Great picture as it is,
but if you want stars below, there are several ways to do that.
I think warer transparency doesn´t play a role in this image, so you could replace the water shader with a reflective shader.
But maybe your water is simply to rough to reflect stars?
You can always mix any image map, shader or watever through a merge shader (using for exaple a distance shader for control)
But I really like it as ist is.
Best Regards,
Jan