South Australia’s world-renowned giant cuttlefish mating season has recorded its lowest turnout on record, with government surveys counting just 1,811 cephalopods along the Cuttlefish Coast this year compared to 63,000 last year—a 97% decline linked to a protracted toxic algal bloom.
Every winter, a sliver of the South Australian coast hosts the world’s largest mating event for giant cuttlefish. The unique marine species, endemic to southern Australia, traditionally draws hundreds of thousands of animals to the shallow waters of Point Lowly, northeast of Whyalla, where they put on colorful, shape-shifting displays that attract thousands of enthusiastic divers and marine fans from around the world.
A Record Low and a 97% Population Drop
Official figures released by the state government estimate that just 1,811 cuttlefish arrived to breed during the most recent mating window. That figure represents a severe drop from the 63,000 animals recorded during the previous season, and a dramatic collapse compared to historical gatherings where more than 100,000 cephalopods converged along the rocky reefs. During May and June, tourism operators reported seeing fewer than 10 cuttlefish per dive in areas where they would typically see 100 or more animals.
While cuttlefish populations have experienced natural fluctuations in the past—dipping to a record low in 2013, though still numbering in the thousands—observers point out that this year’s numbers are unprecedented. Because giant cuttlefish have a life cycle that lasts about a year and adult animals typically die after breeding, the survival of the next generation depends on the mating success of the previous year.
The Algal Bloom Threat and Ecosystem Impact
State environmental authorities point to a toxic algal bloom that has ravaged the state’s coastline for more than 18 months as a possible cause behind the decline. The bloom has been dominated by the microalgal species Karenia cristata, which can have a significant and swift impact on cephalopod populations.
Researchers investigating the collapse note that cuttlefish may have experienced direct exposure to the toxic waters, or alternatively, suffered from a depleted food supply. As obligate carnivores, giant cuttlefish hunt live prey such as crabs, shrimp, small fish, molluscs, and worms using their tentacles. A broad disruption to the marine food web in their shallow nursery grounds creates immediate survival hurdles for a population already isolated to a specific eight-kilometer stretch of coastline.
Scouring the Coastline for Remaining Eggs
Alarmed by the low adult turnout, the South Australia Department of Environment and Water deployed field teams to assess the reproductive output for the upcoming year. Manny Katz, 28, was one of four divers tasked with surveying the Cuttlefish Coast to count surviving eggs along the rocky reefs.
Over two days in July, the team completed eight one-hour dives, meticulously exploring the undersides of rocky reefs and seagrass meadows where females normally deposit millions of eggs to shelter them from tides and currents.
What Lies Ahead for the Cuttlefish Coast
The drop in both breeding adults and surviving eggs has prompted calls for the species to be listed as endangered. While the National Heritage-listed aggregation faces severe headwinds, marine biologists note that cephalopods possess a natural capacity for rapid growth and quick reproduction if environmental stressors lift.
Whether the unique Point Lowly population can bounce back from the toxic event depends heavily on water conditions, food abundance, and predator presence in the coming months. For now, scientists continue to monitor the coast, searching for answers to a silent season that has left one of marine biology’s most unique spectacles fighting for survival.
