Dataset: Stress responses of cryptic corals

Colonies resembling the gross morphology of Porites lobata Dana, 1846 were tagged at six sites, at the Rock Islands of Palau, in November 2021 in a transect along the shoreline (N=15 per site, 90 colonies total). All colonies were sampled using a hammer and chisel between 1 and 6 meters (m) depth, with the majority between 3 and 4 m. All selected colonies were at least 1-5 m apart to reduce the risk of sampling clone mates while maximizing the probability that the colonies were exposed to similar conditions within a site. Targeted colonies were also relatively small in size (30-50 centimeters (cm)) to facilitate transportation to aquarium facilities for further analyses and experiments. The total area over which corals were collected was 250-500 square meters (m²) per site. Tissue samples were taken from the center of each colony, immediately fixed in ethanol, and stored at -20 degrees Celsius (°C) (2 × 2 cm samples). Samples were transported to Boston University where 2bRAD sequencing was conducted to resolve host genetic lineage.

In April 2022, fragments from massive Porites colonies representing three cryptic lineages were collected from the tagged coral colonies described above and transported to the Palau International Coral Reef Center for a controlled thermal stress experiment. The 25-day thermal challenge consisted of a control treatment held at ~29.5 °C and a heat-stress treatment in which temperatures were raised ~3 °C over seven days, held for 12 days, and then increased by an additional ~1 °C to simulate an acute heatwave. Each colony contributed replicate fragments to both treatments. Maximum photochemical efficiency of photosystem II (Fv/Fm) was measured daily or semi-daily following >90 minutes dark acclimation using pulse-amplitude modulated (PAM) fluorometry to assess symbiont photophysiological stress. Coral fragments were photographed with a color standard at six timepoints, and bleaching severity was quantified as changes in grayscale intensity (paling) using ImageJ. Fragment survival was monitored throughout the experiment and analyzed using Kaplan-Meier survival estimates. Lineage- and treatment-specific responses in Fv/Fm, bleaching, and mortality were evaluated using linear mixed-effects models with colony identity as a random effect to account for repeated measurements.