Prick the duck skin all over with a fork. Mix the marinade tucupi, garlic, lime juice and salt and pour it over the duck. Refrigerate for at least 2 hours, or overnight.
Heat the oven to 400°F (200°C). Lift the duck from the marinade, reserving the liquid, and roast skin-side up on a rack for 45 to 50 minutes, until golden and much of the fat has rendered out.
Meanwhile, bring the broth tucupi, the reserved marinade, culantro and peppers to a boil in a large pot. Lower the heat and simmer for 20 minutes.
Add the roasted duck pieces to the tucupi and simmer gently, partly covered, for 45 minutes to 1 hour, until the meat is very tender.
Blanch the jambu in boiling salted water for 2 to 3 minutes and drain.
Arrange the duck in a deep platter, lay the jambu around it and ladle the hot tucupi broth over everything. Serve in shallow bowls.