Keppel corals show resilience after intense bleaching

Corals in the southern Great Barrier Reef’s Keppel Islands survived and recovered from a severe bleaching event in 2020, indicating the high resilience of corals in the region, according to new research from the Australian Institute of Marine Science (AIMS).

Severe bleaching at Woppaburra Sea Country, near Yeppoon, was part of the 2020 Great Barrier Reef mass bleaching event and affected 75%-98% of coral on the islands.

But despite these corals being exposed to accumulated heat that often leads to mortality, coral cover in the area was found to have remained stable, with very little mortality.

AIMS scientist Dr. Kathy Page, said the recovery after the bleaching event was due to a reduction in heat stress in the area, possibly aided by environmental factors typical of the area, such as increased turbidity and high tidal flows.

However, he warned that corals may not fare as well in future events under a warming climate because cooler recovery periods are reduced, negating the benefits of high turbidity and water flow.

“The reefs in this area are considered ‘highly disturbed’ and have been affected by six major floods, four cyclones, four major storms and six coral bleaching events caused by marine heat waves over the past 30 years,” said Dr. “They’ve been through a lot and we wanted to know more about what makes them so tough.

“Our research shows a strong recovery after the 2020 event.

“The Keppel area is characterized by a large tidal range and strong currents which can help reduce water temperature, provide protection from the sun and provide additional food. Coastal corals are able to feed on organic matter resuspended from these currents and which provide nutrition in the absence of coral algal symbionts, which are lost in bleaching events.”

For the study, the team examined six reefs in different areas of the Keppel Island region in early April 2020 during the heat wave that caused severe bleaching. They surveyed these reefs, and three other sites, again in June and October 2020 to document the recovery of different species.

Dr Page said the Keppel reefs are dominated by fast-growing species of the Acropora family, which are very sensitive to bleaching, but which they found mostly survived the event.

“It may be that the frequent upheavals over 30 years have helped them to adapt to some extent,” he added. “But it is unknown how long these and resilient corals in other areas can maintain their ability to recover from bleaching events if they increase in frequency and intensity in a warming world.

“Frequent and severe bleaching events, such as the 2020 event we studied, highlight the importance of actions that slow and limit climate change.

“The study also shows the importance of studying coral recovery after bleaching events and other disturbances to better understand the complex dynamics at play in different regions of the Great Barrier Reef. This will help us predict how different reefs will react.” ”

Dr Page added that knowledge gained from the Keppels study may allow scientists to identify reefs in different areas that may be particularly resilient to future bleaching events. They could serve as a natural source of coral larvae to seed other reefs in an area. Coral seeding is a promising approach to help accelerate reef recovery on the Great Barrier Reef and around the world.

The research was published in the journal Ecosphere.