Declines in Freshwater Mussels and Loss of Mussel–Invertebrate Interactions in the Subtropical Waterbodies of Dhaka, Bangladesh

Abstract

ABSTRACT Freshwater mussels are a globally threatened taxon, but little is known about population trajectories for species outside Europe and North America. To contribute to understanding of mussel conservation status outside these regions, we surveyed mussel and other invertebrate populations in waterbodies across Dhaka, Bangladesh, to assess population trends and the role of mussels in structuring benthic communities. We found that mussel populations in Dhanmondi Lake, our focal waterbody, have declined in density by approximately 90% between 2010 and 2023. Lamellidens marginalis declined by 90.8% from an average density of 47.9 ± SE 7.1 mussels 0.25 m−2 in 2010 to 4.4 ± SE 0.7 mussels 0.25 m−2 in 2023, while Indonaia caerulea declined by 89.4% from an average density of 6.6 ± SE 1.0 mussels 0.25 m−2 in 2010 to 0.7 ± SE 0.1 mussels 0.25 m−2 in 2023. Previously detected associations between mussels and other invertebrate taxa, and between mussels and community composition, have been lost. Non‐mussel invertebrates have also declined significantly, with an average decrease in abundance of 27%, alongside decreases in family richness and Shannon‐Wiener diversity. These declines occurred despite apparent improvements in water quality. Findings from other waterbodies across Dhaka also suggest the loss of mussel species including L. marginalis, I. caerulea and Parreysia corrugata from some locations, as well as the presence of the non‐native mussel Pilsbryoconcha exilis at river sites. Our results reflect a wider, global pattern of enigmatic declines in freshwater mussels and the possible loss of associated ecosystem functioning, which may be going unnoticed in less‐studied areas including the subtropics.