Cook the pasta in salted boiling water according to package instructions until al dente, drain and rinse under cold water.

If using fresh shrimp, cook in simmering water until pink and opaque, then chop. If using pre-cooked shrimp, just chop into pieces.

Dice the celery, red bell pepper, and red onion, and place in a large mixing bowl.

Whisk together mayonnaise, sour cream, Dijon mustard, lemon juice, Old Bay seasoning, salt, and pepper in a separate bowl.

Combine the cooled pasta, shrimp, and imitation crab with the chopped vegetables. Add the creamy dressing and toss until well coated.

Cover and chill in the refrigerator for at least 1 hour before serving.