India, Dec. 10 -- The Thames estuary in southeast England - the tidal stretch of the river - once supported extensive saltmarshes, seagrass meadows and oyster beds. These shallow areas, which flood and drain with the tides, provided vital feeding and nursery grounds for fish. But centuries of urban development have replaced them with concrete walls, docks and flood defences.

Much of this change happened in the Victorian era. The Thames embankment straightened and hardened the river's edge, severing the natural connection between land and water. Today, barely one per cent of those original intertidal habitats - the shallow zones between the low and high tide mark - remain. But while the physical landscape has continued to shrink, the cond...