Bottom trawling is dramatically altering the ocean floor and harming habitats, similar to the way that farming has permanently changed the landscape, a study said on Wednesday.

Much has been written about trawling's indiscriminate destruction of fish stocks, but a team of marine scientists in Spain, writing in the journal Nature, said some of its practices damaged the fabric of the ecosystem.

Continental slopes, the gradients that connect the shoreline with the ocean floor, are being smoothed out in areas that are intensively bottom-trawled, the team said.

Bottom trawling entails dragging heavy nets and gear along the ocean floor to haul up fish species that feed near the sea bed.

But it leads to vast displacement of sediment and changes to the submarine landscape, the team said.

This disturbs complex ocean floor habitats, "potentially affecting species diversity" in a manner comparable with intensive agriculture, it said.

In the northwestern Mediterranean, where industrialised trawling has been taking place since the mid-1960s, the scientists found the practice displaced 5,400 tonnes of sediment in just 136 days they monitored.

"Trawled continental-slope environments are the underwater equivalent of a gullied hill slope of land, part of which has been transformed into crop fields that are ploughed regularly, thus replacing the natural contour-normal drainage pattern by levelled areas," they wrote.

And while farmers ploughed a few times per year, sea trawling can occur almost daily.

The paper argued that trawling be added to the list of Man's damaging ocean legacies along with such phenomena as sea-level rise and acidification.

Conservationists say a trawling ban will not just conserve fish stocks but give soft corals, sponges and other bottom-dwelling creatures a chance to recover.