See more of the story

Following dire warnings of reef die-off after massive coral bleaching in 2016 and 2017, Tourism and Events Queensland has issued a “positive update” on the status of Australia’s Great Barrier Reef, reporting that some affected areas are showing “substantial signs of recovery.”

The nonprofit Reef & Rainforest Research Centre (RRRC) has reported signs of recovery due to a milder 2017-18 summer, as well as cooperation among science, industry and government in supporting the reef’s recovery, according to the report issued on Wednesday by the Queensland State ­Government.

Stretching more than 1,430 miles along Queensland’s spectacular coastline, the Great Barrier Reef is the longest coral reef in the world and the first coral reef ecosystem to be awarded UNESCO World Heritage Status.

Coral bleaching occurs when coral experiences stress from heightened water temperatures or poor water quality. In response, the coral ejects a photosynthetic algae called zooxanthellae, which removes the coral’s distinctive color. If the stress conditions persist, the coral will die, the report says, but if conditions return to acceptable levels, some coral can reabsorb the substance and recover.

The RRRC, in cooperation with the Association of Marine Park Tourism Operators, conducted detailed surveys at key tourism dive sites around the city of Cairns in 2016 and 2017 and said certain reefs that were strongly affected in the bleaching event are showing significant signs of improvement.

Coral bleaching occurs in multiple stages, according to RRRC Managing Director Sheriden Morris, ranging from the equivalent of a mild sunburn to coral mortality.

“When a reef is reported as ‘bleached’ in the media, that often leaves out a critical detail on how severe that bleaching is, at what depth the bleaching has occurred and if it’s going to cause permanent damage to the coral at that site,” Morris said in the statement, adding that the Barrier Reef “has significant capacity to recover from health impacts like bleaching events.”

Still, he warned that the recovery is “contingent on environmental conditions” and that the reef “may suffer further bleaching events as the climate continues to warm.”

The full impact of the 2016 bleaching, which damaged or destroyed 30 percent of the reef’s shallow water coral, has not yet fully been assessed, according to a report released on Tuesday by the Nature Research Journal.

Deeper reefs are often considered a refuge from thermal anomalies such as those experienced in 2016 and 2017, but the report argues that both shallow and deep reefs are threatened by mass bleaching events; even when the upwelling of colder water (which replaces warmer water pushed offshore by winds) stopped at the end of summer, temperatures at depth rose to record-high levels. Researchers found bleached coral colonies as far down as 131 feet beneath the ocean’s surface, according to the report.