A retreat for nuns that has withstood six hurricanes and three nor’easters also dodged its most recent demolition bullet when it was purchased by a nonprofit that hopes to uses it to fuel scientific study in the ecologically rich area. St. Mary By-the-Sea — the red-roofed former hotel located yards from where the Atlantic Ocean meets the Delaware Bay in Cape May Point — was officially sold to Cape May Point Science Center, LLC for $5.5 million by the Sisters of St. Joseph, a Catholic order of women who practice educational, social services and parish ministries. The Sisters had owned the 1.5 a…