Quantcast

Bleaching Has Struck the Southernmost Coral Reef in the World

Oceans
Lord Howe Island lagoon in New South Wales, Australia. Peter Unger / Lonely Planet Images / Getty Images

By Tess Moriarty, Bill Leggat, C. Mark Eakin, Rosie Steinberg, Scott Heron and Tracy Ainsworth

This month corals in Lord Howe Island Marine Park began showing signs of bleaching. The 145,000 hectare marine park contains the most southerly coral reef in the world, in 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 investigate and document the bleaching.

Sustained heat stress has seen 90 percent of some reefs bleached, although other parts of the marine park have escaped largely unscathed.

Bleaching is Uneven

Coral bleaching observed at Lord Howe in March 2019.


Author Provided

Lord Howe Island was named a UNESCO World Heritage site in 1982. It is the coral reef closest to a pole, and contains many species found nowhere else in the world.

Two of us (Tess Moriarty and Rosie Steinberg) have surveyed reefs across Lord Howe Island Marine Park to determine the extent of bleaching in the populations of hard coral, soft coral and anemones. This research found severe bleaching on the inshore lagoon reefs, where up to 95 percent of corals are showing signs of extensive bleaching.

However, bleaching is highly variable across Lord Howe Island. Some areas within the Lord Howe Island lagoon coral reef are not showing signs of bleaching and have remained healthy and vibrant throughout the summer. There are also corals on the outer reef and at deeper reef sites that have remained healthy, with minimal or no bleaching.

One surveyed reef location in Lord Howe Island Marine Park is severely impacted, with more than 90 percent of corals bleached; at the next most affected reef site roughly 50 percent of corals are bleached, and the remaining sites are less than 30 percent bleached. At least three sites have less than 5 percent bleached corals.

Healthy coral photographed at Lord Howe marine park in March 2019.


Author Provided

Over the past week heat stress has continued in this area, and return visits to these sites revealed that the coral condition has worsened. There is evidence that some corals are now dying on the most severely affected reefs.

Forecasts for the coming week indicate that water temperatures are likely to cool below 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 event to the reef system, and investigate coral recovery.

What’s Causing the Bleaching?

The bleaching was caused by high seawater temperature from a persistent summer marine heatwave off southeastern Australia. Temperature in January was a full degree Celsius warmer than usual, and from the end of January to mid-February temperatures remained above the local bleaching threshold.

Sustained heat stressed the Lord Howe Island reefs, and put them at risk. They had a temporary reprieve with cooler temperatures in late February, but by March another increase put the ocean temperature well above safe levels. This is now the third recorded bleaching event to have occurred on this remote reef system.

Satellite monitoring of sea-surface temperature (SST) revealed three periods in excess of the Bleaching Threshold during which heat stress accumulated (measured as Degree Heating Weeks, DHW). Since January 2019, SST (purple) exceeded expected monthly average values (blue +) by as much as 2°C. The grey line and envelope indicate the predicted range of SST in the near future.


NOAA Coral Reef Watch

However, this heatwave has not equally affected the whole reef system. In parts of the lagoon areas the water can be cooler, due to factors like ocean currents and fresh groundwater intrusion, protecting some areas from bleaching. Some coral varieties are also more heat-resistant, and a particular reef that has been exposed to high temperatures in the past may better cope with the current conditions. For a complex variety of reasons, the bleaching is unevenly affecting the whole marine park.

Coral bleaching is the greatest threat to the sustainability of coral reefs worldwide and is now clearly one of the greatest challenges we face in responding to the impact of global climate change. UNESCO World Heritage regions, such as the Lord Howe Island Group, require urgent action to address the cause and impact of a changing climate, coupled with continued management to ensure these systems remain intact for future generations.

The authors thank ProDive Lord Howe Island and Lord Howe Island Environmental Tours for assistance during fieldwork.

Reposted with permission from our media associate The Conversation.

EcoWatch Daily Newsletter

"Globally, we're starting to see examples of retailers moving away from plastics and throwaway packaging, but not at the urgency and scale needed to address this crisis." Greenpeace

By Jake Johnson

A Greenpeace report released Tuesday uses a hypothetical "Smart Supermarket" that has done away with environmentally damaging single-use plastics to outline a possible future in which the world's oceans and communities are free of bags, bottles, packaging and other harmful plastic pollutants.

Read More Show Less
Children are forced to wear masks due to the toxic smoke from peat land fires in Indonesia. Aulia Erlangga / CIFOR

By Irene Banos Ruiz

Pediatricians in New Delhi, India, say children's lungs are no longer pink, but black.

Our warming planet is already impacting the health of the world's children and will shape the future of an entire generation if we fail to limit global warming to well below 2 degrees Celsius (35.6°F), the 2019 Lancet Countdown Report on health and climate change shows.

Read More Show Less
Sponsored
Private homes surround a 20 inch gas liquids pipeline which is part of the Mariner East II project on Oct. 5, 2017 in Marchwood, Penn. Robert Nickelsberg / Getty Images

The FBI is looking into how the state of Pennsylvania granted permits for a controversial natural gas pipeline as part of a corruption investigation, the AP reports.

Read More Show Less
Three cows who were washed off their North Carolina island by Hurricane Dorian have been found alive after swimming at least two miles. Carolina Wild Ones / Facebook

Three cows who were washed off their North Carolina island by Hurricane Dorian have been found alive after swimming at least two miles, The New York Times reported Wednesday.

Read More Show Less
The Dakota Access pipeline being built in Iowa. Carl Wycoff / CC BY 2.0

The fight between the Standing Rock Sioux and the owners of the Dakota Access Pipeline is back on, as the tribe opposes a pipeline expansion that it argues would increase the risk of an oil spill.

Read More Show Less
Sponsored
Scanning electron micrograph of Yersinia pestis, which causes bubonic plague, on proventricular spines of a Xenopsylla cheopis flea. NIAID / Flickr / CC BY 2.0

A middle-aged married couple in China was diagnosed with pneumonic plague, a highly infectious disease similar to bubonic plague, which ravaged Europe in the middle ages, as CNN reported.

Read More Show Less
Milk made from almonds, oats and coconut are among the healthiest alternatives to cow's milk. triocean / iStock / Getty Images Plus

Dairy aisles have exploded with milk and milk alternative options over the past few years, and choosing the healthiest milk isn't just about the fat content.

Whether you're looking beyond cow's milk for health reasons or dietary preferences or simply want to experiment with different options, you may wonder which type of milk is healthiest for you.

Read More Show Less
Greta Thunberg stands aboard the catamaran La Vagabonde as she sets sail to Europe in Hampton, Virginia, on Nov. 13. NICHOLAS KAMM / AFP via Getty Images

Greta Thunberg, the teenage climate activist whose weekly school strikes have spurred global demonstrations, has cut short her tour of the Americas and set sail for Europe to attend COP25 in Madrid next month, as The New York Times reported.

Read More Show Less