Hundreds of jobs could be under threat if a lethal parasite attacking Bluff oysters spreads across Foveaux Strait, Invercargill Mayor Tim Shadbolt says.

And the ripple effects would be felt outside Southland.

Dunedin businesses such as Best Cafe and Harbour Fish sold large numbers of the delicacy and were already bracing for the possible fallout.

The warnings came as calls for action mounted following the detection of the Bonamia ostreae parasite at two Stewart Island oyster farms late last month.

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Shadbolt said yesterday that there was real concern the Bluff oyster industry was at risk from the parasite, and losing it would be "absolutely devastating" for the region.

"A lot of jobs are on the line. It would be a tragedy for Southland if this delicacy [disappeared].

"It's just a real nightmare. It's probably the worst issue we've faced since the threat to close the [aluminium] smelter."

The marine parasite was detected in the Marlborough Sounds and Nelson in 2015, but it was the first time it had been found in another part of New Zealand.

It could be fatal to flat oysters, and was believed to spread after oysters died, prompting calls at a public meeting in Bluff on Tuesday for Stewart Island's farmed beds to be pulled up now.

A delegation from Southland also travelled to Wellington yesterday to meet officials and discuss the threat.

Ministry for Primary Industries readiness and response director Geoff Gwyn chaired a meeting of the MPI response governance group yesterday.

MPI had already introduced restrictions on the movement of some shellfish species, farm equipment and vessels to and from affected areas, including Stewart Island, to limit the parasite's spread.

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Beyond that, lifting the Stewart Island farmed oyster beds was "one obvious option" to protect Bluff's wild oysters,"but there are others", Mr Gwyn said.

He stressed the need to avoid a "knee-jerk decision".

John Edminstin, an oysterman and chairman of the Bluff Oyster & Food Festival, said the "best course of action" would be to lift the Stewart Island beds before the parasite reached Bluff's wild beds.

Not everyone agreed with that idea, but there was little choice - and little time, he said.

Shadbolt said he had been told at least 400 workers worked in jobs connected to the oyster industry, and would be affected if the parasite spread.

Best Cafe co-owner Brent Charnley said the threat was also "worrying" in Dunedin.

"Oysters to us are a big part of our business ..."

He was watching developments, as was Harbour Fish owner and manager Aaron Cooper.

"We would be concerned." Otago Daily Times