Boundaries

This ecoregion includes all of the coastal drainages of eastern Brazil in the state of Rio de Janeiro between the Paraíba do Sul in the east and Restinga da Marambaia to the west. It is bound in the north by the Serra dos Órgãos, which forms part of the Serra do Mar and is noted for its unusual rock formations. The ecoregion also includes the drainages flowing into the Baía de Guanabara and other coastal lagoons and marshes, as well as coastal drainages of northern São Paulo.                                                                                                                                                                                                              

Topography

The Baxaida Fluminense (Fluminense lowlands) is a sedimentary plain bordered by the granitic and gneissic rocks of the Serra dos Órgãos escarpment to the north, which forms part of the Serra do Mar that separates the plain from the interior plateau. There are also isolated massifs of Precambian origin around the Baía de Guanabara. The bay itself is a flooded rift that resulted from the uplift of the Serra do Mar (Dillenburg & Hesp 2009).  Elevations range from sea level to over 2100 m in the Serra dos Órgãos. The coastal drainages are short and steep and dominated by high gradient streams.

Freshwater habitats

The streams and small rivers of this ecoregion originate in the Serra dos Órgãos and flow onto the coastal plain where they sometimes form freshwater or brackish lagoons. Of the numerous coastal lagoons and estuaries, some of the largest are Araruama, Guarapina, and Maricá. Lagoa de Araruama is the largest hypersaline coastal lagoon in Brazil, receiving freshwater inputs from the intermittent Rio das Moças and Rio Matarama (Kjerfve et al. 1996). The Fluminense coast also is marked by restingas and small barrier lagoons formed from sea level fluctuations. Both the Rio São João and Rio Macaé empty directly into the Atlantic, whereas the Rio Macucu first enters the Baía de Guanabara. This bay is drained by more than 45 small rivers, of which six provide more than 85% of the freshwater input (Kjerfve et al. 2001).

Terrestrial habitats

The indigenous vegetation of the ecoregion historically has been Mata Atlântica, with most remaining stands occurring along mountain slopes. Trees are dominated by the Leguminosae, Bignoniaceae, Lauraceae, and Sapotaceae families (Diegues 1995). The Serra do Mar is also an important center of diversity for Bromeliaceae. Mangrove wetlands line the Baía de Guanabara with species like Avicennia schauerania and Rhizophora mangle (Kjerfve et al. 2001).

Description of endemic fishes

Forty-two percent of the species are endemic to the Fluminense. Endemics comprise nine families, the largest of which is Rivulidae with 13 species, followed by Trichomycteridae with nine species. There and also two endemic genera: the monotypic catfish Trichogenes (T. longipinnis) and the killifish Nematolebias, represented by the Rio pearlfish (N. whitei) and N. papilliferus.

Justification for delineation

The Fluminense lies within Gery’s (1969) East Brazilian ichthyographic region, which was further refined by Ringulet (1975) into Southeastern Brazil. It is distinguished by a large percentage of endemics.

Level of taxonomic exploration

Good