From roots to burrows: how Spartina alterniflora (Poaceae) structure modulates brachyuran diversity in Amazonian saltmarshes

Abstract

Saltmarshes dominated by Spartina alterniflora are highly productive coastal ecosystems that play key roles in sediment stabilization, organic matter accumulation, and the maintenance of benthic communities. While the ecological influence of S. alterniflora on macrofauna is well documented in temperate and subtropical regions, however, few studies about these interactions in the Amazon coast are reported. Based on that, this study evaluated the effects of S. alterniflora vegetation structure on the abundance, richness, and composition of Brachyuran crabs in saltmarshes at Maçarico Beach, Salinópolis, Pará, Northern Brazil. Fieldwork was conducted in June 2019 comparing two transects with contrasting vegetation zones. Vegetation attributes (above- and belowground biomass, height, organic matter content) and crab assemblage metrics (abundance, species richness, burrow density) were analyzed using ANOVA, PERMANOVA, and multivariate ordinations. Structurally complex areas with taller stems, higher root biomass, and greater organic matter content supported significantly higher crab abundance, richness, and burrow density. Community composition also varied between zones, with Uca maracoani and Minuca sp. dominating vegetated areas, while Callinectes bocourti was associated with less vegetated zones. These findings indicate that crab distribution in Amazonian saltmarshes is strongly associated with vegetation complexity, underscoring the ecological relevance of conserving S. alterniflora habitats under increasing coastal pressures.