After more than five decades serving as a vital artery for the nation’s cargo movement, the Gerald Desmond Bridge has officially started coming down. Crews on Saturday took down the 410-foot center part of the bridge and placed it onto a giant barge in one whole piece. “This moment has been 20 years in the making, from the time we started planning to replace the Gerald Desmond with a taller, wider and safer bridge,” Port Executive Director Mario Cordero said. The Gerald Desmond Bridge, which first opened to traffic in 1968, was named after the late Long Beach city attorney…