It reduced the no# of brood produce I'm fairly certain.
I've had them in both non cO2 and CO2 enriched tanks. They will breed like flies in either tank, but you will get higher production without CO2. This was even more the case with CRS.
Definitely effects breeding, as Tom said, the more co2, the less babies. I'm not sure whether it is from carbonic acid eating their shell or just making it hard for their blood to expel co2, but it definitely effects the amount of babies that survive.