DOI: 10.5061/dryad.0vt4b8hb6
title: Data from: A long-term perspective to the effects of the 2023 marine heat wave on stony corals in the Caribbean

description: Marine heat waves (MHW) are a leading cause of death for stony corals, and
 it is reasonable to expect that a record-breaking MHW would negatively
 impact coral communities. 2023–2024 provided a test of this assertion in
 St. John, US Virgin Islands, where an intense MHW brought temperatures of
 30.6°C and degree-heating weeks of 23.23°C-weeks. On reefs where coral
 cover has been low for decades, the 2023/24 MHW did not have discernible
 effects on coral cover. Nonetheless, there was a trend between 2023 and
 2024 for mean coral cover to decline by small absolute (≤ 3%), but large
 relative (13–27%) amounts, with these changes affecting multiple genera
 and perturbing coral assemblages, especially at 14-m depth. These trends
 are eclipsed by the massive changes that have affected these coral
 communities over the last four decades; the 2023/24 MHW was the latest in
 a series of disturbances transitioning these reefs to low coral cover.
 This MHW did not statistically depress coral cover, but it changed coral
 assemblages, intensifying the ecological perils of rarity, extirpation,
 and perhaps local extinction.
description: # Data from: A long-term perspective to the effects of the 2023 marine
 heat wave on stony corals in the Caribbean Dataset DOI:
 [10.5061/dryad.0vt4b8hb6](10.5061/dryad.0vt4b8hb6) ## Description of the
 data and file structure These data were collected in support of an
 analysis of the effects of the 2023 MHW on the coral reefs of St. John ###
 Files and variables #### File: 6_Tektite_coral_cover_genus.csv
 **Description:** These data describe the percentage coral cover by genus
 at the Tektite Reef (14 m depth) in St. John from 2021-2024 #####
 Variables Year = study year from 2021 to 2024 Picture ID = unique
 reference linking data to a photoquadrat recorded in the field Quadrat =
 number of quadrats sampled each year along each transect, 1 to 10 % Cover
 = coral cover Genus = coral genus #### File:
 2_Monthly_temperature-by_site.csv **Description:** These data describe
 seawater temperature at 5 m depth at 6 sites between Cabritte Horn and
 White point (see Fig. S1) ##### Variables Date = month (1 = January, etc.)
 Day = day of month Year = 10 (2010), 11 (2011) to 23 (2023). Yawzi_Tiles =
 temperature (°C) at Yawzi Tile site (see Fig S1) Tektite_Tiles =
 temperature (°C) at Tektite Tile site (see Fig S1) Cabritte_Tiles =
 temperature (°C) at Cabritte Tile site (see Fig S1) Little_Lam_Tiles =
 temperature (°C) at Little Lameshur Tile site (see Fig S1) White_Tiles =
 temperature (°C) at White Point Tile site (see Fig S1) 999 = missing data
 #### File: 3_Random_Sites_coral_cover.csv **Description:** These data
 describe the percentage coral cover (pooled among taxa) at the five random
 sites in St. John from 1992-2024 ##### Variables Site = study site,
 Cabritte Horn, East Tektite, Europa Bay, West Little Lameshur, West
 Tektite, White Point Quadrat = number of quadrats sampled each year from 1
 up to 44 Year = study year from 1992 to 2024 % Cover = coral cover, pooled
 among taxa #### File: 4_Random_Sites_coral_cover_genus.csv
 **Description:** These data describe the percentage coral cover by genus
 at the five random sites in St. John from 2021-2024 ##### Variables Site =
 study site, Cabritte Horn, East Tektite, Europa Bay, West Little Lameshur,
 West Tektite, White Point Year = study year from 2021 to 2024 Picture ID =
 unique reference linking data to a photoquadrat recorded in the field %
 Cover = coral cover Genus = coral genus #### File:
 5_Tektite_coral_cover.csv **Description:** These data describe the
 percentage coral cover (pooled among taxa) at the Tektite Reef (14 m
 depth) in St. John from 1987-2024 ##### Variables Date = when data
 collected – month/day/year Quadrat = number of quadrats sampled each year
 along each transect, 1 to 10 Transect = transect along which quadrats are
 located, 1, 2, or 3 % Cover = coral cover nd = missing data #### File:
 7_Yawzi_coral_cover.csv **Description:** These data describe the
 percentage coral cover (pooled among taxa) at the Yawzi Point reef (9 m
 depth) in St. John from 1987-2024 ##### Variables Date = when data
 collected – month/day/year Picture ID = unique reference linking data to a
 photoquadrat recorded in the field % Cover = coral cover, pooled among
 taxa Quadrat = number of quadrats sampled each year along each transect, 1
 to 10 Transect = transect along which quadrats are located, 1, 2, or 3 %
 Cover = coral cover nd = missing data #### File:
 8_Yawzi_coral_cover_genus.csv **Description:** These data describe the
 percentage coral cover by genus at the Yawzi Point Reef (9 m depth) in St.
 John from 2021-2024 ##### Variables Year = study year from 2021 to 2024
 Picture ID = unique reference linking data to a photoquadrat recorded in
 the field Quadrat = number of quadrats sampled each year along each
 transect, 1 to 10 % Cover = coral cover Genus = coral genus #### File:
 1_Long_Term_Temperature_1989_2025.csv **Description:** These data describe
 seawater temperature off St. John, with in situ records from Great
 Lameshur Bay at 9 m depth at Yawzi Point (see Fig. S1) Instrument = logger
 used to collect date either (1) Ryan Tempmentor, (2) Hobo logger
 (U22-001), (3) SBE39, (4) nd = no data ##### Variables Date = date of
 measurement, month/day/year Temp°C = seawater temperature DHW_28.43°C =
 degree heating weeks based on a mean monthly max (MMM) of 28.43°C, note
 “999” recorded where 84 consecutive daily temperature data were not
 available due to missing logger data DHW_28.71°C = degree heating weeks
 based on a mean monthly max (MMM) of 28.71°C, note “999” recorded where 84
 consecutive daily temperature data were not available due to missing
 logger data NOAA DHW = degree heating weeks as published for the south
 coast of St. John by NOAA 999 = missing data in number columns