MacPort : Is a given package a dependecy for another one ? My MacPort package are becoming the huge mess. I probably won't use some of them and I was wondering how I could know if a given package is a dependecy for another one. 

For example I have GTK3 installed. How could I know which other installed package needs GTK3.
From Macports guide You can list all the ports dependent on a port x say

port echo depends:x


To find ports that have no dependants use 

port echo leaves