Table of Contents

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

Data are from experiments performed across multiple sites in Israel, Saudi Arabia, and Djibouti. Multiple ramets from seven genets of Acropora hemprichii, Pocillopora verrucosa, Porites lobata, and Stylophora pistillata were collected from six sites along the Red Sea and used in an 18-hour acute thermal stress assay using the Coral Bleaching Automated Stress System (CBASS). 

Corals were subjected to 18-hour acute thermal profiles with four peak target temperatures (30°C, 33°C, 36°C, and 39°C). Experimental tanks were ramped up from the 30 degrees Celsius control treatment to temperature treatments reaching 33°C, 36°C, and 36.5°C in the prolonged experiment at rates of 0.5 and 1.5 degrees C per day. Each temperature treatment contained two replicate tanks (A and B).

Chlorophyll a and symbiont densities as physiological response metrics were recorded and at the end of the experiments. A MicroDisTec homogenizer 125 (Thermo Fisher Scientific), SpectraMax Paradigm Multi‐Mode Microplate Reader (Molecular Devices), and flow cytometer (BD LSRFortessa, BD Biosciences) were used.

'Chla_cm2' refers to chlorophyll a extracted from algal symbionts extracted in each ramet, normalized to the surface area of the ramet (µg per cm²). 'Sym_density' refers to symbiont densities measured in each ramet, normalized to the surface area of the ramet (cells per cm²).

Problems/Issues:
There are some missing data due to sample loss or mortality.

Data Processing:
Data were organized using Microsoft Excel and R statistical software (version 4.0.3).

Code used to analyze and plot data is available on GitHub: https://github.com/BarshisLab/Gradient-physiology.

BCO-DMO Processing:
- Adjusted field/parameter names to comply with BCO-DMO naming conventions;
- Added a conventional header with dataset name, PI names, version date;
- Converted Collection_Date to YYYY-MM-DD format.

Originally submitted GitHub repository https://github.com/BarshisLab/Gradient-physiology was forked to https://github.com/BCODMO/Gradient-physiology/tree/v1.0 for curation purposes and tagged with release 1.0, which corresponds with this dataset submission. The code is attached to this record as a Supplemental File. Note the original repository may have continued updates.

NSF Award Abstract:
The past few years have seen an unprecedented amount of coral bleaching across the globe. Global bleaching events in 2015-17, severely impacting iconic coral reefs in places such as the Great Barrier Reef, Micronesia, Hawaiian Islands, and Caribbean, were the worst recorded in recent human history. When ocean temperatures rise, the symbiosis between reef-building corals and their photosynthetic algae deteriorates, many times resulting in widespread coral die-offs as corals can starve without their symbiotic partners to supply food. These widespread events can have drastic impacts on ocean health and biodiversity, as well as the communities that depend on reefs for fishing, tourism, and protection from storms. Importantly, some corals resist or recover from bleaching better than others. Such variability in coral response to ocean warming could be critical to reef survival in the future, yet the scientific community lacks any standardized diagnostics to rapidly assess bleaching tolerance limits. Here, we plan to: 1) develop a standardized, short-term exposure to assess bleaching limits (analogous to cardiac stress tests for humans), 2) design an experimental system capable of delivering a range of thermal treatments as an open-source, low-cost, highly-portable device that can be readily adapted for bleaching tests in a wide variety of coral habitats, and 3) disseminate the results, instructions, and technologies to the reef research and conservation community through a combination of hands-on workshops, online outreach materials, press releases, and open-access research publications. Widespread dissemination of project products will be achieved via hands-on demonstrations and workshops in key geographic areas (Middle East, Caribbean, and Indo-Pacific), with a focus on the assembly of the system and operation of the experimental assay using local corals. This project will train both graduate students and a postdoctoral researcher, and brings together a team of national and global researchers in a collaborative investigation to address the international problem of coral bleaching.

With each passing year, coral bleaching has shifted from an issue of serious sporadic concern to a critical widespread threat to reefs across the globe that is increasing in frequency and severity. However, during widespread bleaching events, some scattered corals and reef sections are able to survive better than others. Whether this is due to acclimatization or adaptation in thermal stress tolerance, this variability in response is critical to coral resilience to climate impacts. Currently, the scientific community lacks a standardized approach to rapidly assess coral thermal limits and identify resilient individuals or populations. Present day approaches range from observational surveys of natural bleaching and mortality, to multiple weeks of controlled chronic thermal exposure, to rapid, single or multi-day acute heat shocks. To what degree bleaching response varies across short-term versus longer-term experiments and how these responses compare to natural bleaching patterns is largely unknown. Using a group of coral species representative of a historical range of bleaching susceptibility (e.g., Acropora hemprichii, Pocillopora meandrina, and Porites lobata), research will address this important knowledge gap by experimental evaluation of the bleaching response to acute (0 - 2 day) versus chronic (>4 week) thermal stress. The overarching questions for this study are: how are the acute and chronic coral bleaching responses related, and can investigators predict ecologically relevant bleaching outcomes from the response to a short-term, acute heat-stress? To answer these questions, the research team will: 1) objectively compare acute versus chronic heat-stress exposures and synthesize a variety of response metrics based on core physiological measurements to develop a standardized, short-term thermal assay and diagnostic approach to rapidly assess bleaching, 2) operationalize an experimental system built around an open-source, cost-effective, easily transportable temperature control technology, and 3) distribute the results, experimental procedures, and temperature controlling technologies to the reef research and conservation communities. This project will produce an affordable experimental system and short-term diagnostic capable of determining coral thermal limits in just a few days in almost any location with reliable access to seawater and electricity or a portable generator. The research fills a critical knowledge gap through the development of a standardized set of diagnostic tools to assess coral thermal vulnerability before widespread bleaching events actually occur, so that proactive conservation and management strategies can be implemented ahead of widespread impacts to reef ecosystems.

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.