Gradientes de sucessão de manguezais nos estuários dos rios Marapanim, Mojuim e Mocajuba

Abstract

The Paraense mangroves are the subject of the integrated project funded by FUNTEC-SECT AM on natural resources, social use and sustainability indicators. This work is a contribution to the knowledge of the interrelations between mangrove successional gradients and geomorphological processes acting in the Marapanim and São Caetano de Odivelas estuaries. In the latter, four successional patterns (two erosion and two accretion) were preliminarily identified with the support of remote sensing, videography and field work. The monitoring described in this paper was done in a sector of recent accretion, in the south of Ilha Nova, along a S/N transect of low gradient, flooded by tides and subdivided into three experimental plots. Spartina brasiliensis (Poaceae) clumps dominate the lower part, with some Avicennia nítida and Rhizophora mangle seedlings. The vegetation cover of the soil is discontinuous and weak <1 %). In the following plots the plant species are the same, but the ground vegetation cover is variable: young trees of small size <4 m) mainly of Avicennia nítida predominate while Spartina brasiliensis decreases considerably. The highest part of the land, constitutes a plateau with dense vegetation, formed by Spartina brasiliensis and the above mentioned woody species (more abundance of Rhizophora mangle). The presence of a layer of organic matter created by the decomposition of the vegetation is evident in the sediment samples collected there. The observations made at Ilha Nova (formed after 1977) are especially interesting: this island, therefore, is an excellent laboratory for the study of the speed and conditions of establishment of the pioneer mangroves in São Caetano Bay.