Heat-evolved microalgal symbionts increase thermal bleaching tolerance of coral juveniles without a trade-off against growth

This study was designed to test the effect of heat-evolved macroalgal symbionts against bleaching tolerance in juvenile corals in response to a simulated heatwave.

Juveniles of the coral Acropora tenuis were infected with either wildtype (WT10) or heat-evolved (SS1 or SS8) strains of the Symbiodiniaceae species Cladocopium C1acro (formerly Cladocopium goreaui 2–4).

The juveniles were maintained at ambient conditions (27°C) for 10 months at which time their size was measured. Growth, survival, and metabolism data were collected following a simulated heatwave (31°C for 41 days).

Photographs and PSII maximum quantum yields (Fv/Fm) were collected throughout the heat stress period, stable isotope incubation and cell counts were carried out on day 39, and respirometry on days 40-41. Symbiodiniaceae cell densities per juvenile were quantified to assess bleaching.

Statistical analyses were run in R and respirometry data was analysed using the respR package.

Full methods and technical details are found in the paper https://ssrn.com/abstract=3981099