puddles between the rocks.

A "puddle" is a small pool of water. In this seashore context often they are called "rock pools". Rock pools are often full of small sea creatures. Usually they are clear rather than muddy.

but what I am confused with is that a pool of water should be on the surface of the ground, not inside the sea! In the image, the 3 animals live totally in the water.

See these pictures:

https://www.google.co.uk/search?q=rock+pool&tbm=isch

The pools are replenished each time the tide comes in. When the tide goes out, the water remains in the pools. If a pool ever completely dried out then any sea creatures in it would eventually die, but usually t

When there is a rocky area at the edge of the ocean, at high tide, these rocks are completely underwater, but at low tide, the rocks are exposed, and the depressions between the rocks remain filled with water after the tide goes out. These small water-filled pools between the rocks are usually called "tidal pools," because they only exist when the tide goes out. They are usually not referred to

GPYcalled "rock pools"

Hmmm. I've never heard that term. We call them 'tidal pools' here.

youssefdirWhat's the meaning of puddles? Is it a muddy place down in the sea?

The usual definition of 'puddle' does suggest dirty water, but in this context the water is clean. And it's not in the sea; it's on the edge of the sea, near the shore.

youssefdirAnd do you think the mentioned animals are ok with it?

Yes.

Thank you all. Wonderful information.

GPYI guess you don't live anywhere near the sea?

Actually I do, but I couldn't think of it!

CalifJimHmmm. I've never heard that term.

Then I imagine it is a difference between US English and British English. "rock pool" is the normal term where I live.