You could turn on snapping, set your edit task to autocomplete polygons, select all of your polygons and then use the trace tool to go around the mass, switching to the regular sketch tool to jump across the gaps with snapping, and then finish. You may have to go back to delete some pockets that you don't want filled. Or you can manually use the sketch tool to jump across each end gaps and fill it in, with those that are open at two ends requiring you to plug in one end first.