Ilha do Castilho

Ilha do Castilho, 7.4 km off the coast and with 7.32 ha of land above water, is part of the Estação Ecológica dos Tupiniquins, created by Decree 92.964 of 21/07/1986 to conserve the island ecosystems of the southern coast of São Paulo. Around the island, the submerged archaeological site Castilho 1 was identified; it probably corresponds to the Soares, a coastal trading boat sunk between the 1950s and the 1960s. This boat is thought to have been one of the last coastal trading vessels linking the ports of southern Brazil to those of southern São Paulo State. There is also a record of a fire on the island in the 1970s, started by fishermen camping there.

In a survey of reef fish, Castilho and Queimada Pequena, the islands farther from the coast, had more species per sample than Cambriú, which is closer to the mainland. On the sheltered side of the island zoanthids predominate, but no brain corals of the genus Mussismilia, which are present at Queimada Pequena, were observed. On the rocky shores, the saquaritá snail (Stramonita haemastoma) is the only abundant predatory gastropod and feeds on barnacles and bivalves. Rare or hard-to-collect molluscs have also been found at Castilho, such as the bivalves Codakia orbicularis and Tellina brasiliensis and the gastropod Cerithiopsis emersoni.

Above water, on 14/07/1990 a brown booby (Sula leucogaster) chick received band U 133 01 on the island, perhaps the first insular seabird banded on the São Paulo coast. A land snail of the genus Drymaeus, studied as a possible new species, was also found on the emerged part of the island.