Edited and introduced by Gwynne Vevers
The aqualung diving technique has opened up for the marine biologist the relatively unexplored sea bed from below tide and down to about thirty fathoms.
HANS HASS recalls a recent expedition to the Maldive coral reefs in the Indian Ocean and tells of the dangers and delights of free-diving.
RICHARD BAIRD explains his underwater studies on the escallop beds of the North Wales coast.
ROBERT FORSTER , from the sea bed off Plymouth, talks with Gwynne Vevers , in a boat above, about the animals and seaweeds on the sea bottom.
Produced by Jeffery Boswall