Problem with Composting 4 Render Layer with alpha over nod

Hi all,
i have underwater Szene with 4 Layers:

  1. Szene: World Volume
  2. Lights:
  3. a Watch
  4. a Fisch: simulate the red cube

i want that the World Volume Szene are unsharp (Blur)
the Lights are with fog glow
the watch nothing filter, only sharp
the fisch behind the watch little unsharp (blur)

But i can not organize the Render Layers correctly.

Here are the Blend File with the Problem:

i think it is easy but i have no experience with different render layers

kind regards Horst