This month, corals at Ynys Howe Marine Park began to show signs of bleaching.
The 145,000 hectare marine park contains the most southerly coral reef in the world, one of the most isolated ecosystems on the planet.
Following early reports of bleaching in the area, researchers from three Australian universities and two government agencies have worked together throughout March to research and document the bleaching.
Continued heat stress has resulted in 90 per cent of some reefs being bleached, although other parts of the marine park have escaped unharmed.
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Singing is uneven
Lord Howe Island was named UNESCO World Heritage site in 1982. The coral reef is closest to a pole, and includes many unseen species anywhere in the world.
Two of us (Tess Moriarty and Rosie Steinberg) have carried out a survey of reefs across Lord Howe's Marine Park to determine the extent of bleaching in the populations of hard coral, soft coral and anemones.
This research found a serious bleaching of the lagoon reefs on the banks, where up to 95 per cent of corals show extensive bleaching signs.
However, bleaching is very variable across Lord Howe Island. Some areas within Lord Howe's lagoon coral reef do not show bleaching signs and have remained healthy and active throughout the summer. There are also corals on the outer reef and on deeper reef sites that have remained healthy, with little bleaching.
One reef site surveyed at Lord Howe Island Marine Park has been seriously affected, with more than 90 per cent of the corals bleached; In the next most affected reef site, about 50 percent of corals are bleached, and the remaining sites are less than 30 percent having bleached. At least three sites have less than 5 per cent of bleached corals.
Over the past week, heat stress has continued in this area, and visits to these sites revealed that the coral condition has deteriorated. There is evidence that some corals are now dying on the most affected reefs.
The forecast for next week shows that water temperatures are likely to cool under the bleaching threshold, which will hopefully provide timely relief for corals in this valuable reef ecosystem. In the coming days, weeks and months we will continue to monitor the affected reefs and determine the impact of this incident on the reef system, and investigate coral recovery.
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What causes the bleaching?
The bleaching was caused by high sea water temperatures from persistent maritime weather in the summer from south-east Australia. The temperature in January was Celsius warmer than usual, and from the end of January to mid-February the temperature remained higher than the local bleaching threshold.
He stressed the continued heat of Lord Howe's Island reefs, and put them at risk. They had a temporary reaction with cooler temperatures at the end of February, but by another March another increase in ocean temperature was well above safe levels. This is the third bleaching event now recorded on this remote reef system.
However, this hot weather system has not been affected by this hot weather. In parts of the lagoon areas the water may be cooler, due to factors such as ocean currents and fresh groundwater intrusion, protecting some areas from bleaching.
Some corals are also more heat-resistant, and a particular reef that has been exposed to high temperatures in the past can better cope with the current conditions. For a complex variety of reasons, the bleaching affects unevenly on the entire marine park.
Bleaching coral is the biggest threat to the sustainability of coral reefs worldwide and is now clearly one of the biggest challenges facing us in responding to the impact of global climate change.
UNESCO World Heritage regions, such as the Lord Howe Island Group, are asking for urgent action to tackle the cause and effect of a changing climate, along with ongoing management to ensure that these systems are in place. remain intact for future generations.
The authors thank ProDive Lord Howe Island and Lord Environmental Island Tours for help during fieldwork.
By Tess Moriarty, Phd candidate, Newcastle University; Bill Leggat, Associate Professor, Newcastle University; C. Mark Eakin, Co-ordinator, Coral Reef Protection, National and Atmospheric Ocean Administration; Rosie Steinberg, PhD Student, UNSW; Scott Heron, Senior Lecturer, James Cook University, and Tracy Ainsworth, Associate Professor, UNSW
This article is being republished from The Conversation under a Creative Commons license. Read the original article.