This is a setting prompt.

Quite simply, I'd like you to set a story in the ocean. But not the top bit, near the sky - the darker waters below, where daylight is scarce. Some really interesting creatures live there, and I challenge you to explore them.

There may be a bit of research required. Or you can make up your own ocean-dweller! There is artistic licence here. 

I'm really interested in what you will create for this! Do send in your stories.

Enjoy writing!