The coast, the frontier between land and sea, gets it's countless shapes from the breath of the tides. Twice a day the tide rises for six hours, followed by six hours of descent . Every day the amplitude and the rhythm change between high and low tide according to the lunar cycle. The strong tides coincide with the full moon and the new moon, the weak tides with the first and last quarters.

The rocky shore uncovered at low tide and well known by fishing enthusiasts on foot, conceals under each pebble a whole animal world : a carpet of shells and crustaceans living in the cool shade of the tide pools. On the coast around the estuary, enormous mud flats appear at low tide providing the herring, black-backed and black-headed gulls, oyster catchers and kilder birds with the riches of a never-ending food supply. From tide to tide, the interchange between the ocean and the coast continues, undermining the cliffs, filling in the bays.