OAKLAND -- The A's on Wednesday announced managerial changes at three of their top four minor-league affiliates.

Steve Scarsone will take over at Triple-A Sacramento after spending the past two years at Double-A Midland, Aaron Nieckula was promoted to Midland after managing the Single-A Burlington Bees in 2012 and Ryan Christenson will manage at Single-A Beloit. Webster Garrison returns to manage the Single-A Stockton Ports for the third straight season.

Former Sacramento manager Darren Bush is joining A's manager Bob Melvin's staff as the bullpen coach in 2013. Rick Rodriguez, who was the A's bullpen coach this season, is headed to Sacramento as the pitching coach.

Scott Emerson was named the roving pitching instructor for the minor leagues and Marcus Jensen, the former standout from Skyline High in Oakland, will add the title of roving minor league catching coach in addition to managing the A's affiliated in the Arizona Rookie League.

  • The A's acquired right-hander Sandy Rosario, 27, from the Boston Red Sox on Wednesday for a player to be named or cash considerations. Rosario, spent the 2012 season with the Miami Marlins organization, including four relief appearances with the Marlins before going on the disabled list in June with a strained right quadriceps. He pitched in 10 games for the Marlins over the past three seasons, compiling a 15.26 ERA. He was claimed on waivers by the Red Sox in October.