Small organisms are struggling to survive as the ocean becomes more acidic, researchers say, including tiny sea snails whose shells are dissolving.

Key points: Acidification could severely affect the ocean's food chain

Acidification could severely affect the ocean's food chain Small organisms are being damaged and scientists fear it could affect large animals

Small organisms are being damaged and scientists fear it could affect large animals A prominent researcher says reducing CO2 emissions would reduce acidification

Researchers fear an increase in acidification in the Southern Ocean could have a severe impact on the food chain off Australia's south coast.

The concerns come as 350 scientists from more than 30 countries gather in Hobart for an international symposium on the impact of carbon dioxide on the world's oceans.

Ocean acidification means the pH level of water has decreased, making it inhospitable for small organisms.

CSIRO research scientist Andrew Lenton was part of a team that developed a map of acidification around Australia.

He said the impact was already being felt.

"The changes in Australia are very close to the changes that are occurring everywhere else in the world, so this is really a global problem that Australia is part of," he said.

"Already there are detectable changes in the Southern Ocean."

Reducing carbon dioxide emissions would reduce acidification

Mr Lenton said some organisms had been affected more than others.

"There are changes in the shell weights of some of the organisms," he said.

Tiny free-swimming snails called pteropods are a vital part of the food chain. ( Supplied: NOAA )

"We're seeing the bottom or the lower parts of the ecosystem being impacted already, we want to know how does it impact all the way through the ecosystem?

"What does it ultimately mean for the large predators as well?"

The impact is also visible in tiny free-swimming sea snails call pteropods, which are a vital part of the diet of many large fish.

Researchers said the percentage of pteropods with dissolving shells observed had doubled since the pre-industrial era and was on track to triple by 2050.

Dr Richard Feely from the US National Oceanic and Atmospheric Administration (NOAA) said reducing carbon dioxide emissions was the best way to avoid acidification.

"In order for us to address ocean acidification on a global scale we would have to add two billion tonnes of calcium carbonate," he said.

"That is two billion Volkswagen Beetles into the water every year every single year in order to address ocean acidification.

"It's just economically not feasible to do that so this is why we're saying the most important thing we can do is reduce CO2 emissions right now and make sure [more acidification] doesn't happen."