Dataset: Coral surveys

Palau and Yap:
Corals were classified to the species level, or to the highest resolution possible, especially for massive Porites and encrusting Montipora colonies, along 10 m long transects. All other organisms were identified to the highest resolution possible, and all inorganic surfaces were recorded. Survey depth was maintained between 2 to 5 meters to examine the potential of shallow-water reef-carbonate production. The chord length of each organism, or abiotic component, were recorded along each transect. Note that the transects followed the contour of the reef. Surveys in Palau were conducted from June 2nd to June 24th, 2017, and from June 25th to July 6th, 2017 in Yap. Codes in dataset: S = Sand R = Rubble SR = Sand & Rubble CA = Coralline algae TA = Turf algae Hal = Halimeda.

Kosrae and Pohnpei, Federated States of Micronesia (FSM):
Twenty-four study sites were randomly selected in each of Pohnpei (6.2°N, 158.2°E) and Kosrae (5.3°N, 162.9°E) FSM using a randomly stratified sampling approach with the package sp in R. In Pohnpei, reefs were stratified as inner reefs, patch reefs, and outer reefs. In Kosrae, we only stratified the reefs as either inner reefs or outer reefs (because of the lack of patch reefs). Sample size of each strata was determined by calculating the geographic area of each reef type, using the area function from the R package raster, and allocating the number of sites in accordance with the area estimates. Reef surveys focused on the 2–5 meters depth contour to estimate shallow-water carbonate production.

Six, 10 m transects, using a modified line-intercept technique that followed the reef substrate, were used to measure the benthic composition for every centimeter, at each site of the 48 sites. A few meters gap was allocated between the ends of the transects to ensure no overlap of substrate between transects. Corals were recorded to species level, except massive Porites and encrusting Montipora, which were recorded in the field as growth forms. All other organisms along each transect were identified to the highest possible taxonomic resolution. Rugosity was recorded using the planar length of a second transect that spanned across the reef horizontally. Echinoids were recorded within 30 cm on either side of the 10 m tape. The urchins were recorded as Echinometra, Diadema, and 'Other', and the diameter of each echinoid test was measured to the nearest 0.5 cm. The abundance of Acanthaster solaris (crown-of-thorns sea star) were recorded within 5 m along each of the six 10 m transects. Herbivorous parrotfishes were videoed and identified to species and their estimated length was recorded to the nearest cm along six transects, each of which was 30 m long by 4 m wide. Care was taken to record the fish-transect videos ahead of the other transects to avoid any disturbance to the fishes.

Majuro (Republic of the Marshall Islands) and Kiritimati (Republic of Kiribati):
A stratified random sampling approach was used to survey the reefs of Majuro (7.0667° N, 171.2667° E) and Kiritimati (1.8721° N, 157.4278° W), by randomly selecting 24 study sites at each island using the package 'sp' in R. In both locations, a stratified random sampling approach was used to survey the reefs for carbonate production by randomly selecting 24 sites on each island, with the exception of Kiritimati where only 22 of the 24 sites were surveyed because of inclement weather. At both locations, the sites were stratified as either (i) outer reefs, or (ii) patch reefs in lagoons. The number of sites sampled per habitat varied according to the area of available habitat at each location. The investigators were particularly interested in determining the potential of shallow-water reef carbonate production, and therefore focused surveys between 2–5 m. Majuro was surveyed from 6/17/2019 to 7/6/2019 and Kiritimati was surveyed from 7/10/2019 to 7/22/2019.