Dataset: Community composition of corals in Palau determined by quantitative transects sampled in April 2023

In this study, we took a multi-pronged approach to understand recruitment and life-history bottlenecks on coral reefs in Palau. Recruits in our study were corals collected on settlement tiles. Because tiles were deployed for intervals of weeks to months, all recruits in this study were < 6 months post-settlement. Juveniles were corals ≤ 5 centimeters (cm) in diameter observed using macro photography. While precise ages cannot be estimated, most corals < 5 cm are likely ≤ 3 years old. Adults were corals > 5 cm in diameter, including many large colonies observed using photography.

Settlement panels made from terra cotta (2018-2022) or limestone (2022-2023) were deployed at each site to collect coral recruits. Tiles were 15 x 15 cm and attached to stainless steel threaded rods embedded in the reef using clamps or zip ties. In 2018, tiles were deployed for the duration of a 2-week field season. In 2021-2023, tiles were deployed during one field season and recovered during the subsequent field season, ~6 months later. Tiles were examined using a dissecting microscope immediately following recovery. All coral recruits were photographed, removed with a razor blade, and individually preserved in 1.5 milliliters (mL) of 95% ethanol. Photographic surveys were undertaken using two methods: (1) a qualitative biodiversity survey (2021-2022) and (2) quantitative transects (April 2023).

For the biodiversity survey, adult and juvenile corals were selected haphazardly for sampling by 2 to 4 investigators during a 45- to 60-minute SCUBA dive. The goal of the biodiversity survey was to photograph every species present at a site, so species were not photographed in proportion to their occurrence. The freeform style of the biodiversity survey allowed cryptic spaces to be investigated so a maximum number of species was observed. See "Related Datasets" for the biodiversity survey data.

For the quantitative transects, all adult and juvenile corals within 0.5 meters (m) on either side of a 10-m transect were photographed (i.e., each transect represents 10 square meters). Adult corals were photographed from an altitude of ~1 m, including overlapping photos along the length of the transect. Juvenile corals were photographed individually with detailed investigation of cryptic spaces along each transect. The quantitative transect data are included in this dataset. All transects were sampled in April 2023.

Photographs were recorded using an Olympus TG-6 camera and a DSLR camera (Nikon D850) with wide-angle (adults) and macro (juveniles) lenses. Images from the biodiversity survey (n=2583 images) and the quantitative transects (n=1858 images) were viewed individually. All corals in each image were identified to genus level by reference to taxonomic guides. Coral recruits from settlement tiles were identified using the ITS2 locus. Each recruit was individually crushed with a sterile razor blade, and DNA was extracted using Chelex resin (Bio-Rad, 2018-2022) or the HotSHOT method (Truett). PCR was used to amplify the ITS2 locus, and successful PCR products were sent for Sanger sequencing (Sequegen, Worcester, MA). Sequences were compared to published sequences in GenBank using the blastn algorithm.