Strain and Trauma are the two different types of damage that Crew Members can suffer. They are tracked on a common track on each Crew Board, and if all damage slots are full, the Crew member dies. The main difference between Strain and Trauma is that different procedures are involved in healing them. Trauma is usually more difficult to heal than Strain.
Some ways of healing Trauma are:
The markers used to track Trauma are red acrylic "gems". They are placed in punched holes on Crew Boards, and put on top of Enemy cards.