Antonyms:
* Terrestrial: Relating to the land or its inhabitants.
* Freshwater: Relating to water that is not salty, such as lakes and rivers.
* Aerial: Relating to the air or atmosphere.
Synonyms:
* Aquatic: Living or growing in water.
* Oceanic: Relating to the ocean.
* Nautical: Relating to ships or sailing.
* Seafaring: Relating to sea travel.
The best antonym or synonym will depend on the specific context in which you are using the word "marine."