To me, I believe these lines represent the different forms and tasks of slavery/slaves in America. The slaves in the country were asking about the black berries, like the harvesters on fields that were in the ocean, where they thought life would be better. The slave, equally as distraught asked them about the dark ships, which I believe are slave ships, in the country. This to me showed that they thought there was a better way of life for them available at the time, but truly every black man and woman was struggling with whatever task was put upon them.