The third and final film in the Northeastern University Marine Science Center’s 2012 Cinema by the Sea program, “Ocean Frontiers,” is scheduled for 7 p.m. Tuesday at 430 Nahant Road. The film will be followed by a discussion with Winston Vaughn of the Conservation Law Foundation. On its website, ocean-frontiers.org, the film is described as “a documentary and outreach campaign to inspire and mobilize audiences to better care for the ocean, for the good of all.” The event is free and open to the public, and no reservation is required.