3 days ago
Hopes high after ocean temperatures off SA coast drop amid algal bloom outbreak
Ocean temperatures off South Australia's coast have dropped following storms this week, sparking hopes the toxic algal bloom will soon end.
Offshore buoys looked after by Flinders University, which measure sea surface temperature, show it has dipped below 16 degrees Celsius at Robe for the first time in about two months.
Ocean temperatures have also dropped near Adelaide and Victor Harbor.
A buoy at West Beach recorded sea surface temperatures of 15.38C yesterday after reaching 16.56C on Sunday. A buoy at Victor Harbor saw a drop from 17.28C on Sunday to 16.56 yesterday.
It follows a marine heatwave which saw ocean temperatures 2.5C warmer than usual, which led to an algal bloom outbreak spanning thousands of kilometres.
Flinders University coastal studies professor Patrick Hesp said the drop was a glimmer of good news amid the bad weather which saw thousands without power, jetties damaged and coastal erosion.
"We've seen quite significant erosion, but perhaps one of the positive effects is that there would be a significant amount of mixing because of those big waves," Professor Hesp said.
In March, surfers reported sore eyes, coughing and blurry vision after visiting beaches west of Victor Harbor and since then marine life has been found dead along the eastern Yorke Peninsula, the Fleurieu Peninsula and Kangaroo Island.
The Environment Protection Authority (EPA) and the Department of Primary Industries and Regions South Australia (PIRSA) identified the cause of the irritation and deaths as Karenia mikimotoi, a toxic microalgal bloom.
PIRSA said water testing results to check whether the bloom had dissipated would be available early next week.
Marine biologist and UTS researcher Shauna Murray, who helped authorities identify the bloom in March, said storms could be a circuit breaker.
"Normally with strong weather conditions you would expect to see dissipation and things are being pushed out," she said.
However, she said it was difficult to predict what would happen with this bloom because of its size.
"It's complicated because it's a large bloom over a very big area," she said.
"It's hard to know to what extent it's now seeding itself and it's continuing to grow, and to what extent it's just being dispersed into certain areas."
Faith Coleman, an ecologist who has been testing water samples, said the weather would have flushed out waters — but the extent was not yet clear.
"It may have happened totally or it may have happened partially," she said.
"If it's only happened partially we may end up with bloom occurring, if we have sunny days after this, in places that [it hadn't]."
Wild weather was experienced throughout South Australia earlier in the week with waves up to 5.6 metres recorded by a buoy off Robe on Monday night, along with similar heights north of Kangaroo Island and slightly smaller swell offshore of Victor Harbor.
The strongest wind gust was 126 kilometres per hour, recorded at Neptune Island.
Roanna Horbelt, who runs Research and Discovery Coastal Tours, Kangaroo Island, took TAFE students out on the sea off Emu Bay on Wednesday.
After previously reporting dead fish and stingrays in the area, Ms Horbelt said the group was "very pleasantly surprised".
"There's still particles in the water for sure, but I mean hardly any foam at all and the amount of birdlife and other life that we're seeing around there are looking a lot happier."
The group saw a large pod of dolphins, along with hundreds of birds and seals.
Dolphins that had previously disappeared in cloudy water just 1.5 metres deep were now clearly visible.
"Yesterday, they seemed to be very joyful and back to normal and followed our boat for almost 20 minutes just riding the bow along the coastline, so we had about 80 of them doing that, so that was pretty special," Ms Horbelt said.
"Everything seemed almost back to normal, fingers-crossed."
Citizen scientist and aquatic instructor Lochie Cameron is one of the organisers of a forum on the effects of the algal bloom that is being held in Marion Bay, on the Yorke Peninsula, on Sunday.
He believed the algal bloom would have a long-lasting impact.
"I feel a bit grim about it," he said.
"I think we're looking at a couple of decades-long recovery for these areas.
"A lot of the species that have been impacted are long-lived species that take quite a long time to mature, so, yeah, I do hold quite a large concern for our sea dragons and boarfish and other benthic species as well."
