Makes 6 breakfast, brunch side dish, or dessert servings.
Remove zest from 1 lime in strips with a vegetable peeler and cut any white pith from strips with a sharp knife. Squeeze 3 tablespoons juice from limes. Bring zest, water, and sugar to a boil in a 1/quart saucepan, stirring, until sugar is dissolved, then boil, uncovered, about 3 minutes. Remove from heat and stir in lime juice. Let syrup stand 20 minutes, then remove zest with a slotted spoon and discard.
Toss together mangoes, blueberries, and syrup in a large bowl and sprinkle with ginger.