Amazonian freshwater mussel density: A useful indicator of macroinvertebrate assemblage and habitat quality

Abstract

Mussels have important ecological functions in freshwater ecosystems, but populations are declining in many rivers worldwide. In the Amazon, which is undergoing widespread human-mediated alterations, information on mussel ecology is lacking. We investigated whether declines in mussel density, due to exploitation, are associated with lower macroinvertebrate assemblage taxon richness and modified habitat functioning in an Amazonian river. Between 2015 and 2017, macroinvertebrate metrics of abundance and number of families, and related habitat variables, were compared between exploited and unexploited mussel beds in the Caeté river, northeastern Pará state, Brazil. Except for Chironomidae abundance, which increased, other macroinvertebrate metrics decreased in exploited mussel beds, especially abundances of shredders and predators. Medium and high mussel densities appear to support abundant and diverse macroinvertebrate assemblages. Macroinvertebrate decreases were mainly correlated with lower organic matter in the sediment and higher dissolved solids in the water column, due to losses in mussel biodeposition and filtration functions. Amazonian freshwater mussel density is a useful indicator of abundant and diverse macroinvertebrate assemblages, and mussel beds may help prioritize locations for habitat conservation in Amazonian rivers, and indirectly for fishes that are essential for mussel dispersion. Aquatic management efforts should explicitly include mussel beds and their diverse associated macroinvertebrate assemblages.

Keywords

• Bivalve declines
• Biodiversity
• Ecological functions
• Exploitation
• Functional groups
• Management