Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
• Data Files
• Supplemental Files
• Parameters
• Instruments
• Project Information
• Funding

Coral adults were collected from a reef called Taoch (7 16.033 N, 134 23.233 E), spawned in the lab at the Palau International Coral Reef Center, and settled on tiles. We then outplanted the tiles at Taoch (same coordinates) and a nearby reef called Outer Taoch (7 16.232 N, 134 22.999 E).

We conducted an experiment to determine whether post-settlement survival differs between corals settling on their natal (home) extreme reef or at a classic (away) reef.  Adult massive Porites corals were collected from six sites in Palau immediately prior to their spawning season in April 2023. Corals were either whole colonies or fragments of large colonies removed with a hammer and chisel (15 – 30 cm diameter). Collected corals were held in individual plastic containers (4.2 L; 17 x 13 x 19 cm) in ambient unfiltered flow-through seawater tanks at the Palau International Coral Reef Center (PICRC). At sunset, water levels in flow-through tanks were lowered to ~15 cm so that each colony was isolated in its individual container, maintaining gametes separate until fertilization. Sperm was collected directly from male colonies using a large plastic pipette during release, and eggs were collected by pipette or by scooping from the surface with a clean petri dish. Porites gametes from 3 males and 2 females were used in a bulk cross in April 2023. Two different crosses were conducted, with one male differing between the two crosses, but larvae were pooled for the experiment. One hour after fertilization began, embryos underwent a series of dilutions with 5 µm filtered seawater (FSW) and gently split into multiple containers filled with 5 µm FSW to dilute any remaining sperm and prevent polyspermy. Two days post fertilization (dpf), larvae were settled on limestone tiles (15 x 15 cm) with crushed crustose coralline algae (CCA) used as a cue. Tiles were maintained in individual plastic containers in flow-through seawater tanks at PICRC. Additional CCA was added to each tile on the fourth dpf to encourage additional settlement. Immediately prior to transplantation, the number of settled corals on 7 randomly-selected tiles was counted using a dissecting microscope to estimate the mean number of individuals settled on each tile (272 ± 36, mean ± SE). Nine days post fertilization, tiles were deployed to Taoch (home) and Outer Taoch (away) (n=10 tiles per site). Tiles were randomly distributed between sites and deployed in a horizontal orientation on stainless steel all-thread driven into the reef, with ~10 cm distance between the seafloor and the tile. The most densely populated side of each tile was deployed facing downward to mimic the cryptic spaces where most corals settle. Sixteen days after deployment (25 dpf), tiles were recovered and examined under a dissecting microscope to identify and count surviving individuals. The number of corals was counted on all tiles post transplantation. Light and temperature were quantified at transplant locations at each site using Hobo Pendants (Onset, Wareham, USA).

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.