Deadly algal bloom in South Australia’s Coorong an environmental ‘eye opener’, ecologist says

 

 

Dead and dying polychaete worms at the southern end of Coorong’s North Lagoon. Photograph: Glen Hill

by Petra Stock

 Among the dead in the internationally significant wetland are estuarine snails, shore crabs, baby flounder and ‘a thick stew of polychaete worms’

 

When South Australia’s algal bloom arrived in the Coorong, it stained the water like strong tea before turning it into a slurry of dead worms.

Many had hoped the storm in late May would break up the bloom of Karenia mikimotoi algae, which has killed more than 200 different marine species. Instead, high tides swept the algae into the Coorong, an internationally significant Ramsar wetland at the mouth of the Murray River.

Once there, the algae began “reproducing madly” in the nutrient rich waters of the North Lagoon, according to estuarine ecologist Faith Coleman.

Among the dead were mostly benthic species – estuarine snails, shore crabs, baby flounder and “a thick stew of dead polychaete worms” – a crucial food source for shorebirds and fish.

 

Levels had declined from their peak but the smell of rotting fish remained, along with algal spores buried in the sediment. “As soon as it warms up again, the likelihood is [the algal bloom will] be back,” Coleman said.

The marine heatwave, a contributing factor to the bloom, persisted off the coast of SA, according to an 11 June update, which showed increases in chlorophyll – an indicator of algae concentrations – along the Coorong coast and western Gulf Saint Vincent.

Fourth generation fisherman Gary Hera-Singh was one of the first to notice the lagoon’s colour turn a “dark, orangey-brown”.

“We had a big storm event, a lot of seawater got pushed around, and this algal bloom found its way into the Coorong and has just created havoc since,” he said, and there were still “massive patches – 100 acres at a time” where the bloom was flourishing.

Hera-Singh has witnessed the health of the Coorong decline in his lifetime, but said in 41 years of fishing the impact of the algal bloom was the worst event he had seen.

The Coorong, a 120km narrow band of water separated by sand dunes from the Southern Ocean, together with lakes Alexandrina and Albert, is considered a wetland of international significance, providing critical habitat for fish, water birds and many threatened species. The North Lagoon – the area affected – is an important nursery for fish such as mulloway and bream.

 Prof Peter Gell, an expert in Ramsar listed wetlands, said the wetlands had degraded over a long period of time, with barrages (structures that control water flow) added in the 1950s, higher nutrient loads and extended periods of reduced flow from the Murray.

 

Algal blooms were symptoms of broader changes, he said. “Because of this we’re seeing – both offshore and within the Coorong – substantial changes in the food web.”

As a wetland of international significance, the Australian government was obliged to report environmental changes to the Coorong under the Ramsar convention, Gell said, a process that usually triggered restoration efforts.

Federal and state governments were liaising about the situation, including any long-term impacts likely to affect the ecological character of the Coorong, a federal environment department spokesperson said.

“We understand that, given the dynamics of the North Lagoon, it is difficult to dissipate the bloom and it might remain for some time.”

Fresh water may help the situation, Coleman said, given the algae thrived at salinity levels of 18-37 grams per litre. Restoration efforts would help build the resilience of the Coorong and marine areas, she said.

The system was already under pressure, said Dr Nick Whiterod, an ecologist and science program manager at the Coorong Lower Lakes Murray Mouth Research Centre. But the recent drought and unusual algal blooms had been “eye openers” to many people, he said.

Last year, a tropical species of blue-green algal bloomed in Lake Alexandrina for the first time, and had persisted, Whiterod said. Now that karenia mikimotoi had got into the Coorong, there was concern it too would bloom again.

The Coorong was vulnerable to the impacts of climate change, like sea level rise and reduced river flows, he said.

“Ocean temperatures are heating up. It’s creating conditions that are conducive to algal blooms all around the world,” he said. “Our ecosystems are really stressed, we are getting to a period of time where some may not have the capacity to recover.”

 

‘Ticking timebomb’: sea acidity has reached critical levels, threatening entire ecosystems – study. Ocean acidification has already crossed a crucial threshold for planetary health, scientists say in unexpected finding.

As scientists looked deeper into the ocean, they found worse levels of acidification. Photograph: DrPixel/Getty Images

 Lisa Bachelor

The world’s oceans are in worse health than realised, scientists have said today, as they warn that a key measurement shows we are “running out of time” to protect marine ecosystems.

Ocean acidification, often called the “evil twin” of the climate crisis, is caused when carbon dioxide is rapidly absorbed by the ocean, where it reacts with water molecules leading to a fall in the pH level of the seawater. It damages coral reefs and other ocean habitats and, in extreme cases, can dissolve the shells of marine creatures.

Until now, ocean acidification had not been deemed to have crossed its “planetary boundary”. The planetary boundaries are the natural limits of key global systems – such as climate, water and wildlife diversity – beyond which their ability to maintain a healthy planet is in danger of failing. Six of the nine had been crossed already, scientists said last year.

 

However, a new study by the UK’s Plymouth Marine Laboratory (PML), the Washington-based National Oceanic and Atmospheric Administration and Oregon State University’s Co-operative Institute for Marine Resources Studies found that ocean acidification’s “boundary” was also reached about five years ago.

“Ocean acidification isn’t just an environmental crisis – it’s a ticking timebomb for marine ecosystems and coastal economies,” said PML’s Prof Steve Widdicombe, who is also co-chair of the Global Ocean Acidification Observing Network.

The study drew on new and historical physical and chemical measurements from ice cores, combined with advanced computer models and studies of marine life, which gave the scientists an overall assessment of the past 150 years.

It found that by 2020 the average ocean condition worldwide was already very close to – and in some regions beyond – the planetary boundary for ocean acidification. This is defined as when the concentration of calcium carbonate in seawater is more than 20% below preindustrial levels.

The deeper in the ocean they looked, the worse the findings were, the scientists said. At 200 metres below the surface, 60% of global waters had breached the “safe” limit for acidification.

“Most ocean life doesn’t just live at the surface,” said PML’s Prof Helen Findlay. “The waters below are home to many more different types of plants and animals. Since these deeper waters are changing so much, the impacts of ocean acidification could be far worse than we thought.”

This had, she added, huge implications for important underwater ecosystems such as tropical and even deep-sea coral reefs that provided essential habitats and nursery grounds for the young of many species.

As pH levels drop, calcifying species such as corals, oysters, mussels and tiny molluscs known as sea butterflies struggle to maintain their protective structures, leading to weaker shells, slower growth, reduced reproduction and decreased survival rates.

 

The authors underlined that decreasing CO₂ emissions was the only way to deal with acidification globally, but that conservation measures could and should focus on the regions and species that were most vulnerable.

Jessie Turner, director of the International Alliance to Combat Ocean Acidification, who was not involved in the study, said: “This report makes it clear: we are running out of time and what we do – or fail to do – now is already determining our future.

“We are coming to terms with an existential threat while grappling with the difficult reality that much suitable habitat for key species has already been lost. It’s clear that governments can no longer afford to overlook acidification in mainstream policy agendas,” she said.

 

See How Marine Heat Waves Are Spreading Across the Globe
 

Planet’s darkening oceans pose threat to marine life, scientists say. Band of water where marine life can survive has reduced in more than a fifth of global ocean between 2003 and 2022

Changes in global photic zones between 2003 and 2022 are shown with red areas to indicate ocean darkening and blue lightening. Illustration: Thomas Davies/University of Plymouth

Ian Sample Science editor

 

 

Great swathes of the planet’s oceans have become darker in the past two decades, according to researchers who fear the trend will have a severe impact on marine life around the world.

Satellite data and numerical modelling revealed that more than a fifth of the global ocean darkened between 2003 and 2022, reducing the band of water that life reliant on sunlight and moonlight can thrive in.

The effect is evident across 75m sq km (30m sq miles) of ocean, equivalent to the land area of Europe, Africa, China and North America combined, and disturbs the upper layer of water where 90% of marine species live.

Dr Thomas Davies, a marine conservationist at the University of Plymouth, said the findings were a “genuine cause for concern”, with potentially severe implications for marine ecosystems, global fisheries and the critical turnover of carbon and nutrients in the oceans.

 

Most marine life thrives in the photic zones of the world’s oceans, the surface layers that allow sufficient light through for organisms to exploit. While sunlight can reach a kilometre beneath the waves, in practice there is little below 200 metres.

This upper band of water is where microscopic plant-like organisms called phytoplankton photosynthesise. The organisms underpin virtually all marine food webs and generate nearly half the planet’s oxygen. Many fish, marine mammals and other creatures hunt, feed and reproduce in the warmer waters of the photic zones where food is most abundant.

Davies and his colleagues drew on satellite data and an algorithm used to measure light in sea water to calculate the depths of photic zones around the world. Darkening affected 21% of the global ocean in the 20 years to 2022. In 9% of the ocean, this led to photic zones being 50 metres shallower, while in 2.6% of the ocean, the zones were 100 metres shallower. Details of this study appear in Global Change Biology.

The oceans darken when light finds it harder to penetrate the water. It is often seen along coastlines where upwellings of cold, nutrient rich water rise to the surface, and where rainfall sweeps nutrients and sediments from the land into the water.

The drivers for darkening far offshore are less clear, but global heating and changes in ocean currents are thought to be involved. “The areas where there are major changes in ocean circulation, or ocean warming driven by climate change, seem to be darkening, such as the Southern Ocean and up through the Gulf Stream past Greenland,” Davies said.

 

Despite an overall darkening, about 10% of the ocean, or 37 million sq km, became lighter over the past 20 years, the study found. Off the west coast of Ireland, for example, a very large area of ocean has brightened, but further out it has darkened.

“Marine organisms use light for a whole variety of purposes. They use it for hunting, for mating, for timing reproductive events. They use it for basically every single part of their biology,” said Davies. “With ocean darkening, they have to move up the water column, and there is less space, they’re all being squished up towards the surface.”

Prof Oliver Zielinski, the director of the Leibniz Institute for Baltic Sea Research in Germany, said the darkening of vast ocean areas was a “worrying trend”.

“Such changes can disrupt marine food webs, alter species distributions, and weaken the ocean’s capacity to support biodiversity and regulate climate,” he said. “Coastal seas, being closest to human activity, are particularly vulnerable, and their resilience is crucial for both ecological health and human wellbeing.”

 

‘A horror movie’: sharks and octopuses among 200 species killed by toxic algae off South Australia

 

A dead shark found on a beach in South Australia is among dozens of marine species killed by a toxic algal bloom. Photograph: L Cameron

 Petra Stock

 Karenia mikimotoi algae can suffocate fish, cause haemorrhaging and act as a neurotoxin, one expert says

 

More than 200 marine species, including deepwater sharks, leafy sea dragons and octopuses, have been killed by a toxic algal bloom that has been affecting South Australia’s coastline since March.

Nearly half (47%) of the dead species were ray-finned fish and a quarter (26%) were sharks and rays, according to OzFish analysis of 1,400 citizen scientist reports.

Cephalopods – such as squid, cuttlefish and octopuses – accounted for 7%, while decapods – crabs, lobsters and prawns – made up 6% of species reported dead or washed up on beaches.

The OzFish South Australian project manager, Brad Martin, said the harmful bloom – of Karenia mikimotoi algae – was like a toxic blanket that smothered marine life.

 

“It can suffocate fish from their gills, cause haemorrhaging by attacking their red blood cells, and act as a neurotoxin and attack the fish’s nervous system and brain, causing unusual behaviour,” he said.

“This is why some fish and sharks are acting so strangely and why many of the dead have a red tinge – it is like a horror movie for fish.”

According to the state’s environment department, the algal bloom was being driven by an ongoing marine heatwave – with water temperatures 2.5C hotter than usual – as well as relatively calm marine conditions with little wind and small swells.

While not toxic to humans, the algae could cause skin irritations and respiratory symptoms, and caused mass mortalities in marine life.

The algae was first identified in mid March on the state’s Fleurieu Peninsula and had since expanded to coastlines across the south-east, the Gulf St Vincent, the Yorke Peninsula and Kangaroo Island, Martin said.

 

OzFish, an organisation dedicated to restoring waterways and fish habitats, was concerned about the long-term impact on fisheries, given the bloom had killed fish at all ages – from fingerlings, or baby fish, up to full-grown breeding fish – as well as their food sources.

Several oyster farms and the commercial harvesting of pipis have been temporarily closed due to the outbreak, which has been unprecedented for South Australia, its environment minister, Susan Close, said.

“We’re talking about a very large algal bloom with a significant impact on marine life,” she said, with some parts of the outbreak going 20 metres deep.

Marine biologist Prof Shauna Murray from the University of Technology Sydney – who identified the algae under the microscope and by analysing its DNA – said there were about 100 species of harmful algae, each with a different toxic effect.

 

While still not well understood, Karenia mikimotoi was thought to produce a reactive oxygen that caused gill cell damage in fish – which meant they could not breathe, Murray said.

While the current bloom extended for more than 150km, it was not the worst in Australia’s history. In 2013, a bloom of a different species, Alexandrium catenella, had “covered the entire east coast of Tasmania and shut down their aquaculture and seafood industries for about four months”, she said.

Large blooms could also reduce the amount of oxygen in the water, said Prof Martina Doblin, a UTS oceanographer who specialises in algal blooms.

Karenia mikimotoi is an unusual algae that could feed on sunlight as well as other organisms, she said. And it is these characteristics, combined with unusually high and stable water temperatures, that enabled the algal bloom to become so large and sustained.

“In low abundance, it is part of the natural food web. But in high abundance, it can become very problematic,” Doblin said.

Such events were rare, but they can be devastating for local economies, she said. Improved early warning systems and management had the potential to limit the damage.

Strong westerly winds were ultimately needed to dissipate the algae, according to a spokesperson for SA’s environment department. “However, persistent high-pressure systems affecting southern Australia have delayed these winds,” they said.

 

Ningaloo and Great Barrier Reef hit by ‘profoundly distressing’ simultaneous coral bleaching events

 Footage shows coral bleaching on Ningaloo reef as Great Barrier Reef hit at the same time – video

 Scientists say widespread damage to both world heritage-listed reefs is ‘heartbreaking’ as WA reef accumulates highest amount of heat stress on record

 Graham Readfearn

Great Barrier Reef

 Ningaloo
 

 

Australia’s two world heritage-listed reefs – Ningaloo on the west coast and the Great Barrier Reef on the east – have been hit simultaneously by coral bleaching that reef experts have called “heartbreaking” and “a profoundly distressing moment”.

Teams of scientists on both coasts have been monitoring and tracking the heat stress and bleaching extending across thousands of kilometres of marine habitat, which is likely to have been driven by global heating.

 

On the Great Barrier Reef, bleaching is being detected from around Townsville to the tip of Cape York, a distance of about 1,000km.

On Western Australia’s famous Ningaloo reef, waters have accumulated the highest amount of heat stress on record during an extended marine heatwave that has hit coral reefs all along the state’s vast coastline.

Paul Gamblin, the chief executive of the Australian Marine Conservation Society, said history would “record this profoundly distressing moment” when two world famous reefs both suffered widespread damage at the same time.

Corals begin to bleach at about 4DHW, and 8DHW can kill heat-sensitive corals. Scientists say levels up to 16DHWs have been detected on the Ningaloo coast. Photograph: David Juszkiewicz/Curtin University

Dr Zoe Richards, an associate professor and coral scientist at Curtin University, spent 10 days monitoring the health of Ningaloo reefs and the neighbouring Exmouth Gulf earlier this month.

She said in shallower areas known for their clear waters, which are popular with tourists, she had seen up to 90% of corals bleached and evidence of corals dying. Even slow-growing corals that were hundreds of years old were bleaching, she said.

Ningaloo last experienced widespread bleaching only three years ago.

 

The WA government, which is coordinating monitoring across reefs there, said bleaching had also been reported at Kimberley, Ashmore Reef, Rowley Shoals, Barrow Island, Dampier Archipelago, inshore Pilbara and Exmouth Gulf.

Richards said: “This isn’t isolated to Ningaloo – this is happening across the entire north-west shelf. There has never been this scale of impacts in WA. I am not aware of this ever happening before. Climate change has definitely caught up with the reefs in WA.”

Corals lose the algae that give them their colour and most of their nutrients if ocean waters get too warm. If bleaching is not severe, corals can recover, but studies show they are less able to reproduce and are more susceptible to disease.

Coral reef experts use a metric known as degree heating weeks (DHW) to show how much heat corals have accumulated. Generally, corals begin to bleach at about 4DHW, and 8DHW can kill heat-sensitive corals.

Dr Jessica Benthuysen, an oceanographer at the Australian Institute of Marine Science (Aims), first saw signs of heat accumulating in WA last August. By the end of December, she said, some areas had sea surface temperatures 4C hotter than normal.

Benthuysen said levels up to 16DHWs had been detected on the Ningaloo coast, which were the highest on record.

Bleaching at Lakeside Reef Front, Ningaloo. Paul Gamblin of the AMCS says scientists have warned of widespread damage from underwater heatwaves and cyclones to both reefs ‘for decades’. Photograph: Zoe Richards/Curtin University

Coral bleaching at Mesa Back Reef at Ningaloo in WA. Photograph: Chris Fulton/Australian Institute of Marine Science

The US government’s Coral Reef Watch says DHWs between 12 and 16 are enough to cause coral death across multiple species.

The federal government’s Great Barrier Reef Marine Park Authority has coordinated monitoring flights over northern reefs, finding low to high levels of bleaching on most reefs. Underwater checks found bleaching at 24 of 30 reefs surveyed.

Bleaching was worse farther north – there is no concern for reefs in the park’s southern section.

Last summer was the worst bleaching event on record for the reef and the fifth major outbreak in eight years, hitting all across the marine park.

Dr Neal Cantin, a coral reef biologist at Aims who was on the monitoring flights, said bleaching was generally worse closer to shore but there was “high to medium” bleaching on reefs from Cairns to the far north. He said in the far north, heat stress was between six and 13DHWs, which was “capable of causing mortality”.

Dr Roger Beeden, the chief scientist at the authority, said detailed analysis of the data from the flights was still being analysed, but he said the lack of recovery time for corals between major events was worrying.

“It’s the frequency as well as the severity that makes us most concerned,” he said.

Dr Emily Howells, a coral scientist from Southern Cross University who has been at the Australian Museum’s research station on Lizard island since February, said this was now the sixth summer in a row that bleaching had been seen there.

The island, in the north of the reef, was badly hit by bleaching last summer and scientists at Aims who visited in subsequent months said the area had lost one-third of its live corals due to the heat.

Howells said there was less coral mortality this year, “but that’s because a lot of the sensitive corals died last summer”.

“There just isn’t enough opportunity for these coral communities to bounce back. It’s heartbreaking,” she said.

“We’re making it more and more challenging for the corals. The solution is having stronger action on climate change. The longer we wait, the worse it will get.”

 

Northern parts of the Great Barrier Reef have also been heavily affected by flooding from torrential rains. James Cook University’s TropWATER group has recorded flood waters carrying sediments and nutrients in a plume across 700km of the coast and extending as far as 100km offshore.

Jane Waterhouse, a reef water quality expert at TropWATER, said major flood events appeared to be happening more often and flood plumes were reaching farther offshore.

“River discharge carries pollutants, sediments and nutrients,” she said. “You get muddy water that cuts the light that seagrass and corals need to grow, and that nutrient also allows algae to grow.”

Gamblin said the widespread damage from underwater heatwaves and cyclones to both reefs was “what our world-renowned scientists have been warning us about for decades”.

He said fossil fuel companies were “doubling down” to get more mega projects running, pointing to areas around Scott Reef in WA being targeted for expansion by Woodside.

He said: “More mega polluting projects up at places like Scott Reef will make a tragic situation worse. What will our children say to us?”