Preheat the oven to 375 degrees and lightly grease a 9x9 baking dish.
Cook the fettuccine in a large pot of salted boiling water until al dente, then drain and set aside.
Melt the butter in a large skillet over medium heat. Add the minced garlic and cook for 1 minute until fragrant.
Pour in the heavy cream, then stir in the Parmesan cheese, salt, and black pepper. Simmer for 3 to 4 minutes until the sauce thickens slightly.
Add the shrimp to the sauce and cook for 2 to 3 minutes until they turn pink. Gently fold in the crab meat and remove the skillet from the heat.
Combine the cooked pasta with the seafood Alfredo sauce in the skillet, then transfer everything to the prepared baking dish.
Sprinkle the mozzarella cheese evenly over the top. Bake for 20 minutes until the cheese is melted and bubbly.
Remove from the oven and let rest for 5 minutes before sprinkling with chopped parsley.