A well-defined barnacle community was observed along the upper intertidal zone, from the euhaline to the oligohaline sector, with the cover area being larger in the euhaline sector. This study aimed to (i) describe the distribution patterns of chthamalid barnacles along the Paranaguá Estuarine Complex (PEC) and (ii) evaluate the vertical distribution of species in places where substantial coexistence was observed to preliminarily test whether their distribution is compatible with a lottery model of resource acquisition or compatible with a process of interspecific interference competition. In estuaries, two other species, Chthamalus proteus and Microeuraphia rhizophorae, may occur on hard substrates, although patterns of coexistence at relevant spatial scales are presently unknown, which prevents a better understanding of the ecology of rocky shore systems in the region. In southeastern Brazil, the upper intertidal zone of exposed rocky shores is typically colonized by the barnacle Chthamalus bisinuatus. Under these conditions, interspecific interactions may become relevant. However, certain environmental conditions may hinder resource monopolization by a dominant species, allowing for the coexistence of species. Distribution patterns in the upper intertidal zone, where diversity is low, are often explained by the variation in physical factors.
