The land-sea interface is out of balance due to extreme natural phenomena and strong anthropic pressure. The development of human activities in this area generates a growing return effect from the sea to the land. Controlling this complex and constantly changing dynamic remains a fundamental challenge.

All over the planet, the ocean is suffering, that is a fact. Scientists now concur on the anthropic origin of this massive imbalance. Beyond those natural phenomena discussed in the previous section, human activities directly contribute to this condition.

The complex Ocean Sphere* system does not end at just a short distance from the coast, but rather at the border between the ‘’Shoreface’’*, i.e. the immediate part of the platform, and the intertidal zone*. In the same way it interfaces with the atmosphere, shaping our climate, it also interfaces with land, influencing it considerably, at the coastline.

In turn, human activities carried out in this space also impact the ocean and the sea, the oceanic expanse bordering the shoreline, in particular. There is thereby a dual pattern of influence: from sea to land (ecosystem functions, marine meteorological phenomena, …) and from land to sea (human activity).

Understanding the structural and cyclical nature of this interface (Chapter 1) helps us anticipate the twofold alteration to come: that of the ocean and that of human activity and habitats.

Indeed, a complex interaction is played out on the coastline:

• between two distinct natural components: the Ocean Sphere on the one hand and the rest of the planet on the other (lithosphere*, biosphere*, hydro and cryosphere*
  and atmosphere*);
• between the natural environment and human civilization, with its ambivalent attraction,
• between the diverse components of humanity: ocean-’’junction’’ ocean-border, relational space as much geopolitical as economic.
  The survival of the ocean, and hence that of the human species on this planet, depends on the capacity of human beings to anticipate changes to this interface and resolve the issues that come with it (Chapter 2).