I actually don't get to see very much of the places I travel to. Very often, I'm immersed on the logistics and production of bringing a project to life and so it's much more head down in the ground to "survive the project" more than anything else!
To answer your question though, I think that the most fragile ecosystems are the ones that happen far beyond what we see. Insects for example are dying at an alarming rate, along with coral reefs - both fairly out of sight, out of mind.
The problem I think with photographs of pristine beautiful landscapes and ecosystems that you see on Instagram is that they provide us with a false sense of security and stability.
Sorry that was a little depressing, but the numbers don't lie.