Taxonomic and functional diversity of mollusk assemblages in a tropical rocky intertidal zone

Abstract

ABSTRACT We investigated the spatial variation of molluscan assemblages with different habitat-forming species and bare rock habitat in a rocky intertidal zone in northeastern Brazil. The high intertidal zone substrate was covered predominantly of barnacles [Chthamalus bisinuatus (Pilsbry, 1916)], the mid-intertidal of mussels [Brachidontes exustus (Linnaeus, 1758)] and the low intertidal of macroalgae chlorophytes [Gayralia oxysperma (Kützing) K. L. Vinogradova ex Scagel et al., 1989 and Ulva lactuca Linnaeus, 1753], phaeophytes [Sargassum vulgare C. Agardh] and rhodophytes [Palisada flagellifera (J.Agardh) K. W. Nam, 2007]. A total of 3,861 mollusks were recorded, belonging to the classes Gastropoda (9 species; 3,800 individuals), Bivalvia (3 spp.; 54 ind.), and Polyplacophora (1 sp.; 7 ind.). Functional diversity was accessed through the trophic structure, in which we identified food guilds: suspension feeders, grazers, herbivores, and carnivores. The analysis revealed significant differences in mollusk abundance, species richness, diversity indices, and trophic diversity among barnacle belts, mussel beds, algae habitat, and bare rock habitats. The highest species richness and trophic diversity were detected in algae habitat and mussel beds, which showed low abundance. In contrast, barnacle belts registered low species richness and trophic diversity and a high number of individuals. Bare rock recorded low values in all surveyed indices. This result points to the effect of environmental modification caused by habitat-forming species in this system. These species increase environmental complexity and enable the establishment of organisms through facilitation processes. The various food guilds found in this study reaffirm the role of habitat-forming species in providing niches that support different occupation patterns.