Regarding ships
It's highly unlikely that the watch on a bridge will be looking out for falling aircraft; their view of the sky - from inside - is practically nil.
Having said that you can be pretty certain that all ships in the possible vicinity were alerted quickly and that at the very least their courses would be altered to cross the possible wreckage path. Ships traveling between East Coast South America and Europe are pretty much under the flight path and I would guess that at least twenty commercial vessels right now will have all the crew that's awake on a sharp lookout.
By the way Automatic Vessel Identification System or AIS only works in vhf range.