Quagga Mussel question

My local lake (Piru) just announced they officially have the Quagga mussel. I have done a lot of research regarding the mussels and know how to decontaminate the boat/ballast, but a question came up about the water in the engine block. The ranger said to fire up the boat dry for a second to flush the water out. This does not sound too great for the impeller. We only go to Piru and Colorado River (both have mussels now).

Question: Is there any concern about the mussels clogging up or messing up the engine if we do not flush it out after each use? How long can the mussels stay alive in the water in the engine? Any help would be greatly appreciated.