Spatial and Seasonal Variation of Species Richness and Biomass of Macroalgae (Rhodophyta) on Mangrove Roots on the Brazilian Amazon Coast

Abstract

Mangrove forests are a relevant coastal ecosystem, and Brazil holds the second-largest mangrove area worldwide, with over two-thirds of it located in the Amazon region. However, despite their singular environmental characteristics and ecological importance, macroalgal communities in Amazonian mangroves remain poorly understood. Therefore, this study investigates the composition and biomass of macroalgae from two mangrove forests on the Brazilian Amazon coast and their temporal variation. Overall, higher precipitation was observed in May and lower in September, while air temperatures were higher in November and lower in January. Estiva tidal creek exhibited higher salinity and conductivity, while Taici had higher turbidity, NO₂⁻, and PO₄⁻³ levels. Seven Rhodophyta species were identified, with Bostrychia calliptera, B. moritziana, and Catenella caespitosa being the most frequent and dominant in terms of biomass across all months and substrates at both sites. Richness and biomass varied significantly across months, with the highest values observed in the dry season (September) and at the innermost site (Taici). Among the substrates, rhizophores had significantly higher biomass in Taici, whereas pneumatophores showed similar biomass across both sites. DistLM analysis indicated that salinity, precipitation, NO₂⁻ concentrations, and substrate type were the main drivers of macroalgal biomass. These findings highlight the significant spatial and temporal variations in environmental conditions and macroalgal biomass in mangrove ecosystems, emphasizing the need for site-specific management and conservation strategies.