Rainfall Influences the Patterns of Diversity and Species Distribution in Sandy Beaches of the Amazon Coast

The Amazon region is one of the Earth's hotspots of biodiversity and has a pivotal role in climate regulation. Yet, little is known about its coastal biodiversity. Here, we performed the first assessment of macrobenthic diversity and ecological patterns of sandy beaches north of the Amazon River delta, the world's largest freshwater input into the oceans. By assessing spatial and temporal changes in the soft-bottom biodiversity and environmental variables of three beaches (Goiabal, Nazare, and Sumauma) in the northernmost stretch of the Brazilian coast, we found low richness (14 taxa, overall; Goiabal: 3.27 +/- 1.78; Nazare: 2.34 +/- 1.29; Sumauma: 2 +/- 0.67) and diversity (Goiabal: 0.72 +/- 0.52; Nazare: 0.62 +/- 0.46; Sumauma: 0.55 +/- 0.39) across 2949 individuals with great dominance of estuarine species (notably Nephthys fluviatis and Sphaeromopsis mourei). Abundance was higher during rainy periods, and the same pattern was observed for richness and diversity in comparison to transitional periods, at least on Nazare Beach. Environmental heterogeneity was reduced during rainy periods, resulting in a higher abundance of dominant species and lower beta diversity. Most species presented aggregated distribution at the upper intertidal zone, and changes in macrobenthic assemblages were linked to variations in rainfall and organic matter content in the sediment. Given the ecological uniqueness and the severe erosional process affecting the northern coast of the Amazon region, our results provide essential baseline knowledge to better understand the patterns and processes influencing its understudied biodiversity. We advocate that further studies expand our findings to support the conservation of this region.

Automated summary

This study provides the first assessment of the biodiversity and ecological patterns of sandy beaches in the Amazon region. The findings show low diversity and dominance of estuarine species, with abundance and diversity influenced by rainfall and organic matter content in the sediment.