Harbinger of the Seas

If a nonbasic land has an ability that triggers "when" it enters the battlefield, it will lose that ability before it can trigger.

Harbinger of the Seas doesn't affect names or supertypes. It won't turn any land into a basic land or remove the legendary supertype from a legendary land, and the lands won't be named "Island."

If Harbinger of the Seas loses its abilities, it continues to turn nonbasic lands into Islands. This is because effects that change subtypes are applied before considering effects that remove abilities, regardless of the order in which those effects started.