SYDNEY, July 31 (Xinhua) -- Sharp declines in humpback whale sightings and an unusual influx of rare seabirds off Australia's east coast have raised concerns among scientists that marine heatwaves may be disrupting ecosystems in the Southern Ocean.

In late June, whale watchers in southwest Western Australia state reported humpback whale numbers about 60 percent below normal during the species' annual migration from the Southern Ocean to feeding and breeding grounds, according to an article published on The Conversation website on Friday.

A week later, birdwatchers observed unusually large numbers of rarely seen albatrosses and petrels off Australia's east coast, far from their usual foraging grounds deep in the Southern Ocean, with many birds in poor condition, the article said.

"If these species are changing their behavior, it could be a sign of altered conditions in the Southern Ocean," wrote Mary-Anne Lea, adjunct senior research fellow at the University of Tasmania, and Christopher Chapman, senior lecturer at the University of New South Wales in Australia.

Researchers said a persistent marine heatwave has affected waters around Australia's Heard and McDonald Islands, a biodiversity-rich region increasingly threatened by climate change, since February, while the southern Tasman Sea has experienced similar conditions since at least April.

They said it remains unclear whether the sightings were linked to the marine heatwave, but such events can alter ocean currents, weather conditions and prey availability, potentially affecting the movements and feeding of whales, seabirds and other marine predators.

The authors said long-term monitoring of key species, environmental conditions and food sources is needed to better understand ecosystem changes in the Southern Ocean.