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 5,009 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%, whilst 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 macro..., Abundance data for riverine macroinvertebrates in England were extracted from the EA’s ecological monitoring database. The data were filtered to only include three-minute kick-sample data as the primary method for sampling freshwater invertebrates (approximately 99% of samples). Three-minute kick-samples are a standardised, internationally-recognised, semi-quantitative approach to assessing macroinvertebrate ecology and water quality in rivers using invertebrate diversity indicators. Prior to the implementation of the European Union Water Framework Directive in 2000, abundance estimates were based on categories (0–9, 10–99, 100–999 etc.). In 2002, the EA started recording more exact abundance estimates and enacting improved quality control procedures, whereby one in every ten samples was independently re-analysed. Hence, although the original dataset covered sampling years from 1991, our analysis was restricted to the years 2002–2019. Data were further filtered to only include sites sam...,