Satellite sea surface temperature observations to monitor marine heatwaves for improved ocean management

Australia’s extensive coastline hosts diverse marine habitats that support the economy, communities, and culture. As our oceans warm under climate change, marine heatwaves are projected to increase in severity, duration and frequency. These events can cause species mortality, distribution shifts, disease, and coral bleaching. Given the consequences for ecosystems, industries, and communities, near real-time thermal stress monitoring around Australia is critical for effective management. Advances in satellite technology have made it possible to monitor sea surface temperatures (SST) globally on a sub-daily time scale. These observations underpin marine science, climate modelling, and management.

The Great Barrier Reef (GBR) is the world’s largest coral reef system stretching over 2900 km. It hosts around 9,000 marine species, including corals and fish. When ocean temperatures exceed species’ optimal ranges, organisms experience thermal stress. For example, elevated ocean temperatures are the most common cause of widespread coral bleaching, and if they persist long enough, can result in coral mortality. Elevated ocean temperatures can also impact species growth, health and distributions, affect reef biodiversity and disrupt food webs and fisheries. Mass coral bleaching events were recorded on the GBR in 2016, 2017, 2020, 2022, 2024 and 2025. Satellite-derived SST information has been used on the GBR to monitor thermal stress at reef scales and inform reef management decision-making for over a decade.

This capability has been extended recently to the entire Australian region. AusTemp is a new remote sensing application, providing near real-time daily high resolution (2km scale) SST information for Australian waters. It provides near real-time thermal stress and marine heatwave monitoring across Australian waters. AusTemp enables users to track marine heatwaves as they evolve.

AusTemp will support fisheries, conservation, reef management and aquaculture across Australian waters. Because marine heatwave impacts are often localised, high-resolution information is critical for targeted monitoring and response. The ability to compare temperatures observed today with those in the past is invaluable for managers when assessing potential impacts of conditions on stocks or ecosystems. Combining AusTemp with other ocean observations in one interface further improves usability.

For a fishery manager, this information can help explain why stock distributions are shifting or catchability is altered. For aquaculture operators, it can provide context for disease outbreaks or mortality events. For conservation managers, it helps identify emerging hotspots of stress and enable better location targeting for monitoring or remediation efforts. By enabling early detection of increased thermal stress, AusTemp can improve operational decision making and climate resilience planning. This capability is increasingly critical as marine heatwave impacts intensify and costs escalate in a rapidly warming ocean.

Satellite monitoring provides near real-time thermal stress updates across the GBR. For more than a decade, reef managers relied on a system called ReefTemp to monitor sea surface temperatures on the GBR. ReefTemp was used to guide aerial bleaching surveys, brief ministers and agencies during extreme summers and prioritise reef monitoring when resources were limited. As marine heatwave impacts spread beyond the GBR, a national system became necessary.

AusTemp is a new remote sensing application for Australia developed through a collaboration between the Bureau of Meteorology, the Integrated Marine Observing System (IMOS) and the Australian Ocean Data Network (AODN). It builds directly on the legacy of ReefTemp and is providing critical information to managers needing clearer, faster answers in a warming ocean.

Reef authorities, scientists from the Australian Marine Institute of Science (AIMS), fisheries agencies, and operational modellers provided feedback throughout development, improving AusTemp's ability and application. Feedback helped address stress-estimation issues and inconsistent messaging between prototypes. Next steps involve calibration of metrics with ecological observations, upgrading established relationships based on past conditions with those more applicable to a warmer ocean. This collaborative approach has ensured AusTemp is not just scientifically robust, but operationally usable.

AusTemp is delivered by AODN through THREDDS and IMOS Live (https://imoslive.aodn.org.au). It provides:

Heat stress monitoring metrics DHD is specifically designed to track coral bleaching risk, while the MHW categories provides a broader assessment of oceanic heat stress. It is not seasonally constrained and can occur at any time of year, at any location, making it relevant to a wider range of marine ecosystems and species.

AusTemp captures local warming patterns that coarser products may miss. It provides finer-scale temperature maps, improved coverage in cloudy regions, and clearer local gradients. For users, the greatest impact is easy access to critical information in real time at reef scales at their fingertips during MHW events. It helps users explain observed changes and justify decisions using trusted information.

MHWs do not follow calendar seasons. They can occur in winter, affect temperate species, and trigger cascading impacts through marine food webs. AusTemp enables users to move beyond simple detection by allowing them to track heatwave intensity, compare events across regions and years, and assess cumulative exposure.

AusTemp supports fisheries, aquaculture, and conservation by helping explain stock shifts, disease or mortality events, and emerging hotspots of ecosystem stress.

It also informs concrete management actions. Survey planning is strengthened by allowing managers to prioritise monitoring in regions experiencing persistent heat stress, rather than relying on anecdotal observations. Risk communication is improved through clear, categorical marine heatwave information that conveys urgency to non-technical audiences. Early warning capability supports proactive response planning, from temporary management closures to targeted research or intervention campaigns.

The 2024 GBR summer demonstrated the value of fast, trusted, fine-scale thermal stress monitoring. As SSTs climbed across the southern GBR from late December 2023, satellite-derived Degree Heating Days accumulated through January and February. When heat stress crossed bleaching thresholds around the Keppel Islands and Capricorn-Bunker reefs, managers launched aerial surveys in late February 2024, before bleaching was widely visible from the water. The results triggered reef-wide aerial assessments across the GBR Marine Park in March. By the time heat stress peaked, some southern inshore reefs had recorded the highest satellite-era thermal stress values observed on the GBR, and nearly three-quarters of surveyed reefs showed bleaching consistent with the mapped heat-stress footprint. The maps told managers where to look and when to act.

Satellite SST also helps trigger targeted in-water observations. During the 2020 bleaching event, satellite data and in-water stations showed sustained marine heatwave conditions on the GBR. AIMS oceanographers, working with the IMOS Event Based Sampling program, deployed two autonomous gliders into the central and southern GBR to measure temperature through the water column in near real time. The gliders identified cooler water at depth in some reef passages, indicating potential thermal refugia. This information was communicated directly to reef managers and government agencies. Since 2018, satellite-triggered glider deployment has become a standing operational response, with an advisory committee reviewing SST observations and seasonal forecasts every one to two months and deploying gliders when risk thresholds are crossed.

While coral bleaching risk remains an important use case, AusTemp has a broader remit, supporting marine sectors across Australia to manage impacts of marine heatwaves. By incorporating both marine heatwave and marine cold spell categories, it directly supports fisheries, aquaculture, conservation, and ecosystem managers working beyond coral reef systems. In doing so, AusTemp helps translate ocean temperature data into decisions that protect livelihoods, ecosystems, and marine resources.