Environmental Assessment and Aquatic Biodiversity Conservation of Amazonian Savannas, Marajó Island, Brazil

Abstract

Marajo Island is located in the mouth of the Amazon River, the World’s largest river, at its interface with the Atlantic Ocean (Goulding et al., 2003). Marajo is the World’s largest riverine island (Cruz, 1987), with a total area of approximately fifty thousand square kilometers (Fig. 1). In addition to the Amazon, the island is also influenced by the Tocantins River and other small rivers of the south (Barthem & Schwassmann, 1994; UNEP, 2004). The island is surrounded by sandy-clayey beaches, and encompasses a hydrographic system (rivers, channels, and creeks) which both drains and floods the terra firme forest and varzeas (swamps) (Marques-Aguiar et al., 2002). In addition to these forest ecosystems, the island’s lakes, lagoons, beaches, rivers, and mangroves contribute to its diversity of habitats and organisms (Marques-Aguiar et al., 2002; Montag et al., 2009; Almeida et al., 2009). This diversity of habitats influences the richness of the region’s fauna, including its fish, and plays an important role in habitat preferences and use (Lowe-McConnell, 1999; Carrier et al., 2004). Most of these environments are heavily influenced by the inundation cycle of the estuarine region, which Junk (1997) characterizes as a polymodal cycle of low amplitude, but highly predictable flood pulses, influenced primarily by the local tides. The climate of Marajo Island can be characterized by two categories of the Koppen classification system – Af (humid tropical, with mean precipitation in the driest month at least 60 mm) and Am, tropical monsoon, with excessive rainfall between February and May. During this period, two-thirds of the island are completely flooded (Cardoso & Pereira, 2002; Lima et al., 2005; Fig. 1). Annual precipitation on Marajo Island ranges between 2500 mm and 4000 mm, with a mean temperature of around 27oC, and relative humidity of 81% to 94%. Rainfall is distributed in two distinct periods, with a marked rainy season between January and June, and a dry season, between September and November. Despite this rigorous hydrological regime, the vegetation covering the part of the island that is flooded annually is referred to as a savanna (or flooded grassland; Fig. 2), which is known for the diversity and abundance of its fishery resources (Barthem & Fabre, 2003; Montag et al., 2009; Schaan, 2010). While the term savanna is more associated with specific floristic characteristics, comparable with those of the savannas of central Brazil (Eiten, 1972; Ratter et