ST. PETERSBURG — Jennifer Hardin, the longtime chief curator at the Museum of Fine Arts, St. Petersburg, resigned Friday. The announcement, sent Friday via email to the museum's board of trustees, was unexpected. "I think the world of Jennifer," said Kent Lydecker, the museum's director. "I can't give you any specific reason. I sincerely regret her decision.""I have immensely enjoyed my work at the museum," Hardin said. "I don't have any plans right now." The museum, which opened in 1965 on St. Petersburg's downtown waterfront, is an encyclopedic institution, meaning that its collection covers the full range of human history. Hardin, 51, became its curator in 1995 while she was finishing her doctoral degree at Princeton University. At that time the museum's collection numbered 3,700 works. During her tenure, it has grown to more than 20,000. Being a curator means both being responsible for the care of art and for "presenting and explaining art," as Lydecker said, mainly through exhibitions. Curators must have deep academic knowledge as well as a feel for how art should be displayed. Hardin has curated many exhibitions originating at the museum. "Monet's London: Reflections on the Thames" in 2005 was the most ambitious, she said, with 150 works lent from 30 venues in Europe and the United States. But she is also especially proud of a Georgia O'Keeffe show in the late 1990s, "done on a shoestring," and another featuring folk art in 2007 when some scholars were dismissive of it "and now the Met (Metropolitan Museum of Art) is collecting it." In 2012, philanthropists Bill and Hazel Hough gave $2 million for a new curatorial position and wanted Hardin's position to be renamed the William and Hazel Hough chief curator. She leaves on June 26 "because I want to finish up the photography exhibition. It has 175 objects and is the largest one we've ever done from our photography collection." That show, "Five decades of Photography at the MFA," opens June 20 after "Monet to Matisse: On the French Coast" departs on May 31. She said she'll relax at the home she shares in the Driftwood neighborhood with her husband, Emmanuel Roux, who for years co-owned the popular Garden restaurant. Lydecker plans an immediate search for a curator who will "build on her record of achievement." "It's been a privilege to participate in so many projects," Hardin said. "But I have been really thinking on a personal level about what would make me happy."Contact Lennie Bennett at [email protected] or (727) 893-8293.