Marinha do Arvoredo

The Arvoredo Marine Biological Reserve (Reserva Biológica Marinha do Arvoredo) is Brazil's largest fully protected marine reserve along its southern coast, located approximately 11 km north of Florianópolis, Santa Catarina. Covering roughly 17,600 hectares of Atlantic Ocean waters, the reserve encompasses four islands—Arvoredo, Deserta, Galé, and Calhau de São Pedro—and the surrounding sea. Created in 1990 and managed by ICMBio, it protects critical marine ecosystems including rocky reefs, seagrass beds, and open water zones. The reserve is a no-take area where all extractive activities, fishing, diving, and anchoring are prohibited without scientific authorization.

Arvoredo hosts exceptional marine biodiversity for the South Atlantic. South American fur seals (Arctocephalus australis) maintain a significant breeding colony on Ilha Deserta, one of the few such colonies along Brazil's coast. The reserve's waters support bottlenose dolphins (Tursiops truncatus), spinner dolphins, and occasional humpback and right whales during migration. Sea turtle species including the loggerhead (Caretta caretta) and green turtle (Chelonia mydas) nest on island beaches. The rocky reefs teem with garoupas (groupers), mullets, snappers, moray eels, and octopus, while pelagic species including tunas and billfish pass through open water zones seasonally.

The reserve's terrestrial vegetation on its islands represents fragments of coastal Atlantic Forest (Mata Atlântica), one of the world's most threatened biodiversity hotspots. Dense shrubland, pioneer species, and wind-pruned tree formations adapt to salt spray and thin soils. Offshore, the subtidal marine environment supports coralline algae communities and rhodolith beds, which form critical structural habitat for invertebrates and juvenile fish. The absence of seagrass meadows in most areas is compensated by extensive macroalgae communities. The islands' vegetation also provides critical nesting habitat for colonial seabirds, including large colonies of kelp gulls and Magellanic penguins.

The Arvoredo Islands are composed of Precambrian granitic and gneissic basement rocks, representing the ancient shield geology of the southeastern Brazilian coast. Rounded granite boulders and exfoliation features dominate island landscapes, shaped by millions of years of weathering and marine erosion. The underwater terrain includes rocky reefs, submarine walls, and boulders colonized by invertebrates and algae, dropping to sandy bottoms at 20–40 meters depth. The Arvoredo seamount-like reef structure creates upwelling conditions that enhance marine productivity. Pleistocene and Holocene sediments accumulate in sheltered bays, forming sandy beach habitats on the island margins.

The reserve sits within a subtropical climate zone (Köppen Cfa), influenced by the convergence of warm tropical waters from the Brazilian Current and cool Sub-Antarctic waters. Sea surface temperatures range from 17°C in winter (June–August) to 25°C in summer (December–February). Surface weather is dominated by alternating frontal systems and high-pressure ridges; storm swells from the south can reach significant heights during winter months. Visibility underwater is highly variable, ranging from 5 meters during turbid conditions to over 20 meters during calmer periods. The subtropical position means the reserve experiences distinct seasons that influence species composition and marine productivity throughout the year.

The islands within and around Arvoredo were visited by indigenous Carijó people for thousands of years before European contact. Portuguese navigators charted the coastline in the early 16th century, and the archipelago served as a maritime reference point for vessels traveling between Rio de Janeiro and the Río de la Plata. During the 18th and 19th centuries, small-scale fishing communities exploited local marine resources, and the islands occasionally served as refuge for shipwreck survivors. Larger-scale commercial and artisanal fishing expanded through the 20th century, contributing to the significant depletion of fish stocks that prompted the reserve's eventual creation.

The Arvoredo Marine Biological Reserve was established by federal decree on 05 March 1990, making it one of the pioneering marine protected areas in Brazil. Its creation followed recognition in the late 1980s that the concentration of islands and productive reef systems north of Florianópolis formed an irreplaceable marine sanctuary. The Brazilian environmental agency IBAMA initially managed the reserve, with jurisdiction later transferred to ICMBio upon its creation in 2007. Scientific research has been conducted under permit since the reserve's founding, resulting in baseline biodiversity studies. A management plan was developed that strictly prohibits all human extraction and recreational activities.

The Arvoredo Marine Biological Reserve is strictly closed to public access, including recreational diving, sport fishing, and tourism. No visitor activities or trails exist on its islands or in its waters. Scientific diving expeditions conducted under ICMBio permit have documented the reserve's remarkable biodiversity and served as long-term monitoring studies tracking reef fish recovery since protection. The fur seal colony on Ilha Deserta is one of the few publicly known highlights but can only be observed from research vessels with special authorization. The reserve is occasionally cited in Brazilian media as a benchmark for marine recovery when extractive pressure is removed.

No public visitor facilities exist within the Arvoredo Marine Biological Reserve. The closest services and accommodation are available in Florianópolis, Santa Catarina's capital, which has a major airport (Hercílio Luz International Airport), ferry terminals, and extensive hotel infrastructure. The reserve boundary lies approximately 11–15 km offshore and can be seen on clear days from the northern beaches of Florianópolis Island. Authorized researchers travel to the reserve via boat from Florianópolis or nearby Governador Celso Ramos. ICMBio's Florianópolis office coordinates all research permit applications. The surrounding waters outside the reserve boundary are open to regulated artisanal fishing.

Since its establishment in 1990, the Arvoredo reserve has demonstrated measurable recovery of marine fish populations, particularly groupers and snappers that were severely depleted by decades of commercial fishing. It functions as a spawning aggregation refuge and larval source, exporting recruits to adjacent fishing grounds. Key conservation threats include illegal fishing within reserve boundaries, marine debris accumulation, anchoring damage to reefs, and the effects of warming sea surface temperatures on corals and algae communities. ICMBio conducts periodic patrols with vessel support, though enforcement capacity remains stretched. The reserve collaborates with Projeto Albatroz and other NGOs on seabird and marine mammal monitoring.