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Coral can’t escape climate change

A new paper shows that despite coral’s natural adaptive capacity, even moderate global warming could see the destruction of our coral reefs.

Dr Christopher Cornwall from Te Herenga Waka—Victoria University of Wellington's Te Kura Mātauranga Koiora—School of Biological Sciences led the study, and says the results are concerning.

“We found that corals’ natural adaptive capacity would not be enough to save the reefs from eroding due to climate change. Not unless we stop emitting greenhouse gases immediately and start developing techniques to remove the gases from our atmosphere.”

Coral colonies are supported by a rigid skeleton of calcium carbonate, similar in structure to our bones, surrounded by soft ‘polyps’ that look like an anemone. Inside these polyps live tiny, microscopic algae that provide nutrition to the coral.

While coral has a very long generation time—years to decades—that limits their ability to evolve in response to stress, the algae have much shorter generation times that could allow rapid evolution. Some algae have higher thermal tolerance and corals could “shuffle” these, taking up more heat tolerant ones.

Coral adaptive capacity insufficient to halt global transition of coral reefs into net erosion under climate change, published in the journal Global Change Biology today, models how calcium carbonate production could change under climate change with and without the coral evolving tolerance to warming seawater.

The study looked at how production of calcium carbonate would be affected under three warming and acidification scenarios. The scenarios looked at warming between 2050 and 2100, Representative Concentration Pathways (RCP) 2.6, where warming is between 0.7°C and 0.98°C; RCP 4.5, between 0.87°C and 1.59°C; and RCP 8.5, between 1°C and 2.43°C.

Dr Cornwall says the results show that average coral reef growth globally across the sites he examined only stayed positive under RCP 2.6.

“Only 9 to 35% of our reefs would still be growing by 2050 in scenarios with coral evolution, depending on both greenhouse gas emissions, but in the Atlantic and Indian Oceans they would all be eroding.

“However, only 9 to 13% would still be growing by 2050 without evolution.”

He says the natural adaptive capacity of coral will only be able to ensure slightly increased growth rates under lower emissions scenarios.

“Under our worst-case scenarios, only 6 out of the 201 reefs we examined would survive.

“The results show that there’s an immediate need to reduce greenhouse gas emissions if we want our reefs around in the long term.”

Dr Cornwall says coral reefs are crucial parts of their ecosystems in tropical and sub-tropical regions, providing homes for nearly a quarter of marine life, and helping to protect our coastlines from erosion, creating a barrier between the ocean and the shore.

“We’ve seen a lot of damage already with mass coral bleaching events caused by marine heatwaves, but their ability to persist and continue growing is going to be strongly influenced by ongoing warming.

“Many corals just won’t be able to adapt quick enough, and we could lose almost or all of their ecological function across the globe.”

One solution that has been discussed widely, Dr Cornwall says, is to propagate more heat-tolerant species with high rates of calcium carbonate production in habitats most at risk.

“The challenge is that the species that are more heat-tolerant tend to be the ones that grow slower, and the ones that grow faster are the most heat sensitive.

“Really, the best solution is to keep warming below 1.5 degrees and invest in carbon dioxide removal.”

The missing millions—talking biodiversity

Aotearoa New Zealand is home to tens of thousands of unique animal and plant species, but their survival is threatened by climate change and rising sea temperatures, as well as introduced pests.

graphic image with kereru on one side, rat on another, plus other native animals on branches framing a beach scene
In this podcast, Master’s students Ellen Carlyon and Tessa Thomson (Ngāti Tukorehe, Ngāti Raukawa ki te Tonga) from the School of Biological Sciences join Dr Sarah-Jane O’Connor from the Centre for Science and Society to look at biodiversity in Aotearoa and how we can play a part in the protection of our forest and marine ecosystems for generations to come.

Species common in Aotearoa just two to three generations ago—including the Toheroa, a taonga shellfish which is the focus of Tessa’s thesis—have been commercially overfished, and are now rarely seen. Further inland, our native species are being decimated by rats and stoats.

“There are incredible numbers of pest species in our bush—you go there and see how quiet it is when it shouldn’t be quiet. You shouldn’t be able to hear yourself think because there’s so many birds,” says Ellen.

It’s a gloomy picture but the researchers say meaningful change can be achieved through the combined benefits of technology, from novel radio tracking technology and aquaculture, to drawing on people power and mātauranga Māori (Māori knowledge).

Tessa, who is completing her Master of Science in Marine Biology says the Toheroa was once a regular feature on her hapu’s menu. “We were known for them. When people would come to our marae, we’d serve Toheroa fritters, or soup. They were a massive part of our hapu’s way of life … my grandad doesn’t remember there ever not being any―and yet I’ve never seen a live one.”

Looking after the oceans to ensure kaimoana remain a viable source of protein for New Zealanders must involve conversations with local iwi about what they understand about ecosystems and how species interact, she says.

Ellen, who is completing a Master of Science in ecological restoration and leads the Aorangi monitoring project in South Wairarapa, agrees and says, “historically and globally, Western science hasn’t recognised the value in traditional ecosystem knowledge and that is an utter mistake”.

Heartened by the community spirit generated after the Government announced Predator Free 2050, she believes there is “something nice about a big dream and a whole country rallying together”.

“I would like listeners to know it’s not hopeless. It does seem pretty grim sometimes … but there’s definitely still hope, and science and ecology needs your voice.”

Marine heat wave linked to death of Fiordland sponges

Warming waters may already be taking a toll on marine sponges.

Marine sponge with patches of white
A sponge in Te Puaitaha—Breaksea Sound with patches of white, showing the start of bleaching. Sponges are normally dark brown. Photo credit: Charlie Bedford.

Warming waters in Fiordland could be responsible for the loss of up to 10 percent of one of the most abundant marine sponges in Pātea—Doubtful Sound. More sponges may have been lost further south in Tamatea—Dusky Sound and Te Puaitaha—Breaksea Sound.

Widespread bleaching of sponges (Cymbastella lamellata) was discovered in May 2022 by researchers from Te Herenga Waka—Victoria University of Wellington. This bleaching was linked to an extreme marine heatwave and affected millions of sponges.

Marine biologist Professor James Bell led a return trip to Fiordland this summer with Dr Valerio Micaroni and PhD candidate Ms Francesca Strano to investigate what had happened to the sponges. They found mixed results.

“At the six sites we surveyed in Pātea—Doubtful Sound, we found nearly all the sponges had recovered their colour and were no longer bleached—that’s the good news. However, some sponges are likely to have died. It’s hard to say how many have been lost but we think it could be 5 to 10 percent, based on video and photographic data,” Professor Bell says.

Early reports from the Southern Fiordland Initiative suggest the situation might be even worse in Dusky and Breaksea Sounds. The Initiative, co-led by Professor Bell, was launched in 2021 to monitor environmental changes in the fiords.

“Initial surveys in Breaksea Sound by Katherine Mitchell from the Southern Fiordland Initiative suggest a much lower number of sponges than seen last year and many of the sponges have not fully recovered from the bleaching.”

There are recent reports from Breaksea Sound of newly bleaching sponges, Professor Bell says.

Near the end of their trip to Doubtful Sound, the researchers also found some sponges were showing signs they might be starting to bleach again. Fiordland experienced another severe heatwave in late December and through much of January, with temperatures in some areas more than 5ºC warmer than normal.

Professor Bell says the bleaching itself does not appear to kill the sponges directly, but it seems to make them more susceptible to being eaten by fish.

“When we visited Fiordland in May last year, we saw sponges with lots of large bite marks in them. We didn’t see this on our latest trip, suggesting these sponges have died or been eaten, since it’s unlikely they could have regenerated the tissue they lost in such a short period of time—and we didn’t see sponges with deformities from regrowth.”

The researchers have discovered the bleaching causes the sponges to lose their photosynthetic diatoms—tiny symbiotic organisms that live inside the sponges.

“We believe it’s the loss of these diatoms that either makes the sponges more palatable to fish or makes them more visible to fish,” Professor Bell says.

The bleaching and sponge deaths may have other flow-on effects on the local marine environment.

“We’ve found evidence that sponges get food from their symbiotic diatoms and there’s a very strong likelihood the sponges release excess carbon produced by these diatoms. This carbon will be eaten by other organisms, particularly microbes in the seawater, fuelling local food webs. However, this food source isn’t available when sponges are bleached, removing a potentially important nutrient from the wider marine ecosystem.”

Further work is now underway at the University’s Coastal Ecology Laboratory to assess the effects of rapidly warming waters on sponges in the Fiordland region.

“Back in the lab, we’re going to replicate the conditions the sponges experienced in May 2022 so we can gauge what impact marine heat waves have on a wider range of sponge species.”

The team will be revisiting Dusky and Breaksea Sounds in late March to assess the extent of the decline in sponge populations.

Their visit to Doubtful Sound in January 2023 was on board the Department of Conservation (DOC) vessel Southern Winds. Richard Kinsey, marine senior ranger for DOC, was also on board assisting Professor Bell.

“The work that James is doing is vitally important to help us understand what future impacts might occur in the fiords so we can try to manage them. He’s the expert so it is great for us to be able to provide a vessel for him to work off so we can see what’s happening first-hand,” Mr Kinsey says.

The research work is supported by DOC, the George Mason Charitable Trust, the Fiordland Lobster Company, and The Leslie Hutchins Conservation Foundation.

Ant raids decimating honeybee colonies

Researchers from Te Herenga Waka—Victoria University of Wellington have demonstrated a link between invasive ant species and increased levels of diseases in bees.

A honey bee emerging from its hive being attacked by ants.
A honey bee worker emerging from a brood cell that is overrun by Argentine ants. Photo credit: Phil Lester.

PhD student Jana Dobelmann, from the University’s School of Biological Sciences, led the study, published this week in the journal Biology Letters.

Her research shows that when Argentine Ants invade bee colonies, there are higher levels of Deformed Wing Virus (DWV)—infamous for causing the death of millions of hives around the globe.

“Ants will raid beehives, kill off the bees, and take the honey—they’re predators.

“But what we’re also seeing is that even if the raid doesn’t necessarily spell the end of a hive, it can still result in extremely high viral loads causing severe infections and stress for the bees.”

Argentine Ants carry substantial levels of DWV, so Jana says it’s possible that they’re directly infecting the bees during a raid, or that the stress from the raid itself is inducing the higher infection loads.

Regardless, Jana says the effects of these ant invasions on local beehives can be deadly.

“DWV is one of the most dangerous pathogens affecting our bee colonies in New Zealand.

“It increases mortality, and high levels of infection can stunt a bee’s wing growth or result in learning difficulties. Bees with severe infections contribute little to the colony, so they are shunned and tossed out of the hive by other bees where they are left to die.”

Jana’s supervisor, Professor Phil Lester says that New Zealand’s native ants don’t have the same effect on the bee population.

“We haven’t seen native ants attacking beehives at all. Our research has only shown introduced species exhibiting this destructive behaviour.”

Argentine Ants were first found in New Zealand in the 1990s and have since spread around the country.

With honey worth hundreds of millions of dollars to the New Zealand economy, and critical to our nation’s biodiversity, Professor Lester says more needs to be done.

“Currently, the only option available to beekeepers are pesticides that are widely toxic. Many beekeepers are forced to abandon apiary sites entirely—these ants and the viruses they spread are overwhelming.

“Shifting apiary sites can be a problem in itself though. If even a few ants are shifted with the apiary, you’ve just introduced the ants to a whole new area, and you’ll likely see the same thing happen again.”

Professor Lester says there’s no silver bullet on the horizon.

“We’re looking at different ways of trying to control the effects of pathogens including DWV.

“One of our current projects is with immunotherapy—creating antibodies to try to cure or curtail this deadly virus in honey bees.”

See the article ‘An invasive ant increases deformed wing virus loads in honey bees’ by Dobelmann et al., published in Biol. Lett.

Rare native fish spotted in Wellington Harbour

Marine researchers snap photo of rare fish.

Scaly gurnard in Wellington Harbour
Scaly gurnard photographed in Wellington Harbour.

A rare native fish has been photographed in Wellington Harbour and researchers believe it’s one of the few times the species has been caught on camera in its natural habitat.

Dr Valerio Micaroni, a marine biologist at Te Herenga Waka—Victoria University of Wellington, says the scaly gurnard is a reddish-coloured fish that grows to about 20 centimetres. It’s known to live in Wellington waters but sightings are rare.

The fish was spotted by Dr Micaroni and colleague Francesca Strano while they were exploring the animal communities that live in the shallow waters (<30 metres) around Wellington. Its identity was confirmed by Dr Malcolm Francis, a fish biologist and author of Coastal Fishes of New Zealand.

“There’s very little information about the location and composition of the animal-dominated habitats in Wellington’s waters, so the aim of our research is to describe these areas and identify places that need protection or restoration,” Dr Micaroni says.

Five sites in the harbour have been mapped so far.

“As well as the scaly gurnard, we’ve found lots of other cool animals. At Shark Bay and Shelly Bay on the Miramar Peninsula, there’s a diverse underwater garden of sea sponges. Horse mussels and brachiopods—ancient animals that live on the sea floor—are also abundant.”

Sponge gardens, which are typically found near the shore at depths of between seven and 15 metres, have also been identified at sites at Evans Bay, Kaiwharawhara and west Petone. However, these sites are heavily impacted by high levels of sedimentation.

Another sponge garden and a red algae bed were found at Mahanga Bay.

Ms Strano says the areas were initially explored using a remotely operated underwater vehicle (ROV). Detailed information about the habitats and the animals they support was then collected by diving at the sites.

“So far, we’ve sent the ROV on 52 dives. That’s given us a lot of valuable data about these ecosystems and the threats they face,” she says.

“Lots of people have looked at the seaweed and kelp-dominated areas in the harbour, but there’s little data on the animal-dominated ecosystems so this project aims to figure out where they are.”

The research is funded by the Greater Wellington Regional Council and the George Mason Charitable Trust, which provided funding for the ROV. Data collected will be used to inform the council’s marine policy and planning processes.