Step 1

Bring a large pot of heavily salted water to a boil. Meanwhile, set a colander in the sink. Line a baking sheet with a double layer of paper towels.

Step 2

Add 1 pound raw medium shrimp to the boiling water and boil until the shrimp are pink and just cooked through, 1 to 2 minutes for fresh and 2 1/2 to 3 minutes for frozen. Using a slotted spoon, transfer the shrimp to the colander and rinse with cold water until fully cooled. Transfer the shrimp to the paper towels and arrange in a single layer to dry.

Step 3

Bring the water back to a boil over medium-high heat. Add 12 ounces dried pasta and cook according to package directions until just tender, 10 to 13 minutes. Meanwhile, make the dressing.

Step 4

Whisk 2/3 cup mayonnaise, 1/2 cup Greek yogurt, 3 tablespoons finely chopped fresh dill, 1 tablespoon Old Bay seasoning, and 1 tablespoon lemon juice together in a large bowl.

Step 5

If using lump crabmeat, drain 1 pound and pick for shell pieces. If using imitation crab, use your fingers or a knife to break up 12 ounces imitation crab into large, bite-size pieces. Add the crab, 3 finely diced medium celery stalks, and 1 minced medium shallot to the dressing.

Step 6

When the pasta is ready, drain and rinse with cold water to cool. Drain well again. Add the pasta and shrimp to the dressing and toss to coat. Taste and season with kosher salt and black pepper as needed.