Hey there!

Firstly, I want to talk a bit about your terrain. I think because you've made the majority of your plot out of water, it's not left a decent amount of space for a structure, or a land organic.
However, I think, as this plot is, the terrain works and looks good, if you wanted to add a WATER organic.

Organics are basically living things; an animal, a plant, a person etc.
I think you could really add to this plot by building either a structure or an organic, I'm more leaning to the organic - it's more original. Maybe something like a dolphin, or a whale, or something jumping out of the water :3
Ideas:
http://www.whoa.in/20140224-Whoa/Dolphin-Jumping-Out-of-Water-Wallpaper.jpg
http://www.pageresource.com/wallpapers/wallpaper/dolphin-jumping-high-out-the-water-sundown_355227.jpg
Those pictures just really demonstrate the arch and the curves of both mammals. It also shows the kind of reaction the action has on the water :D
I say this because the plot, as it is, isn't enough to rank. It is good and I like the shipwreck idea, but it's not enough.

I will just add that the tree needs some work. Because you've made the trunk quite tall, the leaves are going to have to be a little larger than they are I think, and wider than 1 block.
http://www.planetminecraft.com/project/stranded-stranger-2858297/ - (Credit: Plutouthere)
Obviously, your tree isn't to the same scale, but use this as maybe a helpful guide to proportions, and the way the leaves sit on a palm tree! :)

Good luck!
- Dutty :3