Maritime science fiction is a subgenre of science fiction that takes place in the ocean or the sea and commonly has sea monsters and/or maritime technology.
One such example would be the American TV Series “seaQuest DSV”. The series follows the adventures of the high-tech submarine seaQuest DSV (Deep Submergence Vehicle) whose job it is to protect the last of the resources on earth from non-aligned nations as well as aid in mediating disputes, research, and explore.
There are various science fiction works, such as Star Trek, which do not take place at sea but in a comparable setting, such as space; where the threat and theme of the dangers of the unknown (e.g.: Sea/space Monsters) is still present.
Although not primarily a maritime science fiction itself, the Star Wars universe includes elements of maritime science fiction such as the underwater city of Jar Jar Binks in Star Wars: Episode I – The Phantom Menace.