My suggestions would be:
- Build a generous number of Urchins as backup.
- Spread out your Sirens/Claymores so that when the Scallop ball is lobbed at you they catch as few of your units as possible.
- When practical, keep a few Envoys far enough back that when the ball is lobbed at you, they can't stay on the surface forever without taking substantial artillery fire.
- In the long run a Likho or Reef missile can put a pretty big dent in a dense Scallop ball.
That being said, these are mostly defensive options. I'm not happy with how hard it is to go on the offensive against the Scallop/Lobster ball.