Wonderful ecosystem, but considering your focus, you could have done something a little more with the gastrodon. I mean, sure they aren't very noticeable or particularly pretty looking creatures, but it needs a little more spotlight. On the other hand, the interaction is done wonderfully, with in my opinion (though to be honest, I am an amateur in both Pokemon and real life) balance and realism... or at least as realistic as Pokemon can get.
Strangely enough, when I first looked at the picture, I had no idea they were actually Pokemon. It was only after I paid closer attention to your Starmie that I realised something was off. I felt like such a dufus.