First, bring a large pot of salted water to a boil. Add the pasta and cook according to package instructions until al dente. Drain and rinse under cold water to stop the cooking process, then set aside to cool.

Meanwhile, prepare the dressing. In a small bowl, whisk together the mayonnaise, sour cream, lemon juice, Old Bay seasoning, salt, and pepper until smooth and creamy. Set the dressing aside.

In a large mixing bowl, combine the cooled pasta, chopped imitation crab, cooked shrimp, diced celery, diced red onion, and thawed peas. Gently toss to combine all the ingredients evenly.

Pour the dressing over the salad and mix well to coat everything thoroughly. Taste and adjust seasoning if necessary. Cover the bowl with plastic wrap and refrigerate for at least one hour before serving to allow the flavors to meld.

Before serving, garnish with fresh parsley if desired, and give the salad a gentle toss to refresh it.