Huge use of 'Transparent' in GPU profiler for 2D game.

My 2D game runs quite badly. This is on a pretty good PC, not mobile. In the profiler when running a build, I've noticed that the 'Transparent' section is huge, and has even bigger spikes, which I think are the real problem.

In my game I use a lot of transparency. There are lots of objects with overlaying sprites that fade in and out when certain things happen, or just as part of the animation. To do this I've just been using the alpha channel on the sprite renderer (normally through the animator, sometimes through code). I take it this is where I'm going wrong.

So if that's the wrong way of doing it, can someone point me in the direction of the right way.

-Is there a better way of using sprites that need to be transparent?

-What are the spikes about? They don't seem to be related to anything happening in game. If I could just get rid of them I think it would run fine.