The Miami-based developer Related Group has begun construction on the Manor at Harbor Island in downtown Tampa. The 21 story apartment tower will house 340 units at 402 Knights Run Ave. The company paid $12 million for the 1.27-acre site in February and received $60 million in financing from Bank of America. Related also hopes to begin work soon on a second project in the downtown district after the purchase of the Tampa Tribune’s downtown offices this past summer.