ORCID

Abstract

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 true fly (Diptera) abundance was higher in uninvaded sites. Taxonomic and functional assemblage composition were both 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 quantitative research on the impacts of this invasive plant, and perhaps prompt a more balanced re-evaluation of its effects on native aquatic macrofauna.

Publication Date

2024-01-05

Publication Title

Science of the Total Environment

Volume

913

ISSN

0048-9697

Acceptance Date

2023-12-23

Deposit Date

2023-12-23

Embargo Period

2024-01-31

Funding

This research was conducted whilst in receipt of a PhD studentship funded by the University of Plymouth. We thank Dr. Hein van Kleef (Stichting Bargerveen) for his advice on sampling locations, and critical comments on the manuscript. We are grateful to University of Plymouth technical staff, including Jane Akerman, Alex Fraser, Marie Palmer, Charlotte Crowther and Stanley Butt, for their advice and assistance. We are also grateful to Ethan Quah, Phoebe Marshman, India Brawermann, Rebecca Davies, Harry Mcleod and Simon Cowhig for their assistance in processing field samples. We thank Sergi Sabater and an anonymous reviewer for their constructive feedback, which contributed greatly to the refinement of this manuscript. This research was conducted whilst in receipt of a PhD studentship funded by the University of Plymouth. We thank Dr. Hein van Kleef (Stichting Bargerveen) for his advice on sampling locations, and critical comments on the manuscript. We are grateful to University of Plymouth technical staff, including Jane Akerman, Alex Fraser, Marie Palmer, Charlotte Crowther and Stanley Butt, for their advice and assistance. We are also grateful to Ethan Quah, Phoebe Marshman, India Brawermann, Rebecca Davies, Harry Mcleod and Simon Cowhig for their assistance in processing field samples. We thank Sergi Sabater and an anonymous reviewer for their constructive feedback, which contributed greatly to the refinement of this manuscript.

Keywords

Aquatic ecosystem health, Biological invasion, Ecosystem function, Facilitation, Freshwater biodiversity

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