Well, here's a pretty scene, the underwater creatures and the tall lighthouse joined by a seagull and a cloud in the sky.
There are black markings all the way up the lighthouse and on the support for the lighthouse going down to the sea bed. These markings are $1$ metre apart. I have left the numbering for you to do.
The sea level is of course "$0$" and then positive numbers going up and negative numbers going down to the sea bed.
If we think about the mouths of the creatures then we can see how much deeper they are from each other, or what distance they are apart.
For example the (mouth of) the fierce looking blue and white fish near the middle is $1$ metre deeper than the (mouth of) the golden yellow fish.
It would be interesting to know how you arrived at your answers.