Good start, few things you could think about adding:
Sea moss around the dock parts, cracks in the shore-wall/waterlines with small crustations growing.
As for the cobble stone:
http://www.blwg.nl/mossen/korstmosse...r/sea_dyke.jpg
Think about a dyke maybe..
If you're doing dock yards then fencing like here:
http://www.tampabaydocksforrent.com/...ck_harbour.jpg
Hope this helps you out a bit..