Lauren Fuge
People who live in coastal cities all across the world might not always be aware of the extent of scientific research going on around – and under – them, to preserve waterways for humans and animals alike.
For example, it’s been a big week for South Australian oceans – from the installation of high-tech buoys, to fish die-offs and surfer sickness, to a surprising discovery about the benefits of an introduced species.
Algae blooms and accurate buoys
Last week, dead fish, octopuses and sea dragons along with a mysterious brown sea foam began washing up along Waitpinga and Parsons Beach on the southern Fleurieu coast, 100 km south of the capital, Adelaide.
At the same time, more than 100 surfers and beachgoers in the region fell ill with flu-like symptoms.
Scientists have just confirmed that these occurrences were due to tiny planktonic algae called Karenia mikimotoi, which were found in high numbers in water samples taken from the beaches.
Also called phytoplankton, microbial algae naturally occur across the world’s oceans and produce a vast percentage of the oxygen in our atmosphere. But in certain conditions, one species can dominate over the others and cause an algal bloom.
In this case, it was K. mikimotoi – and unfortunately this species produces a toxin that is harmful to marine life and humans. These toxins are not fully understood, but they are known to damage the gills, gastrointestinal tracts and livers of fish. The species can also produce a thick substance that can cause sea foam, as seen on SA beaches.
An unanswered question is whether warming waters will increase the likelihood of harmful algal blooms, which can damage marine ecosystems and devastate coastal aquaculture. Some research suggests that climate change has driven an intensification of blooms around North America, but more local research is needed.
Luckily, Flinders University researchers have just installed two ocean-monitoring buoys in Encounter Bay, several kilometres east of the affected beaches. They join a network of buoys installed from Ceduna, 800km west of Adelaide, to Robe in the southeast, 350 km east of the capital.
These buoys will collect and transmit data in real-time, including wind speed and direction; wave height, period and direction; sea surface temperature; and barometric pressure.
“This will provide good baseline data about coastal waters that has been lacking, and there has never been a better time to have more information about this stretch of ocean,” says Miot da Silva, part of Flinders University’s Beach and Dune Systems (BEADS) Lab.
“There has been a significant gap in wave information available to researchers, managers, developers and policy makers. These buoys will make a huge difference.”
The data collected by these buoys will help scientists predict future changes in SA’s coastline, particularly as the oceans warm and the sea levels rise. This will hopefully also allow local governments to better protect local coastlines.
The data is freely available through the SA Waves website, which also includes information from the other buoys across the SA coastline.
Port River and Pacific oysters
Meanwhile, up in the mangrove-filled estuary around Adelaide’s Port River, the invasive Pacific oysters have been found to benefit biodiversity.
This is counter-intuitive, as most habitat managers go to great lengths to avoid invasive or non-native creatures.
“Pacific oysters were first detected in the Port River in 2009 during a regular PIRSA biosecurity monitoring, which discovered 6+ year-old hatchery stock,” explains lead researcher Brad Martin, who is a Flinders University PhD candidate. “This was a deliberate but unauthorised stocking attempt presumably to establish Pacific oysters.”
Introduced species can have significant effects on the way an ecosystem function. But as Martin reports in a new paper in the journal NeoBiota, the influence of the Pacific oyster (Magallana gigas) on local fish and invertebrates isn’t all bad.
“Through this research we found that these Port River oyster reefs are providing habitats for coastal animals,” says Martin.
Pacific oysters create complex structural habitats that make good homes, food sources and breeding locations for many other species. The new study found that the oyster habitats support eight times more biomass of mobile invertebrates (like crabs, worms and snails) when compared to other habitats.
This in turn creates more prey for native fish to feed on, which is significant because the mangroves of the Port River are fish nurseries.
“It also seems that the Pacific oyster shell is helping to trap and stabilise mangrove seedlings, potentially assisting their establishment,” Martin adds.
“While not quantified in our study, the oysters are filter-feeders and likely sequestering sediment, excess nutrients and pollutants from the water column.”
South Australia was once home to vast reefs of native oysters (Ostrea angasi), including throughout the Port River and Barker Inlet estuary. These were decimated during European colonisation due to dredge fishing. These reefs usually formed in the subtidal zone out to depths of 18 metres, while Pacific oysters prefer shallower water.
“This means that Pacific oysters, which prefer the upper intertidal zone, are not directly replacing our native oyster reefs,” Martin explains. “In the Port River context, Pacific oysters are potentially replacing intertidal mussel beds, and competing with endemic razor clams (or ‘razorfish’).”
But there are also downsides to the presence of the introduced oyster. For example, the habitats they create is also used by other non-native species, including European shore crabs, which are designated as a marine pest and like to eat native shellfish and invertebrates.
“Pacific oysters are potentially acting as ‘ecological traps’ to our native invertebrates by offering suitable habitats, yet harbouring these predators,” Martin says.
The oysters may have other ecological impacts, but this will require more time and monitoring to detect.
Meanwhile, OzFish Adelaide and the Estuary Care Foundation (ECF) are working on restoring native oyster reefs in deeper areas of the Port River and Barker Inlet estuary area, in waters of 6-10 metres depth. Since 2022 more than a tonne of recycled oyster shells has already been placed in the river, with plans to restore a further 5000m2 of locally extinct native oyster reefs.