A rare show at the Mystic Seaport Museum provides a once-in-a-generation opportunity to see British painter J.M.W. Turner’s watercolors. Then, pioneering video and performance artist Joan Jonas on her work and new book, ”I Know Why They Left.” Plus, photographer Jess T. Dugan’s photo exhibit, “To Survive on This Shore,” and the Boettcher Memorial Tropical Conservatory in Denver, Colorado.