Matango (1963), directed by IshirÅ Honda.
Aka Attack of the Mushroom People (which gives it away).
When a disparate group on a pleasure cruise encounter a sudden storm, their yacht is disabled and they drift for days into strange, fog-bound southern latitudes. After an encounter with a mysterious ghost ship (was it a dream?) they make landfall on a deserted (?) island. The rotted hulk of a research vessel is encrusted with lurid fungus and -- oddly enough -- all the mirrors have been removed... We all hope they don't eat those mushrooms.
And the movie still has an hour left!
It's pretty downbeat. Even apart from the sinister fungoid horror the group has no cohesion and their survival story is grim.
It is a compelling presentation of the desire to submit that is so important in this type of film, to cross over and accept your awful fate. Maybe it won't be so bad once you've been bitten by the vampire and are damned and immortal, or have become a ravening werewolf unbound by any constraints. Even zombies are worry-free and have plenty of company.
This time the motivating excuse is hunger, which everyone can understand. Either starve or eat the mushrooms and become fungoid horror. Everyone else is doing it.
Director Honda and the cast and crew mostly did giant monster films, although we last saw Yoshio Tsuchiya as the fierce farmer Rikichi in The Seven Samurai (1954).
As a further oddity this is based on a short story by little-known English author William Hope Hodgson, who died in the trenches during WW1. His weird books The House on the Borderland and the epic The Night Land are flawed but intensely interesting. I think all Sargasso Sea plots come from his work.
Available on an early anamorphic DVD with just fair image quality. It has both the original Japanese audio, English dub tracks (both mono and 5.1), subtitles, and a Japanese commentary track with English subtitles.
The aspect ratio is 2.55:1.