Rocas Atoll

• Category: Marine and Oceanic Biomes.
• Geographic Location: South America.
• Summary: The only atoll in the southwestern Atlantic, Rocas has enormous ecological importance as a zone of shelter and reproduction for several species of seabirds and marine turtles.

The first biological marine reserve to be created in Brazil, the Rocas Atoll is a reef formation located 162 miles (260 kilometers) off the coast of the state of Rio Grande do Norte in northeastern Brazil, and 91 miles (146 kilometers) west of the Fernando de Noronha Archipelago. The atoll was discovered by Gonçalo Coelho, who left Lisbon in May 1503 with a fleet of six ships and Florentine navigator Americo Vespucci among the crew members. The expedition, which aimed to recognize and explore the territory that belonged to the Portuguese crown according to the Treaty of Tordesillas, was financed by Portuguese traders who were interested in raw materials from the new continent. The atoll was first documented on the sixteenth-century map of Cantino, while the first detailed chart, dating to 1852, was provided by Captain Lieutenant Phillip Lee.

One of the smallest atolls on Earth, and the only example in the southwestern Atlantic, Rocas (from the Spanish word for rocks) was formed primarily by vermetids, or worm snails, and coralline algae—rather than corals. The elliptical atoll is 2.3 miles (3.7 kilometers) long and 1.6 miles (2.5 kilometers) wide, with a surface of 79,074 acres (32,000 hectares), of which 17 acres (6.7 hectares) is land. Its reef ring, which is visible during low tide, consists of a natural wall 5 feet (1.5 meters) high bordered by sand banks, interrupted by a 656-foot (200-meter) passage on the northern side and by a smaller channel on the western side. Inside the atoll is a large lagoon of 2.7 square miles (7.1 square kilometers), in addition to several shallow pools 3–16 feet (1–5 meters) deep.

The two small islands, Farol (meaning lighthouse) and Cemitério (cemetery), were formed by submarine mountain rock substrate and white “false” sand, which is composed of limestone, broken coral, and bones of birds and fish. At low tide, both islands become connected to Rocas, and the water in the pools is renewed. During high tide, only the islands remain exposed. Farol, the larger of the two, has a stretched “S” form; it is approximately 3,281 feet (1,000 meters) long and 656 feet (200 meters) wide, and reaches a maximum height of 10 feet (3 meters) above sea level.

The climate is tropical, and the rainy season lasts from January to August. Average annual rainfall is 29 inches (731.5 millimeters), but from March to July, this volume can mount to 7 inches (190 millimeters) in 24 hours. The average temperature varies from 74 to 89 degrees F (23.5–31.5 degrees C), and the relative humidity remains around 81.5 percent throughout the year.

Biodiversity

The Rocas Atoll has dense herbaceous vegetation that is resistant to high levels of salinity, sunlight, and variation of the tides. Species of amaranths anchored by dense tangles of rhizomes are found closer to the sea, whereas species of Portulacaceae, Cyperaceae, Graminae, and Amaryllidaceae grow farther inland. The area also has scattered coconut trees introduced by fishers.

A total of about 150,000 individuals of 30 different species of birds have been identified in the atoll area. Five of them are endemic, or found nowhere else on the planet: the masked and the brow booby (Sula dactylatra and S. leucogaster, respectively), the brown and the black noddy (Anous stolidus and A. minutus), and the sooty tern (Sterna fuscata). Rocas shelters the largest breeding colonies of Sula dactylatra and Anous stolidus in Brazil, and of Sterna fuscata in the South Atlantic.

Migratory species include the white tern (Gygis alba), red-footed booby (Sula sula), magnificent frigate (Fregata magnificans), and red-billed tropic bird (Phaethon aethereus), characterized by its long tailfeathers.

Two species of lizard occur on the island: the endemic Mabuya maculata and Tupinambis teguxim. Although the latter was introduced to control rat populations, it preys on both the eggs and live young of birds and turtles. There are no mammals on the island.

Rocas Atoll is the second-largest reproductive area for green turtles (Chelonia mydas) in Brazil, after the volcanic island of Trindade. Since 1987, a program of the combined Projecto Tartarugas Marinhas (TAMAR) and the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA) has been monitoring major populations of marine turtles in the archipelago. In 1990, the TAMAR-IBAMA project launched its first actions aimed at preserving these species. By the end of 1993, a permanent research station was established in the area.

Marine biodiversity is rich in the atoll, which is used by many fish species for spawning and as a refuge for juvenile fish. The shallow, warm waters also provide habitat for benthic, or bottom-dwelling, organisms such as algae (100 species), sponges (44 species), and coral (seven species). Of the 150 species of fish identified in the Rocas reserve, only two are exclusive to the area.

Conservation Efforts

Rocas is the first Brazilian biological marine reserve, created June 5, 1979. Together with Fernando de Noronha, the Rocas Atoll bears important habitats for migratory seabird populations and for marine-turtle nesting, and is a key site for the protection of biodiversity and endangered species in the Southern Atlantic. In 2001, the Biological Marine Reserve of Rocas Atoll was designated a World Heritage Site.

The waters surrounding the Rocas Atoll harbor important stocks of commercial fishes and crustaceans, which were one draw for heavy fishing activity around the atoll in the past. Visits to this natural reserve now are limited to scientific expeditions; the trip to Rocas takes about 26 hours, departing from Natal in Rio Grande do Norte. In general, teams consist of two IBAMA agents responsible for watching over the area, and additional members including scientists, students, and volunteers.

Warming temperatures from climate change could disturb the critical habitats here, disturb the intertidal zones and cause inundation above the shoreline, potentially weaken the immune response of the corals, and generally stress both flora and fauna. The same pressures could also allow new invasive species to enter the atoll.

Bibliography

Banha, Thomás Nei Soto, et al. "Low Coral Mortality During the Most Intense Bleaching Event Ever Recorded in Subtropical Southwestern Atlantic Reefs." Coral Reefs vol. 39, 2020, 515-21. link.springer.com/article/10.1007/s00338-019-01856-y. Accessed 30 Nov. 2024.

Garcia, K.B.L. "Modern Sedimentation and Morphology of the Rocas Atoll Shelf, and the Role of Quaternary Sea-Level Changes." Regional Studies in Marine Science, vol. 53, June 2022, doi.org/10.1016/j.rsma.2022.102354. Accessed 30 Nov. 2024.

Kenji Papa de Kikuchi, Ruy. “Rocas Atoll, Southwestern Equatorial Atlantic, Brazil.” In C. Schobbenhaus, D. A. Campos, E. T. Queiroz, M. Winge, and M. Berbert-Born, eds., Sítios Geológicos e Paleontológicos do Brasil. Brasilia: Brazilian Commission of Geological and Palaeobiological Sites, 2002.

Schulz Neto, A. “Aspects of Seabird Biology at Atol das Rocas Biological Reserve, Rio Grande do Norte, Brazil.” El Hornero 15, no. 1 (1998).

United Nations Educational, Scientific, and Cultural Organization (UNESCO). “Brazilian Atlantic Islands: Fernando de Noronha and Atol das Rocas Reserves.” UNESCO World Heritage Centre. . Accessed 30 Nov. 2024.

United Nations Environment Programme (UNEP). “Brazilian Atlantic Islands: Fernando de Noronha Archipelago and Atol Das Rocas Reserves.” whc.unesco.org/en/list/1000/. Accessed 30 Nov. 2024.