Table of Contents

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

Study location:
This study was conducted across eight sites at Heron Island, southern Great Barrier Reef (23°27’ S 151°55’ E), previously characterized in detail (Brown et al. 2018, 2020). Briefly, sites included each geomorphological habitat of Heron Reef: reef slope, reef crest, reef flat, shallow lagoon, and deep lagoon (Phinn et al. 2012) (Fig. 1 of Brown et al. 2023). The geomorphological habitats of Heron Reef are distinguished by diverse benthic communities, with hard coral cover higher within the reef slope and macroalgae cover greater within the lagoonal habitats (Brown et al. 2018; Roelfsema et al. 2021). Reef-wide coral cover in 2015 and 2016 was amongst the highest observations in the past 60 years (Connell et al. 1997; Brown et al. 2018; Roelfsema et al. 2021) (e.g., ~75% within the south-west reef slope and ~20% within lagoon), making these years optimal as a recent baseline record.

Within the reef slope habitat, four sites were established: two within the north-east section of the reef (Fourth Point, 4.2 meters (m) and 8 m) and two within the south-west (Harry’s Bommie, 6.1 m and 8.2 m) (Fig. 1 of Brown et al. 2023). The northeast of Heron Reef is the exposed side, subject to extreme wave forces during cyclones, whereas the south-west is sheltered from waves generated by both the south-east trade winds and extreme wave action of cyclones (Connell et al. 1997). One site was established in each other geomorphological habitat, with each site sharing its name: Reef Crest (RC; 0.9 m), Reef Flat (RF; 0.7 m), Shallow Lagoon (SL; 1.3 m) and Deep Lagoon (DL; 2.6 m) (Fig. 1 of Brown et al. 2023). Inside the lagoon, semidiurnal tidal fluctuations result in higher variability in temperature and pH than reef slope sites (Brown et al. 2018; Cyronak et al. 2020) (Fig. 2, Fig. S1 of Brown et al. 2023). Photosynthetically active radiation (PAR; µmol quanta m⁻²s⁻¹) is lower within reef slope habitats (HB5: 75.9, HB8: 72.8, FP5: 179.4, FP8: 58.9) than within the lagoon habitats (RC: 199.2, RF: 371.7, SL: 201.8, DL: 198.8), due to differences in depth (Brown et al. 2018; Cyronak et al. 2020). Mean depth and PAR were determined by use of Conductivity Temperature Depth (CTD) units that continuously recorded between July 2015 and November 2016 (SBE 16plus V2 SEACAT fitted with an auxiliary PAR sensor, Satlantic/ECO-PAR sensor) (see Brown et al. 2018 for more detailed methodology).

Evaluation of thermal stress:
Seawater temperatures were recorded at hourly intervals using cross-calibrated HOBO Pendant loggers (UA-001-64; ± 0.552 degrees Celsius (°C) accuracy) between September 2019 and August 2020. Logger accuracy was assessed at the end of the deployment period using a water bath (Thermo Scientific Precision TSGP20). Due to logger failures, only a partial temperature record was obtained at HB8 (from December 2019), RC (from February 2020), and DL (from February 2020) and there is no temperature record at FP5 (Table 1, Fig. S1 of Brown et al. 2023). No loggers were deployed at FP8 during 2019-2020.

Seawater temperatures recorded in 2019-2020 were compared to temperatures recorded at the same locations in 2015-2016 (see Brown et al. 2018 for detailed methodology). The mean, maximum, minimum, and mean daily amplitude were calculated at each site for the two periods September 2015 to August 2016 and September 2019 to August 2020 (Table 1 of Brown et al. 2023). Daily (24-hour) mean temperatures (T) were extracted from the logger data. The climatological maximum monthly mean (MMM) of Heron Reef is 27.3°C (Weeks et al. 2008). Temperature anomalies, or ‘hotspots’ (HS), were calculated from the logger data using U.S. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch (CRW) methodology (Eakin et al. 2010). If T, representing the daily mean temperature, exceeded the region's coral bleaching threshold (MMM + 1°C; 28.3°C), then the MMM was subtracted from T. Importantly, we did not use nighttime-only temperatures, as is done with NOAA CRW, instead choosing to use 24-hour mean temperatures due to the diel variability across sites. Thermal anomalies were then summed across a rolling 12-week (90-day) period to determine the extent of thermal stress in degree heating weeks (DHW; °C per week).

For more detailed information, please see:
Brown, K.T., Eyal, G., Dove, S.G. et al. (2023) Fine-scale heterogeneity reveals disproportionate thermal stress and coral mortality in thermally variable reef habitats during a marine heatwave. Coral Reefs 42, 131-142. https://doi.org/10.1007/s00338-022-02328-6

The attached Supplemental File "Coral-resilience-to-marine-heatwaves-1.0.zip" contains R notebooks with the code and analyses presented in Brown et al., 2023 (DOI: 10.1007/s00338-022-02328-6). It contains the following files:

"Heron temp data from 2015-2020.Rmd " is an R notebook that compiles all of the environmental data from 2015-2020 and plots it. The temperature data are part of this dataset.

"Brown et al. Temperature variability does not promote coral resilience to marine heatwaves.Rmd" is an R notebook that analyzes and creates the figures for the benthic community composition data in Brown et al., 2023.

The original GitHub repo for these files can be found at https://github.com/imkristenbrown/Coral-resilience-to-marine-heatwaves

- Imported the original file "All in situ temperature PAR and depth from 2015-2020 at Heron Island.xlsx" into the BCO-DMO system.
- Flagged 'NA' as a missing data value (missing data are empty/blank in the final CSV file).
- Removed the first column (row count).
- Created a column for ISO 8601 date-time in UTC.
- Converted the AEST date-time column to ISO 8601 format.
- Created columns for Latitude and Longitude using the site locations provided as part of the metadata.
- Saved the final file as "918182_v1_heron_isl_temp_2015-2020.csv".

NSF Award Abstract:
Coral reefs are incredibly diverse ecosystems that provide food, tourism revenue, and shoreline protection for coastal communities. The ability of coral reefs to continue providing these services to society is currently threatened by climate change, which has led to increasing ocean temperatures and acidity that can lead to the death of corals, the animals that build the reef framework upon which so many species depend. This project examines how temperature and acidification stress work together to influence the future health and survival of corals. The scientists are carrying out the project in Hawaii where they have found individual corals with different sensitivities to temperature stress that are living on reefs with different environmental pH conditions. This project improves understanding of how an individual coral's history influences its response to multiple stressors and helps identify the conditions that are most likely to support resilient coral communities. The project will generate extensive biological and physicochemical data that will be made freely available. Furthermore, this project supports the education and training of undergraduate and high school students and one postdoctoral researcher in marine science and coral reef ecology. Hands-on activities for high school students are being developed into a free online educational resource.

This project compares coral responses to acidification stress in populations experiencing distinct pH dynamics (high diel variability vs. low diel variability) and with distinct thermal tolerances (historically bleaching sensitive vs. tolerant) to learn about how coral responses to these two factors differ between coral species and within populations. Experiments focus on the two dominant reef builders found at these stable and variable pH reefs: Montipora capitata and Porites compressa. Individuals of each species exhibiting different thermal sensitivities (i.e., bleached vs. pigmented) were tagged during the 2015 global coral bleaching event. This system tests the hypotheses that 1) corals living on reefs with larger diel pH fluctuations have greater resilience to acidification stress, 2) coral resilience to acidification is a plastic trait that can be promoted via acclimatization, and 3) thermally sensitive corals have reduced capacity to cope with pH stress, which is exacerbated at elevated temperatures. Coral cells isolated from colonies from each environmental and bleaching history are exposed to acute pH stress and examined for their ability to recover intracellular pH in vivo using confocal microscopy, and the expression level of proteins predicted to be involved in this recovery (e.g., proton transporters) is examined via Western blot and immunolocalization. Corals from each pH history are exposed to stable and variable seawater pH in a controlled aquarium setting to determine the level of plasticity of acidification resilience and to test for pH acclimatization in this system. Finally, corals with different levels of thermal sensitivity are exposed to thermal stress and recovery, and their ability to regulate pH is examined over time. The results of these experiments help identify reef conditions that promote coral resilience to ocean acidification against the background of increasingly common thermal stress events, while advancing mechanistic understanding of coral physiology and symbiosis.

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.