With resp0ect to the barnacles,
Lepas anatifera is a pelagic barnacle that can be found attached to a variety of floating objects, including driftwood, bottles, boats, buoys, macroalgal rafts, and turtles. It can also be found on fixed objects such as rocks and off-shore structures. This species is most abundant in tropical and subtropical waters where sea temperatures exceed 18-20 ºC.
Range depth: 0 to 2909 m.
Habitat Regions: temperate ; saltwater or marine
Aquatic Biomes: pelagic ; coastal
Other Habitat Features: intertidal or littoral
From Encyclopedia of Life.
Pelagic means open sea. For this species of barnacle to attach itself, as juveniles, to the flaperon, all that would be needed is proximity to a nearby floating object with adult, hermaphroditic barnacles attached.
The route taken by the flaperon was along the northern circulation of the Indian Ocean Gyre, which is a counterclockwise current; a current that conveys all manner of trash and debris.