Nuanced impacts of the invasive aquatic plant Crassula helmsii on Northwest European freshwater macroinvertebrate assemblages

Samuel Tasker, Andrew Foggo, Kevin Scheers, Janneke van der Loop, Salvatore Giordano, David Bilton

Research output: Contribution to journalA1: Web of Science-articlepeer-review


Invasive alien species are considered one of the greatest threats to global biodiversity, and are particularly problematic in aquatic systems. Given the foundational role of macrophytes in most freshwaters, alien aquatic plant invasions may drive strong bottom-up impacts on recipient biota. Crassula helmsii (New Zealand pygmyweed) is an Australasian macrophyte, now widespread in northwest Europe. Crassula helmsii rapidly invades small lentic waterbodies, where it is generally considered a serious threat to native biodiversity. The precise ecological impacts of this invasion remain poorly understood, however, particularly with respect to macroinvertebrates, which comprise the bulk of freshwater faunal biodiversity. We conducted a field study of ponds, ditches and small lakes across the core of C. helmsii's invasive range (United Kingdom, Belgium and the Netherlands), finding that invaded sites had higher macroinvertebrate taxon richness than uninvaded sites, and that many infrequent and rare macroinvertebrates co-occurred with C. helmsii. Alien macroinvertebrates were more abundant in C. helmsii sites, however, particularly the North American amphipod Crangonyx pseudogracilis. At the order level, water beetle (Coleoptera) richness and abundance were higher in C. helmsii sites, whereas truefly (Diptera) abundance was higher in uninvaded sites. Taxonomic and functional assemblage composition wereboth impacted by invasion, largely in relation to taxa and traits associated with detritivory, suggesting that the impacts of C. helmsii on macroinvertebrates are partly mediated by the availability and palatability of its detritus.The nuanced effects of C. helmsii on macroinvertebrates found here should encourage further quantitativeresearch on the impacts of this invasive plant, and perhaps prompt a more balanced re-evaluation of its effects onnative aquatic macrofauna.
Translated title of the contributionGenuanceerde impact van het invasieve watercrassula (Crassula helmsii) op Noordwest Europese zoetwater macroinvertebraten gemeenschappen
Original languageEnglish
Article number193
JournalScience of the total environment
Pages (from-to)1-13
Number of pages13
Publication statusPublished - 1-Jan-2024

Thematic List 2020

  • Invasive species
  • Water

Thematic list

  • Still waters
  • Invasive species (management)

EWI Biomedical sciences

  • B003-ecology

Taxonomic list

  • water scavenger beetles (Hydrophilidae)
  • macroinvertebrates
  • plants (Plantae)


  • invasive alien species regulation (EU)
  • biodiversity policy

Geographic list

  • United Kingdom
  • Belgium
  • Netherlands

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