In a small saucepan, combine shaved fennel, onion, sugar and marmalade and cook for 10 minutes over medium-low heat. Set aside to cool to room temperature
Preheat oven to 375 degrees F. Combine onion, lime zest and juice, mustard and mayonnaise in a bowl, and then fold crabmeat into the mixture so that it's just combined and the crab is not broken or mashed. Season with salt and pepper, as needed. Arrange bread on a baking sheet. Using a melon baller, or small scoop, spoon seafood mixture onto bread and bake briefly in oven until seafood balls are lightly browned.