Creatures which are "very important" for local fisheries could be disturbed if plans to excavate an area of seabed go ahead, a marine expert says.
Dr Steve Widdicombe told BBC Inside Out that worms and small crustaceans were living in the sand.
Marine Minerals Ltd (MML) wants to sift the seabed for tin at least 200m from the low water mark off the coast at St Ives Bay, Porthtowan and Perran.
It said a "very high" percentage of life in the seabed would survive.
MML is producing an environmental assessment of the area before making an extraction licence application to the Marine Management Organisation (MMO).
It called the area a "relatively barren area of sand".
Dr Widdicombe of Plymouth Marine Laboratory, analysed a sample of the seabed from the area which could be excavated.
He said animals found in the sand were food for sea life, the basis of the fishing industry in the area.
He said: "Just because it seems there's no life in here doesn't mean there isn't.
"All these animals live within the sand grains looking for other material.
"You need to think about this sediment as a microbial generator of nutrients which is very important for coastal zones in being able to fuel the huge amount of productivity we have in the fisheries."
MML said if it got permission, it would be scooping up sand from the seabed using a crawler-based vehicle for sifting on a boat before replacing the sand on the seabed.
Director Mike Proudfoot said: "We are doing parallel trenches leaving blank areas in between to allow the seabed to recover by migration of species.
"We can't say 100% will survive but it will be very high according to our scientific advisors."
MML is aiming to extract tin from the sands which are rich in waste, or "tailings", from the old mines around Cornwall which washed down rivers and streams into the sea.
During the 18th and 19th Centuries, Cornwall was one of the most important and influential metal mining regions in the world.
It believes that about 40% of the tin mined on land is now sitting on the seabed.
MML said it expects to make its application to the MMO by early next year. After that, the plans will go through a public consultation before the MMO makes a decision.
Inside Out is broadcast on BBC One South West on Monday, 28 October at 19:30 GMT.