In ominously cloudy water and among half-seen shapes the Xarifa scientists continue their work underwater in the Indian Ocean, studying the power of certain sea anemones to recognise the exact species of clown fish living among their tentacles, while attacking and killing others. Finally, another remarkable relationship is discovered-between sand-living sea-urchins and the shoals of little fish that shelter in their spines.
Directed and produced by Hans Hass in association with the BBC Natural History Unit