What Do Historical Sources Say About the Glowing Ocean Phenomenon?

Noctiluca Scintillans are a microscopic form of ocean life that emit a characteristic blue glow when disturbed either by swimmers or the ocean's natural turbulence (https://www.youtube.com/watch?v=Aaxll8yaAAA video linked here as visual aid). Before the invention of the microscope and the subsequent discovery of these creatures, how did people attempt to explain why the ocean would randomly light up? Did they think it was magic, or a sign from God, or something altogether stranger?