Cancerby
sulamkComment: This is going to sound very hard and critical but I hope that you will see my point.
First I recognise this was a hard shot to take - small dark subject - bright background - very harsh sunlight - heavy shadows - angular background - rounded subject and a subject that was either moving or likely to shoot off at any time....Everything was working against you and it would have need a lot of thought to pull it off. What you have ended up with is just a picture of a crab.
If you are on holiday and that is all you wanted then it is fine and pictures like this are great memories but for a competition like this you needed to take some risks.
Some of this will depend how much control you have on your camera - so you may not be able to some of these things. Location may prevent others.
1: Change of viewpoint - get where the crab is facing you - and as close as you can or if thats not possible just shoot half a dozen blind shots - where you have to guess whats in the viewfinder/screen but it looks about right.
2: get down and to the side - with a crabs sideways movement it would appear he was coming towards you and be menacing.
3: Go for the silhouette there may be enough crab out of the shadow for this to have worked.
4: try and get some extra light into the shadow. Almost anything light would have reflected some of that very bright sun into the heavy shadow and lifted the crab out of the blackness.
I always have half a dozen white tissues in my pocket. They can often be used as reflectors if either someone is with you or over the flash to diffuse light when a straight flash would be too hard.
David