Abstract in Portuguese:

Resumo: Os manguezais são ecossistemas costeiros situados na zona de transição entre ambientes terrestres e marinhos, típicos de regiões tropicais, ocorrendo em áreas com submersão frequente pelas marés. Esses ecossistemas abrigam a espécie Rhizophora mangle L. (Rhizophoraceae), uma árvore de mangue que possui rizóforos, projeções do caule que servem como substrato para uma variedade de animais incrustantes, sedentários e espécies de macroalgas. Este estudo foi realizado em um manguezal estuarino no rio Acaraú, localizado no nordeste do Brasil, com o objetivo de determinar a comunidade bentônica estabelecida nos rizóforos de R. mangle. Para isso, cinco árvores dessa espécie foram selecionadas, e, em seguida, três rizóforos foram escolhidos de cada árvore, totalizando quinze rizóforos amostrados, dos quais todos os macrobentos associados foram removidos. Todos os organismos coletados foram identificados e os rizóforos foram avaliados quanto à riqueza de espécies, composição, densidade, diversidade, frequência, equitabilidade e dominância. Além disso, foi determinada a zonação vertical dos organismos nos rizóforos. A comunidade bentônica foi caracterizada pela predominância dos filos Mollusca (Bivalvia e Gastropoda) e Annelida (Polychaeta). Demonstramos a existência de uma zonação vertical dos organismos no substrato. A compreensão da estrutura da comunidade nos rizóforos pode facilitar estudos mais detalhados e experimentais para entender a distribuição e até mesmo as interações biológicas nesses ambientes.

Abstract in English:

ABSTRACT Mangroves are coastal ecosystems that exist in the transition zone between terrestrial and marine environments, typical of tropical regions, and they occur in areas with frequent tidal submersion. These ecosystems shelter the species Rhizophora mangle L. (Rhizophoraceae), a mangrove tree that has rhizophores, stem projections that serve as a substrate for a variety of encrusting, sedentary animals and macroalgal species. This study was carried out in an estuarine mangrove on the Acaraú River, located in northeastern Brazil, with the aim of determining the benthic community stablished over R. mangle rhizophores. Accordingly, five trees of this species were chosen, and subsequently, three rhizophores were selected from each tree, totaling fifteen sampled rhizophores, from which all associated macrobenthos were removed. All collected organisms were identified and rhizophores were evaluated for species richness, composition, density, diversity, frequency, equitability and dominance. In addition, vertical zonation of the organisms in rhizophores was determined. The benthic community was characterized by the predominant presence of the phylum Mollusca (Bivalvia and Gastropoda) and the phylum Annelida (Polychaeta). We showed the existence of a vertical zonation of the organisms in the substrate. Understanding the community structure in the rhizophores can facilitate more detailed and experimental studies to comprehend the distribution and even the biological interactions in these environments.

Abstract in English:

ABSTRACT The family Pycnothelidae comprises medium to small-sized spiders that construct silk tubes under stones or logs or dig burrows in open environments. In Argentina, Acanthogonatus centralis Goloboff, 1995 and Stenoterommata platensis Holmberg, 1881 are two species commonly found in central region, associated to the mountainous grasslands or to the La Plata River Basin. The Tandilia mountainous grassland is an extended belt located southeastern Buenos Aires province, Argentina. Although some pycnothelid spiders are distributed close to this mountainous system, they are not recorded in Tandilia. Through niche modeling we attempt to evaluate the influence of bioclimatic variables in shaping the distribution of these species and explore their absence in the mountainous belt under past, present and future climatic conditions. We found that Tandilia is a non-suitable area for the establishment of the populations of these species with the exception of Stenoterommata platensis under a future scenario of climatic change.