Lauren Fuge
A snorkeller has been attacked by a ray while conducting a marine survey, which biologists say might be linked to oceanic algal blooms.
The incident occurred on the Yorke Peninsula in South Australia, west of the capital city, Adelaide. The snorkeller was conducting a marine survey when the ray pierced her arm and left a 16cm barb in it. She was airlifted to Adelaide for surgery.
The marine biologist who reported the incident, Dr Mike Bossley, says thousands of dead and dying fish, sharks and rays have washed up along Yorke Peninsula beaches.
Bossley, who was leading the survey team of citizen scientists, suggests that this mortality event – and possibly the attack – may be linked to the algal bloom that has been spreading across the unseasonally warm waters of South Australia.
This is likely the same algal bloom that has been wreaking on marine life and beachgoers alike hundreds of kilometres away on the Fleurieu Peninsula, south of Adelaide, from March onwards.
“I’ve snorkelled and dived with eagle rays dozens of times over the years, and never experienced behaviour like this from them,” says Bossley, who has worked in the area since 1978.
“They are typically a shy and placid species, but it seems the algal bloom has caused such severe distress that it has changed their behaviour completely.
“I’ve never seen anything remotely like this before.”
Ray attack
The incident occurred on Friday May 2 at Treasure Cove, a marine sanctuary near Marion Bay that is only accessible through private property. Bossley and team regularly snorkel in the area, and visited last week to see how the marine life is coping with the recent algal bloom.
“We went for a walk along the beach on the Thursday afternoon and found lots of dead things,” Bossley says.
Thousands of cuttlefish bones had washed up, as well as fish in smaller numbers including leather jackets, toad fish, porcupine fish and cow fish. Bossley and team also found dead Port Jackson sharks and fiddler rays.
“On the Friday we decided to go into the water at Treasure Cove to have a closer look at what it was like underwater,” he says.
In particular, they planned to see if there was any effect on sessile creatures like sea anemones that couldn’t move away from hostile conditions.
But the survey had to be abandoned quickly.
“We had no sooner got in the water than we encountered these big rays that became very aggro,” Bossley says.
Many rays were present in the cove, which is unusual in itself, and two approached the survey group, which was even more unusual. Bossley suspects they were eagle rays, but did not have time to identify them.
Within minutes, one snorkeller had been attacked and was bleeding profusely from her arm, which had been pierced by a barb. The team immediately evacuated the water to seek medical attention.
It is unclear why the rays acted aggressively.
“Whether their sensitivities were heightened in some way, and they felt we were a threat, I don’t know,” Bossley says.
The open question is whether the behaviour is linked to the algal bloom, and if so, what mechanism is driving the behaviour.
“It’s possible – a lot of fish have died from the toxin and/or from having their gills coated,” Bossley says. “That may be impacting the sharks and rays, or it may be that there’s some behavioural, psychological impact from the toxin … making them more aggressive.”
No necropsies have yet been conducted on sharks or rays to see how the algae affects them.
Bossley also suspects that those still alive in the water may be in severe pain and in distress.
His team also reports seeing a 3-metre shark swimming barely two metres off the beach on Thursday May 1, which is “a very unusual and potentially dangerous behaviour”.
“People should be very careful about going into the water,” Bossley says. “The behaviour of sharks and rays seems to have been impacted by the by the algal bloom, and they’re behaving in strange and potentially unpredictable ways, and that could be a threat to human life.”
Strange tides
As Cosmos has previously reported, this recent algal bloom was first seen on the Fleurieu Peninsula, 100km south of Adelaide.
On March 17, thousands of dead fish washed up on Waitpinga and Parsons Beach, accompanied by strange foam. Dozens of surfers and beachgoers then reported flu-like symptoms.
A joint investigation between the Environment Protection Authority (EPA), the Department of Primary Industries and Regions South Australia (PIRSA) and the Department for Environment and SA Health confirmed that the marine deaths were caused by an algae (Karenia mikimotoi). This can be toxic to fish and invertebrates, and cause non-fatal reactions in humans.
Also called phytoplankton, microscopic marine algae occurs naturally across the world’s oceans and produces a vast percentage of the oxygen in our atmosphere. But in certain conditions, one species can dominate over others and cause an algal bloom. In this case, the spread of Karenia mikimotoi was caused by warm, still conditions.
As the EPA stated at the time: “The event has been driven by an ongoing marine heatwave, with marine water temperatures currently 2.5C warmer than usual, as well as relatively calm marine conditions with little wind and small swell.”
PIRSA added: “The bloom is expected to remain present until the state receives strong westerly winds, which historically start around the end of April. Nothing can be done to dilute or dissipate the bloom.”
As early as mid-April, there were further reports of dying fish across the SA coast, from Kangaroo Island to Edithburgh on the Yorke Peninsula. Though tests are not yet conclusive, it is suspected that these are linked to the same algal bloom, spread along the coastline.
Satellite imagery has shown increased chlorophyll levels around the state, which allows scientists to map phytoplankton (algae). Over the last few months, this mapping data shows the algal bloom spreading westward from the Fleurieu to Kangaroo Island and the eastern and southern Yorke Peninsula.
Observations of dead fish continue to roll in, and the warm conditions continue.
Bossley says this current marine heatwave is unusual in its intensity and duration.
“I have been diving on the southern Yorke Peninsula for almost 50 years, and this is by far the most severe situation I have seen,” he says.
“If anyone doubts the impact of climate change, they should drive to one of the beaches down there and take a look. And in coming years it’s only going to get worse.”
It is still not settled whether warming waters will increase the likelihood of harmful algal blooms. Some research suggests that climate change has driven an intensification of blooms around North America, but more local research is needed.
Community observations count
To help monitor the ongoing marine mortality event, PIRSA encourages beachgoers “to report any marine mortalities to FISHWATCH on 1800 065 522 so they can be added to the testing regime being carried out by PIRSA”.
Fishing conservation group OzFish is also urging people to become citizen scientists and upload pictures of dead fish and marine animals to publicly accessible databases such as iNaturalist, where public contributions have already identified more than 100 species impacted by the mortality event.
“[Citizen science] can be really helpful in tracking the progress of the bloom, both in time and space, and also tracking the species that are impacted by it,” Bossley says. “I think citizen science, in this case, can be very provide very useful information.
“What it doesn’t do, of course, is provide any solutions. But that’s political.”
Dr Nick Whiterod, science program manager at the Coorong Lower Lakes and Murray Mouth Research Centre, agrees that community input in these situations is important.
“The current marine algal bloom is a great example of community getting engaged and making a difference to better understand what is going on and what is being impacted,” says Whiterod, who has been engaging with the community around the southern Fleurieu region.
“This needs to continue and expand so that community and First Nations work alongside with management agencies and research to better understand how climate change will impact and how we can collectively prepare for future changes”.
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