Patterns of mollusc distribution in mangroves from the Sao Marcos Bay, coast of Maranhao State, Brazil

The diversity and distribution of molluscs from the Amazon Coast of Maranhao State, Brazil, are poorly understood. The aim of this study was to investigate how molluscs in two mangrove creeks (Buenos Aires and Tronco) at the Sao Marcos Bay, coast of the Maranhao State, respond to spatial and temporal variations in the environment. Sampling was performed in the intertidal area along three zones established using a straight line transect of 100 m. Abiotic variables of water and sediment were measured at each creek. We found 5,912 specimens belonging to 23 species and 15 families of epifaunal and infaunal molluscs. The patterns of their distribution in the two creeks were different. Salinity, dissolved oxygen, and rainfall were the main variables that affected the temporal distribution of molluscs. We found low species richness in the overall mollusc composition. Diversity in the Buenos Aires Creek was lower than that observed in the Tronco Creek, possibly because of activities of a port located in proximity to the former. The spatial distribution of molluscs along the zones followed an abundance and diversity gradient, mainly influenced by exposure time during low tide. Port activities may influence the patterns of mollusc distribution in the surrounding mangroves, and we thus highlight the importance of management and monitoring of these areas.Original Abstract: A diversidade e distribuicao de moluscos na Costa Amazonica do Estado do Maranhao, Brasil, sao pobremente conhecidas. O objetivo deste estudo foi investigar como os moluscos em dois igarapes de manguezal (Buenos Aires e Tronco) na Baia de Sao Marcos, costa do Estado do Maranhao, respondem a variacoes espaciais e temporais no ambiente. A amostragem foi conduzida no entre-mares ao longo de tres zonas estabelecidas a partir de um transecto em linha reta de 100 m. As variaveis abioticas de agua e sedimento foram medidas para cada igarape. Foram contabilizados 5.912 especimes pertencentes a 23 especies e 15 familias na epifauna e endofauna. Os padroes de distribuicao de moluscos foram distintos entre os dois igarapes. Salinidade, oxigenio dissolvido e precipitacao foram as principais variaveis ??que influenciaram a distribuicao temporal dos moluscos. Observou-se baixa riqueza de especies na composicao geral de moluscos. A diversidade no igarape Buenos Aires foi menor do que a observada no igarape Tronco, possivelmente por causa das atividades portuarias nas proximidades do primeiro. A distribuicao espaci