In this luminous semi-documentary film that plays on the border of reality and fiction, a young boy from the big city goes on an enchanted expedition to the Banco Chinchorro, the largest coral reef in Mexico. The boy’s wild-man father, who will return him to his Italian mother at the end of the trip, extends a ritualistic passing of knowledge, experience and love from one generation to the next. The characters in Alamar may be playing versions of themselves, but director Pedro González-Rubio has constructed a film in which the journey has an overarching mythic resonance that evokes fables from “Robinson Crusoe” to “The Old Man and the Sea.”