This is the clarification that Francesco Marcheselli sent me about this:
As a note to "Canção do mar" you say: "It seems Amália Rodigues sang this song..."
In actual fact Amália never sang "Canção do mar" as such: the song came from the repertory of her contemporary and friend/rival Márcia Condessa, who proposed it to Amália, judging it was more suitable to her. The song was to be included in the soundtrack of the French production "Les amants du Tage" ("Os amantes do Tejo" - 1955), but the text of the song was found not to be in line with the plot of the movie... As a result an alternative text was written and the song became, in Amália's interpretation, "Solidáo".
It is only fair to remind you that it was "Solidão" who (along with "Barco Negro", from the same movie) became enormously famous, while the "Canção do mar" version remained little known, until Dulce Pontes brought it to light again, as you correctly recall, with her 1995 Coliseum concert, as the preceding recording had gone largely unnoticed.