Cook pasta in a large pot of boiling salted water until al dente, about 8-10 minutes. Drain and rinse under cold water.

Sauté fresh shrimp in a skillet over medium heat until pink and opaque, about 2-3 minutes. Chop if necessary.

Finely dice celery, bell pepper, and red onion. Chop parsley for garnish.

In a mixing bowl, combine mayonnaise, sour cream, Dijon mustard, lemon juice, Old Bay seasoning, salt, and pepper. Whisk until smooth.

In a large serving bowl, combine cooled pasta, shrimp, imitation crab, and chopped vegetables. Pour the dressing over and toss gently.

Cover and refrigerate for at least 1 hour to chill and allow flavors to meld. Garnish with parsley before serving.