Corals that survive repeated thermal stress show signs of selection and acclimatization

Climate change is transforming coral reefs by increasing the frequency and intensity of marine heatwaves, often leading to coral bleaching and mortality. Coral communities have demonstrated modest increases in thermal tolerance following repeated exposure to moderate heat stress, but it is unclear whether these shifts represent acclimatization of individual colonies or mortality of thermally susceptible individuals. For corals that survive repeated bleaching events, it is important to understand how past bleaching responses impact future growth potential. Here, we track the bleaching responses of 1,832 corals in leeward Maui through multiple marine heatwaves and document patterns of coral growth and survivorship over a seven-year period. While we find limited evidence of acclimatization at population scales, we document reduced bleaching over time in specific individuals, primarily in the stress-tolerant taxa Porites lobata, indicative of acclimatization. For corals that survived both b..., We used large-area imaging (photogrammetry) to capture a 3D snapshot of coral reef condition at our six sites in leeward Maui in 2014, 2015, 2017, 2019, and 2021. Large-area imaging is the process of generating a composite visual reconstruction (i.e., 3D model, orthoprojection, DEM, etc.) via the overlap of many component images. Large-area imaging has been used with increased frequency to archive coral reef structure and condition, and provides a basis for in silico field work to answer a variety of ecological questions. Details of our large-area imaging workflow are available elsewhere and will be described in minimal detail here.
At each fixed site, divers entered the water with two D7000 SLR Nikon cameras (focal lengths of 18mm and 55mm) in Ikelite underwater housings. Divers marked the boundaries of each 10 x 10 m long term monitoring plot with six calibration tiles, and placed four 0.5 m long scale bars within the plot. One diver swam approximately 1.5 m over the reef in a gridded..., , # Corals that survive repeated thermal stress show signs of selection and acclimatization

[https://doi.org/10.5061/dryad.9cnp5hqsf](https://doi.org/10.5061/dryad.9cnp5hqsf)

## Coral tracing data and file structure

One CSV file containing raw data is included (All_sites_bleaching_by_genet.csv). It contains data on nearly 2,000 corals that were traced and followed over time using large area imagery. Corals are from six sites in leeward Maui, surveyed in 2014, 2015, 2017, 2019, and 2021. Corals were exposed to thermal stress that caused widespread bleaching in 2015 and 2019.

Fields in the CSV file are as follows:

* ind: A unique identifier for each genet. Generated by concatenating the site name, species name, and genet number
* TagLab.Date: The year in which the coral was surveyed (2014, 2015, 2017, 2019, or 2021)
* genet: An integer ID number associated with an individual coral (or genet) for a given site. A new sequence of integers created for each site and taxa (for example,...