Pemba is an island group to the north of the Zanzibar archipelago, Tanzania. Its mosaic of forests, swamps, mangroves and lagoons is scattered with ruined mosques and tombs – now reclaimed by the forest. In the channels between the islands are submerged reefs, thickly crusted with a mixture of sponges, corals and seaweed. In the water above, schools of manta rays feed on the rich supply of plankton.