Rocas atoll (03°50′S, 33°49′W) located 230 km offthe northeastern coast ofBrazil. This is the only atoll in the SWA, and is one ofthe smallest in the world, with a total area of 5.5 km2. Rocas is mainly composed of a coralline algal-vermetid gastropod association and is part of a seamount chain known as the Fracture Zone of Fernando de Noronha. At this atoll, two sandy cays lie on the western side ofthe reefflat and several pools ofvarious sizes and depths are found within the atoll. Some of these pools remain connected with the open ocean (open pools) during low tide, whereas others do not (closed pools). The tidal regime that affects the atoll is semidiurnal and mesotidal, with maximum amplitudes of 3.8 m.