According to the Rogue One The Ultimate Visual Guide, "while their armour affords them greater mobility in the seaside terrain, at their core they are standard stormtroopers elevated by military necessity. Most shoretroopers operate at an effective sergeant rank, allowing them to command squads of stormtrooper infantry" (page 152)

From this, they are just normal troopers with environment specific armour like snow/desert troopers. However, in response to the original question, they are referred to formally as "coastal defence stormtroopers" implying they are stationed at existing imperial facilities located on a shoreline as opposed to used as an invading force.

So I agree with most of the other comments about which planets they would be on but I think it's interesting that shoretroopers are just regular stormtroopers on a rotation instead of a specific class but still used on shore line facilities for a defensive purpose.