It is a building of superlatives, the largest structure on our planet built by animals, even recognizable from space. More than 1500 fish and 4000 mollusc species are native here: on the Great Barrier Reef. Hundreds of species of soft and hard corals form a 2000 kilometer long reef complex off Australia’s east coast, almost as big as Germany; an ecosystem overflowing with life. Since 1981 it has been allowed to adorn itself with the title “Unesco World Natural Heritage”. Unesco speaks of “one of the most spectacular landscapes on earth”, of a place of “outstanding beauty”.
In fact, the natural wonder is now only a shadow of its former splendor in many places. The most recent analysis by the International Union for Conservation of Nature (IUCN) on the location of the world natural heritage classifies the condition of the Great Barrier Reef as critical and therefore worse than at the last inventory. The main cause of its precarious condition is climate change. Global CO₂ emissions are acidifying the oceans and water temperatures are rising. In particular, the warming of the ocean affects the builders of the reefs – calcareous hard corals. It leads to the collapse of the symbiosis with vital microalgae and makes the corals bleach.
Over the past 25 years, the Great Barrier Reef has lost half of its corals after several mass bleaches as a result of oceanic heat waves. Most recently, at the beginning of 2020, a severe bleaching occurred off the Australian east coast, which also affected the southernmost part of the reef, which had been spared until then. Partly responsible for the massive losses are environmental pollution, especially from agriculture, and voracious crown-of-thorns, which attack corals like grasshoppers.
Heat waves, storms and population declines hardly allow recovery on its own
Damaged reefs can in principle regenerate – fast-growing species within ten to 15 years. But heat waves at ever shorter intervals, a higher susceptibility to tropical cyclones and a decimated population of sexually mature corals hardly allow recovery on one’s own.
The Australian government, which, under the influence of the coal lobby, rejects an ambitious reduction in CO₂ emissions, wants to stop the complete collapse of the Great Barrier Reef with hundreds of millions of dollars. Substantial sums are to be used, among other things, to improve the water quality and contain the starfish population. In addition, one wants to reforest destroyed reef sections and at the same time make them fit for climate change. With partly unconventional measures.
Gluttonous starfish also attack the reef.
(Photo: KATHARINA FABRICIUS / AFP)
“We are in a race against time to find solutions that will help corals survive ocean warming,” said David Meads of the Australian Institute for Marine Sciences in Townsville, Queensland. He heads a national research program worth a good 90 million euros. In it, marine scientists try out new techniques for restoring large areas of coral reefs, protecting them from extreme temperatures and equipping reef builders for a warmer environment.
They collect sperm and egg cells from spawning corals in order to raise larvae in swimming kindergartens and then release them into the sea millions of times. They breed more robust species by crossing species with selected traits, and train corals and their single-cell algae lodgers in the laboratory to withstand heat stress and more acidic water. And they are developing fog machines to provide shade for the Great Barrier Reef.
The researchers ambush the corals during sex in order to fish out egg cells and sperm
The results of their work are not only intended to save the native corals, but also serve as a blueprint for the worldwide rebuilding of reefs that have literally been devastated by mass bleaching. The researchers are still at the beginning of testing some of the measures, while other projects are already showing their first successes.
Field tests on reef restoration by marine ecologist Peter Harrison are very promising. He conducts research at Southern Cross University and helped discover the annual mass spawning of corals in the early 1980s. Today he and his colleagues lie in wait for the corals during synchronized sex under cover of darkness in order to fish out their eggs and sperm. The goal: to increase the chances of survival of the coral larvae so that they secure the future of the reef.
Corals produce their offspring in the water by ejecting egg cells and sperm in a synchronized manner, as here on a reef in southern Taiwan.
(Photo: HANDOUT / REUTERS)
“The larvae are descendants of corals that have survived the last bleaching events,” explains the researcher. So you have the right genes and a certain amount of heat tolerance. For a week they develop in pools floating in the sea. Then they are released – still tiny – on damaged reefs. Hoping that some of them will start new colonies. A pilot test off the coral island of Heron Island is encouraging: Harrison’s larvae grew into plate-sized coral sticks in just a few years and should soon reproduce themselves.
However, Harrison says that it is not possible to restore all of the destroyed sections of the Great Barrier Reef. Therefore, one concentrates on reefs that supply others with coral offspring via the current. “The biggest challenge is to produce hundreds of millions of larvae and deploy them widely,” says Harrison.
As early as 2017, a team from the USA and Australia argued in the specialist magazine Nature Ecology and Evolutionthat traditional approaches such as the laborious reef restoration with coral seedlings will not stop the global reef death. Because even limiting global warming to 1.5 to two degrees – which the international community is currently far removed from – means that most corals will get too hot in the near future. Also because the pace of climate change is beyond their natural adaptability.
According to the authors, more radical measures are necessary for corals to populate the tropical seas beyond the 21st century. Science must help the cnidarians adapt to climate change and accelerate the spread of beneficial genes: evolution in time lapse.
Cemetery walk: a turtle swims over faded corals.
(Photo: STR / AFP)
This idea is pursued in the laboratories of the Australian Institute for Marine Sciences. There corals from the hot north are crossed with those living further south. The result is hybrids that can withstand both heat and cooler water temperatures and should make the central and southern Great Barrier Reef more resilient to ocean warming. If one relied solely on natural selection: it would take many generations before the genetically anchored heat tolerance of the northern corals reached other reef regions. But the natural wonder is running out of time.
In another project, corals and the symbiotic algae that nestle in their tissues grow under conditions that they can barely tolerate. They are supposed to harden at elevated temperatures and CO₂-rich, i.e. more acidic, seawater. If the training is reflected in the genome, the offspring would be less susceptible to coral bleaching or a porous calcareous skeleton.
At the same time, it is clear that such complex and costly methods are ideally suited to saving key species and reef sites of particularly high biological value. In addition, they could disrupt the finely balanced structure of coral reefs and create new problems, such as an increased susceptibility to disease.
Artificial clouds could buy the reef a little more time
“You have to weigh the risks of interfering with the complex ecosystem and doing nothing,” says David Meads. Without intervention, the worsening climate crisis threatens permanent loss of biodiversity and important reef functions: “A quarter of all marine life and a billion people depend on coral reefs as a source of food and income. They protect coastlines from storms and erosion and bring financial benefits to the local economy Benefit of US $ 30 billion worldwide. “
In any case, some research is needed before the measures can be deployed on a larger scale. The fate of the Great Barrier Reef depends above all on a massive decline in global CO₂ emissions. So far, however, this is not in sight.
Daniel Harrison from Southern Cross University therefore wants to buy the corals more time by lightening the clouds. The engineer is working on a method of transforming seawater into condensation nuclei for cloud droplets that reflect some of the solar radiation. Last year he tested a machine the size of a snow cannon off the Australian coast. This sprays seawater into the atmosphere, which quickly evaporates. Tiny salt crystals remain, which contribute to cloud growth. “With cloud lightening, you could cool the ocean surface for several weeks if a heat wave hits and coral bleaching threatens,” says Harrison. However, there are a number of unanswered questions. For example, how the enormous energy demand would be covered if the technology were to be used on a large scale and whether it would have an impact on precipitation over the ocean or on land.
Nevertheless, Harrison is optimistic: “I hope that the technology can help to preserve corals long enough. So that they have a chance to adapt to the new environmental conditions when humanity no longer emits greenhouse gases in an uncontrolled manner.”