The future remains bleak for corals – but not all reefs are doomed

 

Christopher Cornwall, CC BY-NC-ND

Christopher Cornwall, Te Herenga Waka — Victoria University of Wellington and Orlando Timmerman, University of Cambridge

A recent report on global tipping points warned that coral reefs face widespread dieback and have reached a point from which they cannot recover.

But in our new research, we show this might not be the case for some reefs if corals can gain tolerance to rising temperatures, or if we can cut greenhouse gas emissions and restore reefs with heat-tolerant corals at scale.

Nevertheless, the outlook likely remains bleak.

 

All coral reefs are under threat but some may be more tolerant to warming waters. Christopher Cornwall, CC BY-NC-ND

Coral reefs provide habitat for thousands of other species in tropical oceans. They deliver economic value through fisheries and tourism and provide shoreline protection from storm surges and extreme weather by dampening the impact of waves.

However, coral reefs are vulnerable to the effects of climate change. Our study combines previously published assessments of climate impacts on different coral reefs and reviews the scientific consensus to examine how long reef structures could persist as climate change intensifies.

Ocean warming, acidification, darkening and deoxygenation all threaten the persistence of coral reefs. Ocean warming brings marine heatwaves, which are the leading cause of mass coral bleaching that has led to a global decline in coral cover.

Marine heatwaves have already led to a global decline in coral reefs. Christopher Cornwall, CC BY-NC-ND

Corals are animals that house microalgae within their tissues that provide sugar in exchange for nitrogen. When temperatures become too hot, corals expel these symbiotic microalgae, leaving behind white skeletons.

Ocean acidification reduces the ability of corals to build their skeletons through a process called calcification. Warming, darkening and deoxygenation can also reduce calcification.

When corals expel their symbiotic algae, all that remains are bleached skeletons. Chris Perry, CC BY-NC-ND

Coral reefs are built by adding calcium carbonate, coming mostly from corals but also coralline algae and other calcareous seaweeds. But as the ocean’s pH (a measure of acidity) is reduced, processes called bio-erosion and dissolution act to remove calcium carbonate.

Our meta-analysis examined how climate change affects the calcification and bio-erosion of coral reefs and we then applied these results to a global data set of reef growth.

There is no scientific consensus on which organisms will build future coral reefs. We explore four most likely scenarios:

1. Present-day extreme reefs represent the future of coral reefs. These are locations where temperatures are already warmer, waters are becoming more acidic and oxygen has dropped to conditions similar to those expected at the end of the century. These reefs are dominated by coralline algae and slow-growing heat-resistant corals.

Some reefs already experience conditions expected at the end of the century. Steeve Comeau, CC BY-NC-ND

2. Presently degraded reefs take over future reefs. These reefs are dominated by bio-eroders such as sponges and sea urchins and have low coral cover.

3. Corals can gain heat tolerance to an extent that keeps pace with low to moderate greenhouse gas emissions scenarios. Under these scenarios, only about 36% of global corals would be lost and there would be a moderate reduction in growth. These heat-tolerant reefs are dominated by faster growing corals with symbiotic microalgae that can evolve heat tolerance.

4. Reefs where restoration practices include using heat-tolerant corals that can then disperse to other regions. These restored reefs would have lower coral cover in remote regions lacking restoration or with unsuccessful restoration practices. This kind of reef restoration would need to cover half of global coral reefs to maintain net growth – an unlikely scenario.

We found coral reefs transition to net erosion under all scenarios, even under low to moderate greenhouse gas emissions, meaning they are dissolving or being eaten faster than they can grow. Only reefs with heat-tolerant corals could prevent this from occurring.

The next step for the scientific community is to determine which reefs can persist in the future using global efforts to combine information. The major issues is that we are missing measurements from large parts of the Pacific, and we do not know how deoxygenation or coastal darkening will impact coral reefs. The processes of reef bioerosion and dissolution are also poorly described.

Although the climate has been altered to the point of threatening the future survival of coral reefs, their fate is not doomed yet if we act now.

Another question is how long reef structures will persist after living corals are removed. We do not have an answer yet. It will take global efforts to rapidly obtain these measurements to better manage and protect coral reefs before climate change intensifies.

It is up to governments everywhere, including New Zealand, to better support these initiatives before it is too late.

Christopher Cornwall, Lecturer in Marine Biology, Te Herenga Waka — Victoria University of Wellington and Orlando Timmerman, Doctoral Candidate in Earth Sciences, University of Cambridge

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→March 16, 2026

Microbes in Antarctica survive the freezing and dark winter by living on air

Ry Holland, Monash University

Winter in Antarctica is long and dark. Temperatures remain well below freezing. In many places, the Sun sets in April and does not rise above the horizon again until August. Without sunlight, photosynthetic life such as plants, mosses and algae cannot make energy.

But that’s not to say all life stops.

In a new study published in The ISME Journal, my colleagues and I show that Antarctic microbes make energy from the air at temperatures as low as –20°C. This finding improves our understanding of how life survives at temperature extremes in Antarctica – and how climate change will affect this important process.

How to make energy from air

In 2017, scientists showed that a large number of Antarctic microbes can generate energy from atmospheric gases present at very low concentrations.

This process is called “aerotrophy”. By using enzymes that are very finely tuned to “sniff out” the hydrogen and carbon monoxide in the atmosphere, these microbes have found a way to make energy from the air itself – a huge advantage in Antarctica’s nutrient-poor desert soils.

What remained unknown until now was the temperature limits of this process. Could aerotrophy be a way to power the continent’s soil communities through the winter?

Taking the lab down south

Measuring how quickly these microbes consume such a small amount of fuel can be difficult.

From 2022–24, we collected surface soil samples from different areas across East Antarctica and analysed them in our lab.

We measured how quickly they can use the atmospheric gases. We also extracted all the DNA from the soil microbes and sequenced it. This tells us what microbes are present, what genes they have, and what they are capable of using as energy sources.

We showed aerotrophy happening in the lab at representative summer (4°C) and winter (–20°C) temperatures. This means hydrogen and carbon monoxide are a viable food source not just over the summer months, but year-round. What was even more surprising though, was the upper temperature limit.

Soil temperatures in Antarctica rarely rise above 20°C. Yet we found microbes in these soils that continued to generate energy from hydrogen up to a staggering 75°C. It seems as though microbes in Antarctic soils are well adapted to the continent’s cold temperatures, but not restricted to them. It’s a bit like seeing a penguin thrive in a tropical jungle.

We also wanted to see this process occurring in Antarctica itself, so two years ago we brought the lab down south. We collected fresh soil samples, sealed them in the glass vials, and took gas samples.

For the first time, it was clear that under real-world conditions these soil microbes were still munching their way through hydrogen.

The primary producers of Antarctica

DNA sequencing has showed us that the vast majority of microbes in Antarctic soils encode the genes to gain energy from hydrogen. Many of these bacteria also have genes to take carbon from the atmosphere.

These aerotrophs are “primary producers”, generating new biomass from the air itself.

In most land-based ecosystems, photosynthesis is thought to be the bottom of the food chain. Photosynthesis takes energy from sunlight and carbon from the atmosphere and turns it into yummy organic compounds.

It’s what makes plants grow. Plants are primary producers that are eaten by herbivores, which are then eaten by carnivores.

In Antarctica’s desert soils, photosynthesis is relatively rare. Instead, we hypothesise that aerotrophy fulfils the primary producer role in many places.

This makes sense because, unlike sunlight-dependent photosythesis, we now know that aerotrophy can happen year-round. Another benefit is that it doesn’t require liquid water, whereas photosynthesis does.

Hydrogen in a heating world

Aerotrophy clearly has an important role in Antarctic ecosystems. So next, we wanted to determine how global warming might affect this process.

Under low-emissions scenarios, we predict a 4% increase in how quickly aerotrophs use atmospheric hydrogen. Under very high-emissions scenarios, this increase rises to 35%. The numbers are similar for carbon monoxide.

Although hydrogen isn’t a greenhouse gas itself, it is important because it affects how long some greenhouse gases, including methane, hang around in the atmosphere.

Soils (including the microbes that live in them) are responsible for 82% of all hydrogen consumed on Earth globally. In other words, they are a hydrogen sink. This is a crucial component in the global hydrogen cycle.

There are a lot of factors that determine how microorganisms will respond to climate change. Temperature is just one of them. This study is an important piece of the puzzle as scientists figure out how resilient Antarctica’s unique microbal ecosystems are.

Ry Holland, Research Fellow in Microbial Ecology, Monash University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→March 12, 2026