The Great Barrier Reef, one of the world’s most iconic natural wonders, has been facing unprecedented threats due to climate change. Rising sea levels, more frequent heatwaves, and extensive bleaching have pushed the reef to the brink of collapse. However, a new study led by Professor Jody Webster from the University of Sydney suggests that the reef may be more resilient than previously thought.

The research, published in Nature Communications, draws on a geological time capsule of fossil reef cores extracted from the seabed under the Great Barrier Reef. The findings indicate that rapid sea level rise alone did not spell the end of the reef’s predecessor, Reef 4. Instead, it was the combination of environmental stressors such as poor water quality and warming climates that led to its demise about 10,000 years ago.

The study reveals that Reef 4, also known as the proto-Great Barrier Reef, had a similar morphology and mix of coral reef communities to the modern Great Barrier Reef. The types of algae and corals, and their growth rates, are comparable. Understanding the environmental changes that influenced it and led to its ultimate demise offers clues on what might happen to the modern reef.

Professor Webster and his colleagues used radiometric dating and reef habitat information to accurately pinpoint core samples pertaining to Meltwater pulse 1B, a period when global sea levels rose very rapidly. The cores underpinning this research were obtained under the International Ocean Discovery Program (IODP), an international marine research collaboration involving 21 nations.

The findings lend weight to already grave concerns about the Great Barrier Reef’s future. If the current trajectory continues, we should be concerned about whether the reef will survive the next 50 to 100 years in its current state. However, the study suggests that a healthy, active barrier reef can grow well in response to quite fast sea level rises.

The importance of learning from the past and understanding how reef and coastal ecosystems have responded to rapid environmental changes cannot be overstated. These data allow us to more precisely understand how reef and coastal ecosystems have responded to rapid environmental changes, like the rises in sea level and temperature we face today.

As we move forward with climate change mitigation efforts, it is crucial that we take a holistic approach, considering not only the direct impacts of rising sea levels but also the associated environmental stressors. By doing so, we may be able to prevent or slow down the decline of the Great Barrier Reef and ensure its continued resilience for generations to come.

A groundbreaking study published in the journal Coral Reefs has revealed that heat-tolerant symbiotic algae may hold the key to saving Florida’s elkhorn coral (Acropora palmata), a foundational species in Caribbean reef ecosystems, from the devastating impacts of marine heatwaves and coral bleaching.

The research, conducted by scientists at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science, in collaboration with other institutions, provides timely insights into the thermal tolerance of elkhorn coral. The study tested 172 elkhorn coral colonies sourced from restoration nurseries stretching from Miami to the lower Florida Keys, using custom-built rapid heat stress testing systems onboard a research vessel.

The findings showed that elkhorn corals hosting the heat-tolerant symbiont Durusdinium could survive short-term exposure to temperatures almost 2°C higher than those with the more common Symbiodinium. These resilient colonies were sexually derived juvenile corals that had acquired Durusdinium in a land-based facility, providing evidence that manipulating symbiont communities in early life stages can be an effective strategy for producing heat-tolerant corals for restoration.

“This study represents the most extensive thermal tolerance dataset gathered on A. palmata,” said Richard Karp, lead author of the study. “By incorporating novel interventions like heat-tolerant symbionts into restoration efforts, we can boost coral resilience and help restore this iconic species.”

The findings come at a critical time, as a global coral bleaching event has already impacted 84 percent of the world’s reefs. The study emphasizes the importance of scaling up symbiont-based interventions as part of current and future coral conservation and restoration work.

“This is an example of Florida’s reef scientists sharing their scientific and restoration expertise to make critical discoveries,” said Andrew Baker, a professor at the Rosenstiel School. “We need to continue to innovate and think outside the box to help coral reefs in their fight for survival against continued warming and coral bleaching.”

The health of our planet’s coral reefs is facing a double threat: disease and poor water quality. In recent years, coral diseases have caused significant declines in coral populations, especially affecting staghorn (Acropora cervicornis) and Elkhorn (A. palmata) corals that play a crucial role in reef ecosystems.

Despite efforts to identify the pathogens responsible for diseases like White Band Disease (WBD) and Stony Coral Tissue Loss Disease (SCTLD), the specific agents remain largely unknown. This lack of knowledge makes it challenging to develop effective strategies for coral restoration programs, which aim to restore these once-abundant coral species.

A recent study conducted by scientists at the University of Miami NOAA Cooperative Institute for Marine and Atmospheric Studies (CIMAS) and the Atlantic Oceanographic and Meteorological Laboratory (AOML) has shed light on how different coral genotypes respond to environmental stressors. The researchers examined 10 genotypes commonly used in coral restoration in South Florida, exposing them to two nutrient conditions: normal (ambient) or high ammonium levels.

The study’s key findings include:

• Coral genotypes that previously showed disease resistance did not necessarily maintain that resistance in this experiment, suggesting disease susceptibility may change based on disease cause, environment, or route of infection.
• Elevated dissolved inorganic nitrogen, in the form of ammonium, reduced coral survival – even in the absence of disease – highlighting poor water quality as a significant threat.
• When exposed to disease under normal conditions, four genotypes suffered complete mortality, while others showed varying degrees of resilience.
• When both stressors were combined, all genotypes experienced mortality rates ranging from 30 to 100 percent.

The researchers emphasize the urgent need for improving water quality by limiting runoff to support coral conservation efforts. Since coral disease outbreaks often coincide with pollution-related stress, reducing nutrient pollution is critical to enhancing coral resilience and increasing the success of restoration projects.

“If water quality issues are not addressed, it will be difficult for both wild and restored coral colonies in Florida to survive,” said Ana Palacio, the lead author of the study and a research scientist at CIMAS. “Our findings highlight the importance of selecting coral genotypes that are resilient to local stressors and ensuring improved water conditions before restoration efforts.”

Coral reefs provide essential ecosystem services, including coastal protection, marine biodiversity, and economic benefits to fisheries and tourism. This study underscores the importance of science-driven policymaking and conservation strategies to safeguard these vital ecosystems for the future.

Funding for the study was provided to Ana M Palacio-Castro through the National Academy of Sciences’ National Research Council (NRC) Postdoctoral Fellowship and the Coral Reef Conservation Program (Grant 31250).