Maybe you haven’t heard of the Ross Sea but after watching this film, you won’t forget it. Located in the Southern Ocean, it’s home to an abundant array of aquatic life, including whales, penguins and seals, and is the last pristine marine ecosystem on earth. No surprise, this special body of water is under threat from commercial fishing. The population of Antarctic toothfish — a particularly unattractive animal that was renamed Chilean sea bass for menus — has diminished severely, and other species may follow. The Last Ocean, directed by Peter Young and featuring photography by John Weller (whose images are at Arroyo), is clear about its intent: This body of water is more valuable as an ecosystem than as a fishery, and the way to keep it intact is by pressuring the government of New Zealand.