Influence of the Amazon River plume on the biodiversity and assemblage structure of lanternfishes (Myctophidae)

Abstract

Lanternfishes (Myctophidae) are among the most abundant vertebrates globally, playing critical roles in carbon transport, nutrient recycling, and trophic structuring of pelagic ecosystems. However, they remain poorly understood and are increasingly impacted by anthropogenic activities. Here we investigated how the plume of the world's largest river, the Amazon, shapes the diversity and assemblage structure of lanternfishes. To this end, we conducted an integrative characterization of the taxonomic diversity, distribution, and abundance of 2916 lanternfish specimens, representing 31 species, collected during the dry season (August–September 2021) across areas with varying levels of Amazon River plume influence. Based on a classification of relative importance, five species were classified as abundant and frequent, while the remaining species were predominantly classified as either scarce and frequent (nine species) or scarce and rare (17 species). In regard to vertical distribution, at least 20 of the 31 species were detected at night in epipelagic waters (0–200 m), displaying four distinct broad patterns of vertical migration and distribution. We showed that, while the Amazon Plume appears to influence lanternfish species richness and size distribution, depth is the primary variable explaining the structuring of lanternfish assemblages. Moreover, while diversity appears to be similar to other tropical regions of the Atlantic Ocean, there is a noticeable dominance of certain species, suggesting that the hydrographic structure and nutrient input from the Amazon River may favour specific species.