It means that maybe you are no longer here and the sea has disappeared, but he still has you in his heart, as if you are by his side.
The story of oysters:
In 1954, biologist F.A. Brown dug up a batch of oysters (Ostrea virginica) from the seaside in Connecticut and put them thousands of miles away An aquarium in a basement in Chicago. He was a biorhythm researcher and knew that oysters responded to the ebb and flow of the tide. During the first two weeks of moving into my new home, nothing changed.
The oysters still live according to their normal rules: sometimes they retract and sometimes open their shells, catching plankton in the seawater to feed themselves, all following the ebb and flow of the distant Conteague coast. Ebb. But over the next two weeks, something inexplicable happened.
They still rise and fall like the tide, but their climax behavior no longer matches that of the Connecticut tide. Not Florida, not California, not Dover, not according to any tide table known to science. After repeated calculations, Brown realized one thing: It was high tide time in Chicago. But there is no sea in Chicago.
These oysters live in reinforced concrete basements in artificial seawater in glass boxes. But they know the existence of the sea, and their ancestors have lived by the sea for hundreds of millions of years; they can leave the sea, but the sea will not leave them. Brown speculated that perhaps the oysters sense changes in air pressure and infer the timing of the tides and their own rhythm.
None of the oysters are doing all this consciously - but in some deep sense, they are imagining such a sea, a sea that does not exist anywhere on the earth. There are ebbs and flows there, and they open and close to the rhythm of the sea. There is no sea in Chicago, but the oysters bring the sea.