Location: patch reef 13 in Kāne'ohe Bay, O'ahu, Hawai'i (21.4509, -157.7954)

Study site and temperature data

This study was conducted at Patch Reef 13 (PR13) in the southern end of Kāneʻohe Bay, Oʻahu, Hawaiʻi (21.4509, -157.7954). Hourly seawater temperatures were recorded continuously from January 2014 to April 2023 from temperature sensors within the reef at PR13 (1–2.7 m depth) as well as at two adjacent locations within 0.5 km: (Brown et al., 2022) PR12 (21.45096,-157.7972; 1.5 m depth) and (Rodgers and Jokiel, 2005) the National Oceanic and Atmospheric Administration (NOAA) Pacific Marine Environmental Laboratory (PMEL) ‘CRIMP2’ buoy (21.458, -157.798; 0.7 m depth) (Brown et al., 2023 Fig. 1, Fig. S1, Table S1). Mean daily (24 hours) seawater temperatures were calculated and averaged when data sources were overlapping, and used to determine cumulative heat stress (degree heating weeks; DHW) at PR13 following the equations in (Brown et al., 2022) (Brown et al., 2023 Fig. 1, Fig. S2, Table S2). The climatic maximum monthly mean (MMM) for Kāneʻohe Bay was determined from seawater temperature data from two monitoring stations on the reefs surrounding the island of Moku o Loʻe (PR1), located approximately 2 km from the study site in the southern region of Kāneʻohe Bay: 1) NOAA’s MOKH1 Station (21.433, -157.790; 1.7 m depth) and 2) the HIMB Point Lab Weather Station (21.433, -157.7863; 1 m depth; ((Rodgers and Jokiel, 2005)). Data from 1992–2002 (excluding the 1996 marine heatwave) provided the closest available 10-year data to the time period used by NOAA for determining climatology MMM (1985–1990, 1993), resulting in a climatology MMM for Kāneʻohe Bay of 27.3°C. This MMM was used here to calculate DHW from 2014–2023. Cumulative heat stress at PR13 was compared to PR1 (21.4438, -157.7883; 1 m depth) (Brown et al., 2023 Table S1, Fig. S1). DHWs were also calculated from the temperature data recorded at both PR1 and PR13 using the MMM of 27.0°C (Main Hawaiian Island MMM as determined by NOAA and Kāneʻohe Bay climatology MMM from the 1960s (Jokiel and Coles, 1977)), and other recent MMM values used for Kāneʻohe Bay in the literature: 27.7°C (Wall et al., 2021; Jury and Toonen, 2019) and 28.0°C (Jury and Toonen, 2019; Innis et al., 2021) (Brown et al., 2023 Fig. S2).