Abundance trends for river macroinvertebrates vary across taxa, trophic group and river typology

There is mounting evidence that terrestrial arthropods are declining rapidly in many areas of the world. It is unclear whether freshwater invertebrates, which are key providers of ecosystem services, are also declining. We addressed this question by analysing a long-term dataset of macroinvertebrate abundance collected from 2002 to 2019 across 5009 sampling sites in English rivers. Patterns varied markedly across taxonomic groups. Within trophic groups we detected increases in the abundance of carnivores by 19% and herbivores by 14.8%, while we estimated decomposers have declined by 21.7% in abundance since 2002. We also found heterogeneity in trends across rivers belonging to different typologies based on geological dominance and catchment altitude, with organic lowland rivers having generally higher rates of increase in abundance across taxa and trophic groups, with siliceous lowland rivers having the most declines. Our results reveal a complex picture of change in freshwater macroinvertebrate abundance between taxonomic groups, trophic levels and river typologies. Our analysis helps with identifying priority regions for action on potential environmental stressors where we discover macroinvertebrate abundance declines.

Automated summary

There is a growing body of evidence suggesting that terrestrial arthropods are rapidly declining worldwide. However, it remains uncertain whether freshwater invertebrates, which play a crucial role in ecosystem services, are also experiencing declines. In this study, a long-term dataset from 2002 to 2019 of macroinvertebrate abundance in English rivers was analyzed. The findings revealed varied patterns across taxonomic groups and trophic levels, indicating a complex picture of change in freshwater macroinvertebrate abundance. The results contribute to the identification of priority regions for addressing potential environmental stressors causing declines in macroinvertebrate abundance.