Using first-principles calculations, we investigate selected defects in blue phosphorene (BlueP). For a single-vacancy (SV) defect, a 5-9 structure is energetically favorable, and for a double-vacancy defect, a 5-8-5 or 555-777 structure is. A P adatom favors the top adsorption site. Scanning tunneling microscopy images are simulated to aid the experimental identification of the defects. Formation of a Stone-Wales defect is found to be most likely, but it can be reverted by thermal annealing. Calculated migration and transformation barriers show that a SV defect can migrate easily. Both a SV defect and a P adatom induce a magnetic moment, thus turning BlueP into a magnetic semiconductor. It turns out that all of the defects under investigation enhance the ability of BlueP to absorb sunlight.