Games : Does Gyro Ball get affected by Attack decrease?

I want my Contrary Shuckle to have Shell Smash and Gyro Ball, but inverted Shell Smash would give Shuckle -2Atk, -2SpAtk and -2Spd and +1Def and +1Spdef. But will Gyro Ball's damage be lowered by the -2Atk? I've gone on Battle Spot to test this and Gyro Ball did an extremely bad amount of damage. The speed that my Shuckle is at right now is 15 at level 100.