A traditional fiddler crab breaks out of his shell and goes beyond the call of duty to dive into a global climate crisis to save his sister, their slice of the creek, and potentially the world.

I quite liked this logline. There is a cartoony nature about it. The use of "breaks out of his shell" offers the double meaning (figurative and literal) hinting to me that this will be a fun read and won't take itself too seriously. Expecting some comedy moments.
The end sets up the stakes (climate crisis), the world (the creek), and the scope of the story (the world).
I'd want to read this script (or watch the movie).

There are a lot of words in this logline that don't really tell us anything about the plot or what this story is actually about.

Because when you tell us the lead must break out of his shell and go beyond the call of duty... it is like a coach telling reporters the team needs to give 110%, instead of saying, we need to work on the offensive line and get the running game going.

In order to improve the logline, you should start with what specifically happened to the fiddler crab's sister. Because what happens to her seems to be what sets the story in motion.

Without knowing what the lead character's sister needs saving from, makes it difficult to picture the story in our heads.

Then, after you tell us specifically what happened to the lead's sister, you should tell us what the lead character plans on doing about it. The lead carrying out the plan will be the plot. So telling us the plan will help us visualize the story.

Also by the end of the logline, we should at lead have an idea of what is standing in the lead characters way as well.

Anyway, you obviously have an idea in your head, hope this helped give you an idea on how to put that idea into logline form.