Mud has a quality unique on Earth : in mud are concentrated all the building blocks necessary for the construction of life ; in mud, the link between the infinitely large and the infinitely small is made possible.

Daniel Guiral, aquatic ecology specialist, takes us to the Kaw River estuary, near the border between Brazil and French Guyana, and in the immediate vicinity of an immense mud bank.

This region is like an open laboratory enabling us to observe the behaviour of the mud's strange and fragile inhabitants.

It is in this hostile yet vastly rich environment that the scientist reveals to us one by one the links of the biological chain and makes new discoveries, in particular concerning the micro-organisms living in the mud and the reproductive method of the only tree in the world capable of developing in saltwater : the mangrove.