Back-to-back bleaching has now hit two-thirds of the Great Barrier Reef


Terry Hughes, James Cook University and James Kerry, James Cook University

Corals on the Great Barrier Reef have bleached again in 2017 as a result of extreme summer temperatures. It’s the fourth such event and the second in as many years, following earlier mass bleachings in 1998, 2002 and 2016. The Conversation

The consecutive bleaching in 2016 and 2017 is concerning for two reasons. First, the 12-month gap between the two events is far too short for any meaningful recovery on reefs that were affected in 2016.

Second, last year’s bleaching was most severe in the northern section of the reef, from the Torres Strait to Port Douglas, whereas this year the most intense bleaching has occurred further south, between Cooktown and Townsville. The combined footprint of this unprecedented back-to-back bleaching now stretches along two-thirds of the length of the Great Barrier Reef.

Last year, after the peak temperatures in March, 67% of the corals died along a 700km northern section of the reef – the single greatest loss of corals ever recorded on the reef.

Further offshore and to the south, most of the bleached corals regained their colour after the 2016 bleaching, and survived. The patchiness of the bleaching means that there are still sections of the Great Barrier Reef that remain in good condition.

It is still too early to tell how many corals will survive or die over the next few months in the central section as a result of this year’s bleaching.

Four major events

Each of the four bleaching events has a distinctive geographic pattern that can be explained by where the water was hottest for sustained periods during each summer.

For example, the southern Great Barrier Reef escaped bleaching in both 2016 and 2017 because the summer sea temperatures there remained close to normal. Similarly, the earlier mass bleaching events in 1998 and 2002 were relatively moderate, because the elevated water temperatures experienced then were lower than those in 2017 and especially 2016.

The marine heatwaves in 1998 and 2016 coincided with El Niño periods, but this was not the case in 2002 or this year, when water temperatures were also abnormally high. Increasingly around the tropics, we are seeing more and more bleaching events, regardless of the timing relative to the El Niño-La Niña cycle. This reflects the growing impact of global warming on these events.

The local weather also plays an important role in determining where and when bleaching occurs. For example, in 2016, ex-Tropical Cyclone Winston came from Fiji to Australia at the end of February as a rain depression, and cooled the southern region of the Great Barrier Reef, saving it from bleaching.

This year, the category 4 Tropical Cyclone Debbie tracked across the reef in late March, close to the southern boundary of the latest bleaching.

But TC Debbie was too far south to prevent the bleaching that was already under way in the reef’s central and northern sections. Instead of helping to ameliorate the bleaching, this powerful cyclone has added to the pressures on some southern reefs by smashing corals and exacerbating coastal runoff.

Prospects for the future

The fallout from this and last year’s events will continue to unfold in the coming months and years. It takes several months for severely bleached corals to regain their colour, or to die. On some reefs in the Great Barrier Reef’s central region, underwater surveys in 2017 are already documenting substantial loss of corals.

The recovery times for northern and now central reefs that have lost many corals will be at least 10-15 years, assuming that conditions remain favourable for corals during that period.

We have a narrowing window of opportunity to tackle global warming, and no time to lose in moving to zero net carbon emissions. We have already seen four major bleaching events on the Great Barrier Reef with just 1℃ of global average warming.

The goals enshrined in the Paris climate agreement, which aims to hold global warming well below 2℃ and as close as possible to 1.5℃, will not be sufficient to restore the Great Barrier Reef to its former glory. But they should at least ensure that we continue to have a functioning coral reef system.

In contrast, if the world continues its business-as-usual greenhouse emissions for several more decades, it will almost certainly spell the end of the Great Barrier Reef as we now know it.

Terry Hughes, Distinguished Professor, James Cook University, James Cook University and James Kerry, Senior Research Officer, ARC Centre of Excellence for Coral Reef Studies, James Cook University

This article was originally published on The Conversation. Read the original article.

Feeling helpless about the Great Barrier Reef? Here’s one way you can help


Justin Marshall, The University of Queensland; Chris Roelfsema, The University of Queensland, and Diana Kleine, The University of Queensland

It is easy to feel overwhelmed when confronted with reports of the second mass bleaching event on the Great Barrier Reef in as many years. But there is a way to help scientists monitor the reef’s condition. The Conversation

CoralWatch is a citizen science program started at The University of Queensland 15 years ago, with two main aims: to monitor the environment on a vast scale, and to help people get informed about marine science.

These goals come together with coral health monitoring. Divers, snorkelers or people walking around reef areas during low tides can send us crucial information about coral bleaching, helping us to build detailed pictures of the health of different reefs.

Participants can use a colour chart, backed up through the CoralWatch app or website, to measure accurately the colour and type of coral they see. The chart covers 75% of known corals, and can be used with no prior training.

We also ask people to enter the type of coral (branching, boulder, plate or soft), the location, and the weather. This allows scientists to identify the location and extent of any problems quickly (and is an excellent way to learn more about our reefs).

In fact, you don’t even have to go to a reef to participate and discover through CoralWatch; we have classroom and virtual reef systems, and just talking the problem through can help.

CoralWatch chart. Volunteers match the colour and four basic coral types: branching, boulder, plate and soft.
CoralWatch

The graphs shown below are samples of CoralWatch data from the northern and southern reef during 2016’s catastrophic mass bleaching event, while the pair of graphs further down the page show data from just a few days ago at Lady Elliot Island and the very remote North Mariana Islands in the West pacific.

The Heron Island graph shows a healthy reef, as the southern areas of the reef escaped the worst of the bleaching last year. In contrast, Monsoon Reef (which lies off Port Douglas) and many others in the north bleached badly, or in some cases simply died.

Scores averaging between four and six are normal and represent good levels of symbiotic algae, which generate nutrients for the coral. Scores below three signify that coral is in distress.

The impact of this year’s mass bleaching is still being quantified. However, reefs in the middle section and far south of the reef – such as Lady Elliot Island – are now showing varying degrees of bleaching, from light to severe. Many of the remaining corals in the north are also showing signs of bleaching again.

What seems certain is that we will lose many more corals, along with the fish and invertebrate life they support, again this year.

The results for the North Mariana Islands, from a CoralWatch survey conducted last week, shows mid-level coral bleaching and demonstrates that even very remote reefs are not climate-proof.

Australians increasingly believe the government needs to act on climate change, and some of this change in opinion is likely fuelled by continued reports of coral bleaching.

CoralWatch doesn’t only help build a detailed picture of reef health. Like other citizen science projects, such as Reef Check, it can help speed up our fatally slow response to climate change. There are three key benefits.

First, we need to improve mutual understanding between scientists and the public. The CoralWatch mantra is: tell me and I’ll forget; teach me and I may remember; involve me and I’ll learn. Citizen science is a natural fit for everyone, no matter your level of education or knowledge.

Children are the citizens of the future, and helping them to understand their changing world is a moral and social imperative. CoralWatch works closely with schools and groups like the Marine Teachers Association of Queensland, and is used in more than 75 countries worldwide.

Second, we need to encourage lifestyle change. Many people, as they become more engaged in citizen science, will naturally adopt more environmentally friendly habits. Getting involved in protecting the Great Barrier Reef – and other citizen science projects – can be a great dose of perspective on our place in the natural world.

However, as personally rewarding as they can be, individual lifestyle choices alone won’t deliver the rapid and widespread change we need to save our reefs. That’s why we need to bridge the disconnect between what most of Australia wants and the politicians who ultimately have the power to fast-track change. Citizen scientists are also informed voters and consumers, who can demand better policies from companies and governments.

The future of the Great Barrier Reef is in the hands of Australians, and it will take all of us to preserve it for our children.

Justin Marshall, ARC Laureate Fellow, The University of Queensland; Chris Roelfsema, Research Fellow (Coastal and Marine), The University of Queensland, and Diana Kleine, Coral Watch Project Manager, The University of Queensland

This article was originally published on The Conversation. Read the original article.