It’s low tide in Zanzibar, a semi-autonomous archipelago off Africa’s eastern coast, as a group of women in brightly colored clothing gather on the beach, and then walk into the sea. They are seaweed farmers, responsible for growing the aquatic plants that are Zanzibar’s largest marine export.

Men hold most of the jobs in this conservative Muslim society, but more than 80 percent of seaweed farmers here are women. Over the past few decades, trade in seaweed has brought them unprecedented financial independence — and the social status that comes with it.