This dataset includes tissue metrics of the coral species Porites astreoides and Montastraea cavernosa from Bermuda that were exposed to a temperature reduction experiment for 37 days. Prior to the experiment, 8 corals were collected with a hammer and chisel on 16th June 2019 in 5 m depth at Sea Venture Shoals, Bermuda [32º22'53” N, 64º38'11” W], which is an exposed reef featuring a typical Bermuda reef community. Water temperature during collection was ~27°C. The seasonal temperature range of Bermuda reefs is ~19°C to 29°C. The laboratory-based experiment took place at the Bermuda Institute of Ocean Sciences from 1st July to 6th August 2019 and used flow-through seawater from the adjacent Reach. Light was provided by Indoor grow lights, Sun Blaze T5 Fluorescent 44. The successive treatments were: (i) constant control temperature at 28°C, and (ii) temperature reduction (0.5 °C/day) followed by constant temperature for 20 days at 24 °C and (iii) temperature reduction (0.5 °C/day) followed by constant temperature for 20 days at 20 °C. Tissue metrics were measured on day 1, 17 and 37 of the experiment and standardized to coral surface area (determined via photography and the software ImageJ). These are total biomass (determined gravimetrically with a high precision balance (R160 P, Sartorius, Germany)), coral host biomass, zooxanthellae biomass, zooxanthellae density (Neubauer hemocytometer), and concentration of light harvesting/photo-collecting pigments (chlorophyll a + peridinin + chlorophyll c2) and concentration of photo-protective pigments (diadinoxanthin + diatoxanthin) determined with a high performance liquid chromatography Agilent 1100, Agilent Technologies, Germany. Light-harvesting pigments are also standardized to zooxanthella cell.

Sample IDs indicate species (M=Montastrea cavernosa, P= Porites astreoides), the replicate ID (1 to 8; each replicate is a different coral colony) and the fragment ID (A-G; each coral colony was divided into 7 fragments).