Effect of temperature-induced stress on dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP) in members of the Symbiodiniaceae family and the anemone Exaiptasia pallida

Coral reefs are among the most biodiverse ecosystems on Earth and they are showing a global decline due to different causes, including temperature increase caused by climate change. Corals survive thanks to the obligate symbiotic relationship between the animal host and their algal endosymbionts from the Symbiodiniaceae family. These autotrophic dinoflagellates are strong producers of dimethylsulphoniopropionate (DMSP) and dimethylsulphide (DMS) which are important in global climate, because they assist with the formation of cloud condensation nuclei and temperature homeostasis. Chapter Two focuses on the DMSP concentration in the coral Porites astreoides and macroalgae that grow in its proximity, giving an insight of DMSP-production potential along future tropical coasts where corals might be replaced by macroalgae. The following chapters use two clonal isolates of the model anemone Exaiptasia pallida (strains CC7 and H2) and their respective Symbiodiniaceae species (Symbiodinium linuchae and Breviolum minutum) in a laboratory setting. Chapter Three reports a short-term experiment on increased temperature and showed that anemones bleach at 34C, but unlike previous research DMSP/DMS did not increase in stress conditions, it decreased instead. Chapter Four describes the development of bio-imaging techniques to quantify the actual Symbiodiniaceae loss within the anemones over the same temperature profile as in Chapter Three. It was confirmed that both anemone species suffer significant algal symbiont loss. Experimentation described in the final data chapter subjected the organisms to a more realistic temperature increase. Anemones did not withstand the increased temperature as well their algal symbionts and started to die off after the temperature reached 32C. The concentration of DMSP and DMS in both experiments was closely related to the numbers of Symbiodiniaceae present in the anemones, and also in this occasion it did not increase with stress. This thesis highlights the decrease of DMSP/DMS concentration in both algae and anemones at high temperature stress and advances our understanding of these organisms’ behaviour in a warming planet.