Dimethylsulfonioproprionate (DMSP) content and antioxidant capacity in the host and endosymbionts of the sea anemone Entacmaea quadricolor are influenced by the host phenotype

Dimethylsulfoniopropionate (DMSP) is a key biogenic compound in marine algae and symbiotic cnidarians. Besides its role as a precursor of the climatically active dimethylsulfide, DMSP is a putative antioxidant through its capacity to scavenge reactive oxygen species. Here, the production of DMSP concurrently with the antioxidant capacity (AOC) among the host and endosymbionts of two colour phenotypes of the sea anemone Entacmaea quadricolor, that provides essential habitat for anemonefish, was investigated for 9 days under heat stress (3.2 °C and 6.3 °C above control). Although visual signs of bleaching were observed on day 3 in all of the anemones at high temperature, cell density and chlorophyll a content did not vary among temperatures over time. The maximum quantum yield of endosymbionts decreased over time in medium and high temperature treatments in both phenotypes, indicating slight photoinhibition under thermal stress. Temperature had no or little effect on AOC and DMSP concentrations in the host and endosymbionts in both phenotypes, suggesting adaptation of subtropical E. quadricolor and associated symbionts to short-term abrupt changes in temperature, which is a regular occurrence in this region. However, host and endosymbiont AOC and DMSP concentrations were, at least partly, driven by the host phenotype, with overall greater AOC and lower DMSP concentrations being found in pink compared with green anemones. These results, along with stronger photoinhibition in the green phenotype under thermal stress suggest that green anemones could be more vulnerable to environmental pressure than the pink phenotype. As our oceans continue to warm, the differing responses of the colour phenotypes may influence their relative abundance on reefs, and have implications for reproductive success as the phenotypes correspond to different sexes. Furthermore, the selective disappearance of one phenotype could adversely affect anemonefish that preferentially associate with more sensitive colour morphs.