Hanifaru Bay is a dead-end pocket of reef on the eastern rim of Baa Atoll, barely the size of a football pitch, yet it draws the largest gatherings of reef manta rays known anywhere on Earth. During the southwest monsoon, currents and tides push plankton-rich water against the outer reef and funnel it into the bay's single narrow mouth, where the flow stalls in a back-eddy and thickens the plankton into a dense soup. Reef mantas arrive by the dozen, up to two hundred at once, and when the food grows rich enough they lock into slow, spiraling columns known as cyclone feeding, mouths agape and wingtip to wingtip, barrel-rolling over and under one another so none goes hungry. Whale sharks sometimes join the feast. The bay lies at the heart of the Baa Atoll UNESCO Biosphere Reserve, designated in 2011 largely because of this single phenomenon, and Maldivian law has protected it as a Marine Protected Area since 2009.
In the water the scale is disorienting: dozens of mantas, each up to four metres across, wheeling through clouds of plankton lit by shafts of surface light, close enough that a careless kick could brush one, which is exactly why touching them is forbidden. Scuba is banned, since rising bubbles scatter the feeding animals, so snorkelers hold at the surface while rangers cap the crowd near eighty visitors a day and about forty-five minutes each. Boats are called in only when biologists watching the bay confirm the mantas have gathered. The feeds cluster around the new and full moons, when the strongest spring tides drive the richest plankton through the channel, and the water is clearest in the mid-morning hours before the afternoon wind picks up.