Poster Australian Marine Sciences Association 2022

Accessories To The Crime Or Double Agents? Ocean Acidification And Some Irradiance Regimes May Counter The Impact Of Ocean Warming On Autotrophy In A Reef-Building Coral. (#522)

Robert A. B. Mason 1 2 , Chris B. Wall 3 , Ross Cunning 4 , Sophie Dove 2 , Ruth D. Gates 5
  1. CSIRO Oceans and Atmosphere, St Lucia, Queensland, Australia
  2. University of Queensland, St. Lucia, Queensland, Australia
  3. Division of Biological Sciences, University of California San Diego, San Diego, California, USA
  4. Daniel P. Haerther Center for Conservation and Research, Shedd Aquarium, Chicago, Illinois, USA
  5. Hawaiʻi Institute of Marine Biology, University of Hawaiʻi, Kāneʻohe, Hawaiʻi, USA

Photosynthesis of corals is dependent on optimal ranges of temperature, irradiance and seawater carbon chemistry. Greenhouse gas emissions are changing the regimes of these parameters in marine environments. If significant changes in coral autotrophy result, flow-on effects may accrue to the entire tropical reef ecosystem as corals are sources of organic carbon and calcified structure. We investigated the impacts of combined seawater warming (25–29°C), acidification (431–962 μatm pCO2), and different irradiance levels (7.5–15.7 mol photons m-2 day-1) on Pocillopora acuta, a functionally important hard coral in Hawai‘i and other parts of the Pacific. Across a range of organismal parameters (symbiont density, photosynthetic pigments, photosynthesis and respiration), elevated temperature had a clear effect on most. Responses of the host and symbiont were generally unaffected by acidification alone, however, acidification and irradiance exhibited a complex interaction with temperature to impact photosynthesis. Acidification and moderate irradiance levels ameliorated a decline in photosynthesis that would otherwise have been seen at elevated temperature. This finding suggests that the fate of corals in a warming ocean also depends upon changes in chemical and photic conditions, and may have implications for restoration methods that involve shading corals or the management of turbidity near reefs.