiological parameters (net photosynthesis rates, chlorophyll a content and Symbiodinium density) and on carbonic anhydrase (CA) activity, an enzyme involved in the energy-demanding process of DIC absorption. Long-term exposure to high pCO₂ had no impact on Symbiodinium density and chlorophyll a content. In contrst, short-term exposure to high pCO₂ induced a significant reduction in Symbiodinium density, which together with unchanged net photosynthesis resulted in the increase of Symbiodinium productivity per cell. Finally, in both in situ long-term and laboratory short-term exposure to high pCO₂, we observed a significant decrease in the CA activity of sea anemones, suggesting a change in DIC use (i.e. from an HCO₃^- to a CO₂ user). This change could enable a shift in the energy budget that may increase the ability of non-calcifying photosynthetic anthozoans to cope with ocean acidification.

KEY WORDS: Dissolved inorganic carbon uptake · Carbonic anhydrase · Ocean acidification · Plasticity · CO₂ vent · Anemonia viridis