Ilha Redonda

Ilha Redonda holds an archaeological site discovered in 2012, regarded as a testimony to the navigation and climbing skills of the Tupi-Guarani people of the Rio coast. The island's ceramic and stone artefacts, many with Tupiguarani features and some with elements of contact with the Portuguese, point to intense and repeated occupation, contemporary with colonial contact. Redonda is the highest island in the area, and the tree Gymnanthes nervosa, once considered extinct in the city of Rio de Janeiro, was recorded on its summit. The island is especially important for seabirds: it hosts one of the largest breeding colonies of frigatebirds in the entire South Atlantic. At the peak of the breeding season there are more than 220 nests, making it the second-largest frigatebird breeding colony on the Brazilian coast, with about 5,500 birds.

Underwater, on the westward ascent, schools of brown chromis (Chromis multilineata) feed over a bottom of large boulders. On the plateaus there are sea urchins, variegated urchins (Lytechinus variegatus) grazing on algae beds and small colonies of brain coral (Mussismilia hispida), while scorpionfish camouflage themselves among the rocks. Where the rocky shore meets the sand and gravel bottom, fish restricted to deeper, colder waters appear, such as Acanthistius brasilianus, the butterflyfish Prognathodes guyanensis and Pronotogrammus martinicensis. This gathering of species is one of the underwater attractions of the Cagarras Islands Natural Monument. Around Rio's islands there are sites where diving is possible practically all year round.