The French 'Marines' unit were simply Sailor batallions (Equipages) without a ship. They acted as line infantry in 1813-14, some handled cannons, and if I'm not mistaken two of them served in Spain as Pontoniers (Bridge-builders) as well.
You must remember of course, that it was not uncommon for French line infantry to act as skirmishers, so it's not unrealistic to think sailors might have found that way as well.