Recommended citation: Global Invasive Species Database (2025) Species profile: Cygnus atratus. Downloaded from http://iucngisd.org/gisd/speciesname/Cygnus+atratus on 05-02-2025.
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MO
Cygnus atratus
Date assessed
2021-10-04
Year published
2022
Eicat category
MO (Moderate)
Justification for EICAT assessment
In New Zealand the Black Swan is the only large grazer of intertidal seagrass. At sites of intense grazing (annual removal of 19-20% of the average seagrass biomass), substantial decline (43-69%) in plant biomass in the subsequent growing season was observed (Zostera muelleri) (Dos Santos et al. 2012).
Confidence rating
High
Mechanism(s) of maximum impact
Grazing/herbivory/browsing
Countries of most severe impact
New Zealand
Description of impacts
The Black Swan feeds on native plant species, causing the decline of a native seagrass in New Zealand. It also hybridizes with native swan species.
Assessor
Thomas Evans; Tom Allmert
Contributors
Reviewers
EICAT authority
Recommended citation
Thomas Evans, Tom Allmert (2025). Cygnus atratus. IUCN Environmental Impact Classification for Alien Taxa (EICAT).