If xyz dies then...

[Europhyllia]

I thought this was interesting. Add to the list if you can think of something!

If Xenia dies, expect cyano, because Ping says so.

If certain sponges die, expect diatoms, because some sponges use silica as their building blocks.

[Meslo]

If Killer maroon clown fish kills another fish. She goes to the LFS if she is lucky