1. In a large soup pot, heat the olive oil. Add the onion, celery, half of the carrots, the smashed garlic cloves and the reserved lobster shells. Cook over moderate heat, stirring, until the vegetables are softened slightly, about 7 minutes. Add the wine and cook until nearly evaporated, about 5 minutes. Add the thyme, bay leaf, peppercorns, coriander seeds, fennel seeds and 2 quarts of water and bring to a boil. Simmer over moderate heat until the liquid is reduced to about 6 cups, about 45 minutes. Strain the broth into a heatproof bowl and discard the solids. Rinse out the pot.
2. Return the broth to the pot. Add the potatoes, fennel, saffron, orange zest, tomatoes, minced garlic and the remaining carrots; bring to a boil. Season with salt and pepper and simmer over moderate heat until the vegetables are tender, about 20 minutes.
3. Add the mussels to the pot, cover and cook until they open, about 3 minutes. Gently stir in the halibut and lobster meat and cook until the halibut is white throughout, about 2 minutes. Serve in deep bowls, sprinkled with the parsley.
SERVE WITH Mayonnaise seasoned with minced garlic, saffron and cayenne pepper on toasted baguette slices.