Tidepool Tim says, "Sea grapes are pretty boring, really.  Not much to say about them except for the fact that they're another species of tunicates that we have here in our cold Atlantic waters.  They are common on EVERYTHING that is floating out here in our bay from channel markers to lobster buoys, to mooring lines.  They literally COVER the nets used in our local salmon aquaculture farms.  Sometimes there are so many sea grapes growing on a net that massive cranes must be brought in just to change the nets out on the salmon cages. 

In our tidepooling quests we often see them cemented to the bottoms of rocks that have good water flow under them.  They do look like a peeled grape or a jelly-bean that some kid sucked the outside off and pitched into the sea.  Looking closely, one can see the siphons and the primitive guts through their tunic or skin.  There are a bunch of different species around - we call them all 'grapes'. Often they are mixed in with several other species of squirts on a rocky bottom and also beside lamp shell."