You can turn ordinary mangrowe plants in to bonsai, they'l fit perfectly. You can force them to grow elaborate and wisually interestin root system by growing them in just water for the forst year. Choose smallest propagules you can find. Sand wont stay like that unless contained in some way, so an iland in a middle made from some sort of a container would work better long term than a pial in a corner. Alternativey, you may choose to containe water insed of sand. You also can simulate the tidal action if anothe water container (sump of a sorts) is included with a pump on a timer. If u have an exess to such an environment, i am sure u can find tons if little bisties to make this an exqisitly interestin terrarium, but, unfortunately, few of these are commercially available. Good luck!
