Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Data Files
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Project Information
• Funding

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.

Four genera were excluded from analysis because their small body size and reliance on asexual reproduction made it impossible to differentiate adults from juveniles in our dataset. The 4 excluded genera were: Cycloseris, Cynarina, Parascolymia, and Trachyphyllia.

- Created a site locations table, "site_locations.csv", using the site latitudes and longitudes provided by PI by email.
- Converted latitude and longitude values from degrees and decimal minutes to decimal degrees, and rounded to 5 decimal places.
- Imported original file "Recruit_transects.csv" into the BCO-DMO system.
- Added columns for Latitude and Longitude to the primary data table by joining to the site locations table.
- Removed the "Location" and "Abbrev" columns as requested by PI.
- In Type column, replaced "Outer" with "Classical" and "Inner" with "Extreme", as requested by PI.
- Unpivoted the table to create a new column for "Genus" and a column for "Abundance".
- Saved the final file as "926379_v1_community_comp_palau_transects.csv".

NSF Award Abstract:
Coral reefs host thousands of marine species, help protect coastlines from storm damage, generate tourism, and house fish used for human consumption. However, corals are vulnerable to increasing water temperatures, which can lead to coral death. One way for reefs to survive in warming oceans is for corals that are well-suited to warmer waters to repopulate reefs that have less temperature-tolerant individuals. For this strategy to succeed, however, the more temperature-tolerant corals need to be able to disperse to and survive in these different environments. This project takes advantage of reef systems in the Pacific nation of Palau that naturally experience a wide range in temperatures across short geographic distances. Using cutting-edge ecological and genomic techniques, the team of investigators is directly testing whether young corals from Palau’s warmest reefs can successfully be carried by ocean currents to Palau’s currently cooler reefs and subsequently survive and thrive in these habitats. Given the relevance of this research for the local ecology, the team is disseminating results to the Palauan government through a written report in conjunction with Palauan scientists who are interning with the team, and to the Palauan people through public presentations. As part of this work, the investigators are maintaining a blog and are organizing a music-lecture series combining dance, music, and science to promote awareness of the coral reef crisis across English and Spanish-speaking communities in the US. Results from this project are informing restoration and conservation practices of the Coral Conservation Consortium as well as other efforts worldwide.

A major question in evolutionary biology is how plasticity and adaptation interact to influence survival under novel environments. Understanding these processes is increasingly important as rising temperatures associated with climate change influence species globally. For marine organisms with pelagic larval phases, including reef-building corals, the post-settlement period constitutes a critical bottleneck for adaptation and plasticity, with the added complexity that the conditions experienced and time spent as larvae can incur carryover effects. This project leverages reefs in Palau that span a steep environmental gradient to study how environmental variation drives selection and plasticity and to examine if dispersal between reefs limits success across habitats due to carryover effects. The investigators are testing the overarching hypothesis that corals from warmer and more variable environments are adapted to warmer temperatures and exhibit increased plasticity, but that dispersal between reefs incurs a fitness cost. The team integrates field and molecular techniques to: 1) investigate the degree of selection occurring on warmer and more variable reefs, 2) test whether corals transplanted to more variable environments improve their thermal tolerance through developmental plasticity, and 3) examine whether delays in metamorphosis required for dispersal across reefs comes at a fitness cost due to carryover effects.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.