1. In a 5- to 6- quart pan over high heat, stir onions and celery in butter until limp, about 5 minutes. Add tomato paste and curry powder, and stir 1 minute longer.
2. Add squash, apples, broth, 4 cups water, ginger, bay leaf, cloves, and pepper. Stirring often, bring to a boil; cover, reduce heat, and simmer, stirring occasionally, until squash mashes easily, 30 to 40 minutes.
3. Remove and discard bay leaf and cloves. In a blender or food processor, whirl squash mixture, a portion at a time, until smooth.
4. Pour purée through a fine strainer back into pan. Add sherry and stir over medium heat until just steaming, about 2 minutes.
5. Meanwhile, remove any bits of shell from crab.
6. Ladle soup into wide bowls. Mound equal portions of crab in the center of each bowl. Garnish with bell pepper, if desired. Add salt to taste.