By the sea is "au bord de la mer", "Ã? la mer" in the sense of "seaside".
Ex: I'd like to have a house by the sea: j'aimerais avoir une maison au bord de la mer.
It is "par la mer" when an action is done bythe sea.
Les rochers sont battus par la mer : the rocks are beaten by the sea.
sea vixon
Sea animals are 'les animaux marins' in French.
A sea otter is 'une loutre de mer' in French.
Ocean in French is "Ocean, or you can use Sea in French "Mer". .
sea shells are coquillages in French. For the purpose of a meal, they are called 'fruits de mer' on the menu.
mammifères marins
mer verte
Une hippocampe
monstre marin
A sea nymph is 'une nymphe de l'océan / une nymphe marine' in French.
"a garden by the sea" is "un jardin à la mer / près de la mer" in French.
sirène par la mer