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.
Highlights
This study documented the spatial variation in taxonomic and functional diversity of mollusk assemblages in different types of habitat in a tropical rocky intertidal zone
Variations in the mollusk assemblage structure were identified between barnacle belt, mussel beds, algae habitat, and bare rock habitats
Of the three taxonomic classes recorded, gastropods showed high abundance, species richness, and trophic diversity, having occurred in the four habitats investigated. This result is in line with that described for the rocky intertidal zone in other tropical regions (Flores-Rodríguezet al., 2012; Martinez et al, 2012), confirming gastropods affinity for these environments
Summary
Nós investigamos a variação espacial das assembleias de moluscos em função de diferentes habitats formados por fauna séssil e substrato rochoso em uma zona entre marés rochosa no nordeste do Brasil. Abundância, riqueza de espécies, diversidade de Shannon, uniformidade de Pielou e diversidade trófica variaram em função dos habitats formados por cracas, mexilhões, algas e substrato rochoso. Habitats formados por algas e mexilhões apresentaram elevada riqueza de espécies e diversidade trófica, entretanto, apresentaram baixa abundância. Biodiversity has been described through diversity indices based on species richness or evenness, with relative abundance (Villéger et al, 2010; Moreno et al, 2018) They provide meaningful information about the structure of biotic systems, they do not consider the functional identity of organisms (Orwin et al, 2014). To our knowledge there is only one previous study assessed the trophic structure of molluscan assemblages inhabiting different habitat types in a tropical rocky intertidal zone (Olabarria et al, 2001)
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