Im a native English speaker and i dont think that ocean and sea are interchangeable at all. There are 5 oceans - I would never call a sea an ocean but if i was up close to it, i might call the ocean the sea. I think this might be a regional thing?
You can't call a sea an ocean but you can call an ocean "the sea", and seaside works for either. https://en.wikipedia.org/wiki/Sea
i live beside the sea.
I am actually living beside the baltic sea today
I live BY the sea. Why is this wrong? Is there a difference between by and beside?
'by the sea' should have worked, we accept it.
Why not "I live at the sea"?
...I live on the coast?
That's definitely not the same.
But living on the coast is living by the sea
OK, my colleagues persuaded me that it makes sense to accept it. Added now :)
Ok could someone please explain why using 'nad' here?
Prepositions often don't have a literal one-to-one relationship between languages. In this case, "nad" + instrumental means a location above the sea. Which, in a sense you are.
It it helps, "Frankfurt an der Oder" translates as "Frankfurt nad Odrą".
Why is seas accepted one time and ocean the next, if they are both viable answers, it's confusing.
I haven't found a sentence accepting 'ocean'... We don't want to accept it, even if some people sometimes use it for 'sea' it's technically (scientifically) a different thing...
..or .. by the sea
Tell me turtle is not mieska, I may be hardof hearing but I'm not deaf.
Turtle is not mieska.
"I live near the sea" was not accepted.
"nad morzem" can have quite a wide meaning, therefore your answer sounds acceptable. Added now.