Assessment of the risks to Norwegian biodiversity from aquarium and garden pond plants
Aquatic invasive alien plants can have high negative impacts in areas they invade. Impacts include blanketing monocultures which can outcompete native plant species and associated fauna, economic impacts by degrading land and blocking drainage channels and impacts on ecosystem services including cultural and regulating services. The Norwegian Environment Agency commissioned a study on the assessment of risks to Norwegian biodiversity from the import and keeping of aquarium and garden pond plants. For the assessment, aquatic species were preliminary screened into 1 of 3 categories based on their area of occurrence and climatic preferences. Those species in category 1 are naturally occurring in tropical climates – these species were further assessed to see if they can survive naturally below 5 OC. Category 2 taxa include those naturally occurring in temperate and continental climates – these species were individually risk assessed (see table 1 for an output using a modified two-stage Non-native Species Application-based Risk Analysis process). Species in category 3 were taxa occurring naturally in Norway and these species were assessed as a group to evaluate the risk of transferring genetic material to local populations. See the full report for the list of category 1 and 3 species. For those species where a full risk analysis was conducted (see table 1), Crassula helmsii and Myriophyllum heterophyllum (both EPPO A2 species) were highlighted as two species posing a high risk to biodiversity in Norway.
Table 1. Aquatic plant species subjected to full risk assessments. Confidence levels in brackets equal, L: Low, M: Medium, H: High). Mod represents moderately. Potamogeton species were risk assessed together and include: P. epihydrus, P. nodosus, schweinfurthii, P. wrightii.
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Species
|
Entry
|
Establishment
|
Spread
|
Impacts
|
Overall
|
|
Ceratophyllum submersum
|
Very likely (H)
|
Likely (H)
|
Very slowly (H)
|
Minimal (H)
|
Low (H)
|
|
Crassula helmsii
|
Likely (M)
|
Mod likely (L)
|
Rapid (M)
|
Major (M)
|
High (M)
|
|
Egeria densa
|
Likely (M)
|
Mod likely (L)
|
Slowly (M)
|
Mod (M)
|
Mod (M)
|
|
Eleocharis vivipara
|
Likely (M)
|
Unlikely (L)
|
Slowly (M)
|
Minimal (L)
|
Low (M)
|
|
Hydrilla verticillata
|
Likely (M)
|
Mod likely (L)
|
Mod fast (M)
|
Mod (M)
|
Mod (M)
|
|
Lagarosiphon major
|
Likely (M)
|
Mod likely (L)
|
Slowly (M)
|
Mod (M)
|
Mod (M)
|
|
Lemna gibba
|
Likely (M)
|
Mod likely (M)
|
Mod fast (M)
|
Minor (M)
|
Mod (M)
|
|
Myriophyllum aquaticum
|
Very likely (H)
|
Likely (H)
|
Mod fast (H)
|
Mod (H)
|
Mod (H)
|
|
Myriophyllum heterophyllum
|
Very likely (H)
|
Likely (H)
|
Rapidly (H)
|
Major (H)
|
High (H)
|
|
Myriophyllum quitense
|
Likely (H)
|
Unlikely (M)
|
Slowly (M)
|
Minimal (M)
|
Low (M)
|
|
Najas guadalupensis
|
Very likely (M)
|
Mod likely (L)
|
Slowly (L)
|
Minor (L)
|
Low (L)
|
|
Najas minor
|
Mod likely (M)
|
Likely (M)
|
Mod fast (M)
|
Mod (M)
|
Mod (M)
|
|
Potamogeton spp.
|
Unlikely (M)
|
Unlikely (M)
|
Slowly (L)
|
Minimal (M)
|
Low (M)
|
|
Salvinia natans
|
Likely (H)
|
Unlikely (H)
|
Very slowly (H)
|
Minimal (H)
|
Low (H)
|
|
Trapa natans
|
Very likely (M)
|
Unlikely (L)
|
Mod fast (L)
|
Mod (L)
|
Mod (M)
|
|
Vallisneria spiralis
|
Likely (H)
|
Unlikely (M)
|
Very slowly (L)
|
Minor (M)
|
Low (M)
|
|
Wolffia arrhiza
|
Mod likely (L)
|
Mod likely (L)
|
Mod fast (L)
|
Minor (L)
|
Minor (M)
|
Sources
VKM (2016) Assessment of the risks to Norwegian biodiversity from the import and keeping of aquarium and garden pond plants. Scientific Opinion on the alien organisms and trade in endangered species of the Norwegian Scientific Committee for Food Safety ISBN: 978-82-8259-240-6. Oslo, Norway.