A Gladstone-based ecology expert says she is concerned two species of seagrass in the central Queensland city's harbour may now be extinct.

CQUniversity professor Marnie Campbell says the two species are a vital food and habitat resource for native dugongs and turtles.

Professor Campbell says current surveying methods cannot adequately track rare types of seagrass.

She says she is proposing a new study that would make up the shortfall.

"We've looked at records of the seagrass distribution, then gone and checked all those sites and we just couldn't find it," she said.

"So we definitely know when we've been out at these sites that those species were not there.

"What we've tried to do is get some more funding so we can actually go out and do a more comprehensive survey of the harbour to find them."

However, James Cook University seagrass expert Michael Rasheed disagrees.

Dr Rasheed sits on the Dredge Technical Reference Panel, which provides advice to the Gladstone Ports Corporation through its massive dredging program.

He says the hypothesis does not match their data.

"I think that the two seagrass species that they named, certainly with halophila spinulosa I don't think there's much danger of it becoming extinct," he said.