Comparative response of DMS and DMSP concentrations in Symbiodinium clades C1 and D1 under thermal stress

Coral-associated Symbiodinium are known to produce dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP), two biogenic sulphur compounds that potentially play a role in the algal antioxidant system and climate regulation. Coral resistance to bleaching and oxidative stress partly depends upon the capacity of their symbionts to respond to environmental stressors, with DMS and DMSP possibly contributing to this response. Under increasing sea surface temperatures, zooxanthellate corals might dominantly associate with more thermally tolerant clades of Symbiodinium, of which the nutritional and biochemical contribution to the holobiont remains unknown. Here, the production of DMS and DMSP under increasing temperature (from 26 °C to 31 °C) was investigated over 6 days in axenic cultures of twoSymbiodinium clades (C1 and D1) that are known to exhibit different thermal tolerances. Regardless of the temperature treatment, clade C1 was a greater producer of DMS and DMSP. An increase in temperature of up to 5 °C did not substantially affect DMS and DMSP production in the thermo-tolerant clade D1. However, thermal stress induced enhanced consumption of both DMS and DMSP in the more thermo-sensitive clade C1, potentially indicating the use of sulphur compounds as antioxidants. Together, these results suggest that thermal stress differentially affects the biogenic sulphur cycle of Symbiodinium clades that exhibit different thermal tolerances, with possible consequences for reef-building corals under future climate change scenarios.