A new paper by the NOAA Coral Reef Watch (CRW) program, an initiative supported by the ESSIC-administered Cooperative Institute for Satellite Earth System Studies (CISESS), shows that Australia’s Great Barrier Reef (GBR) started the 2021-2022 summer season with more accumulated oceanic heat stress than ever before in the satellite record (i.e., 1985 to the present). As of December 14, 2021, NOAA CRW’s daily global 5km satellite coral bleaching heat stress products indicated that instantaneous heat stress and accumulated heat stress over the prior 12 weeks were unprecedented on the GBR.
Led by ESSIC/CISESS subawardee Blake Spady, and including fellow subawardee, William Skirving, and ESSIC/CISESS scientists, Gang Liu and Jacqueline De La Cour, the study shows that for 87% of the 5km-resolution satellite coral reef pixels on the GBR, the minimum sea surface temperature between November 16 and December 14, 2021 was greater than the maximum temperature ever experienced at those locations within that same 29-day period from 1985-2020.
Ongoing La Niña conditions typically generate high cloud cover, precipitation, and an increased potential for tropical storms/cyclones over the GBR, all of which could provide the reef with some relief from heat stress. However, even with two tropical cyclones that have already passed through the GBR this summer, cooling some areas dramatically, CRW’s modeled Four-Month Coral Bleaching Outlook still forecasts additional heat stress throughout February and March for the region.
Additionally, CRW’s daily global 5km satellite Bleaching Alert Area (7-day maximum) product currently places the full extent of the northern GBR at a minimum of Coral Bleaching Alert Level 1 (capable of causing significant coral bleaching), with significant portions at Bleaching Alert Level 2 (capable of causing severe, widespread bleaching and significant mortality).
If the current heat stress results in significant bleaching, which is expected, this will be the first known mass coral bleaching event on the GBR during a La Niña.
A severe marine heatwave and bleaching event would significantly impact ongoing recovery of GBR corals, which sustained major bleaching and damage during the widespread mass bleaching events of 2016, 2017, and 2020. This could have disastrous consequences for one of the most biodiverse and valuable ecosystems on Earth.
“NOAA Coral Reef Watch staff are continuing to monitor closely our modeled Four-Month Coral Bleaching Outlook and our daily global 5km satellite products, to assess the developing heat stress on the GBR, and elsewhere around the world,” commented De La Cour, “This allows us to quickly and effectively communicate changes in the coral reef environment, that can impact local reefs, to our extensive network of partners and users worldwide.”
More than 1 billion people rely on coral reefs for food, coastal protection, their livelihoods, and even their cultural identity. Coral reef ecosystems support subsistence, recreational, and commercial fisheries, tourism, and shoreline protection, and they yield compounds important for medicinal development. Using CRW’s products, resource managers, researchers, and the public can better understand links between environmental conditions and ecosystem impacts; assess when reefs are vulnerable or resilient to climate change and its impacts (especially coral bleaching and disease); and prepare and prioritize resources to implement timely, effective protective responses and adaptation actions in the water. Some protective measures users have implemented in response to CRW’s modeled and satellite-based products have included reducing local stressors during high oceanic heat stress (e.g., by closing major scuba diving and fishing areas), rescuing rare corals, and shading/cooling key nursery reefs.
Future studies will need to investigate the oceanic and climatic patterns contributing to the exceptionally warm early-summer conditions on the GBR for late 2021.
Click here to follow CRW’s modeled Four-Month Coral Bleaching Outlook, and here to access the daily global 5km satellite products, to monitor the developing heat stress on the GBR and elsewhere around the world.