Radiography of the Brazilian coast in the last 37 years: stable mangroves, shrinking beaches and dunes
With 7491 kilometers, the Brazilian coastline places our country among the 20 countries with the longest coastline in the world. With the help of satellite images and artificial intelligence resources, MapBiomas has taken an X-ray of this territory, which includes beaches, dunes, mangroves, apincus, and aquaculture and saliculture areas. It also mapped municipalities in the interior of Brazil with large sandbars. The numbers show relative stability in these natural formations, with some gains in mangroves and the same trend of loss in beaches and dunes.
The good news comes from the mangroves, which extend all along the Brazilian coast from Amapá to Santa Catarina. Between 1985 and 2021, their total area expanded by 4%, from 970,000 hectares to more than one million hectares (1,011 Mha). Three northern states - Amapá, Pará and Maranhão - account for 80% of the country's mangrove cover and their configuration explains this good result. The mangroves in the north grow under a macromarine regime, whose water level has a daily variation of more than 4 meters, and develop over a mud plain that reaches 30 km wide, occupied by trees up to 30 m high, says Pedro Walfir, from the MapBiomas coastal zone mapping team. This type of natural cover makes this ecosystem naturally resilient to anthropic changes.
The mangrove is a nursery for countless marine species: 70 to 80% of the fish, crustaceans, and mollusks that the population consumes need this biome at some stage in their lives. Several economically important fish species use the mangroves as a breeding ground and then return to the sea. Mangroves are also important for protecting the coast from marine erosion.
Among the natural formations over which the mangrove expands are the apicuns - dynamic surfaces, hypersaline and associated with the tidal regime. Between 1985 and 2021, the apicuns increased from 57 thousand to 54 thousand hectares of area in Brazil. Maranhão concentrates approximately 60% of the country's apicuna surface area.
Most of its area (70%) is within one of the 340 Conservation Units of the Brazilian Coastal Zone. Despite this, between 1985 and 2021, 1,300 hectares of apicuns were converted for aquaculture activities, which, together with the 531 hectares lost to urban infrastructure, represents the main risk to this type of natural formation. "Apicuns, like mangroves, are locally dynamic, interspersing losses and gains of approximate magnitude over the time series. They are natural transformation processes," explains César Diniz, from MapBiomas' coastal zone mapping team. "However, when there is conversion to urban infrastructure or aquaculture, this dynamic is interrupted: there is no return to the original formation," he adds.
Aquaculture was the occupation of the Brazilian coastal zone that grew the most in the last 37 years: it had an increase of 36% between 1985 and 2021, going from 36 thousand hectares to 56 thousand hectares in the country. The activity expanded mainly on water surfaces (28%), mosaic of agriculture or pasture (25%), and savanna formation (14%), with a clear preference for non-vegetated regions, such as apicuns or, when vegetated, of shrubby size. Two states (Rio Grande do Norte, with 67%, and Ceará, with 15.4%) concentrate 82% of the salt culture / aquaculture area in Brazil. Mossoró, in Rio Grande do Norte, has the largest aquaculture / salt culture area in the country: approximately 11 thousand hectares - twice the urbanized area of the municipality.
Beaches, dunes and sand dunes lose 15% of their area
The scenario of beaches and sand dunes without vegetation cover is different: 47% of their area is in conservation units, which shrank from 457 thousand hectares in 1985 to 389 thousand hectares in 2021 - a 15% retraction. Among the vectors that led to this loss of 68 thousand hectares is the pressure of the real estate market and the consequent advance of urban infrastructure (11%), forestry (7.4%), pastureland and mosaics of agriculture and livestock (10%).
"This loss is worrisome because beaches and dunes play a strategic role in controlling coastal erosion and preserving biodiversity," explains César. "The beach and the dune usually protect the mangroves from the action of the waves, creating a calm environment where the mud can be deposited and colonized by the mangrove vegetation," he explains.
The Lençóis Maranhenses and the Cordão Dunar in Rio Grande do Sul are the two largest contiguous sandy features in Brazil. Together, they account for 51% of the country's beaches and dunes. But sand and dunes are not only found on the coast: according to MapBiomas, of the 10 municipalities with the largest extension of this type of coverage, two are in the interior of the country - Pilão Arcado and Xique-Xique, both in Bahia. The leading municipality is Barreirinhas, in Maranhão.