Impacts of a putative invasive ascidian on rocky shore communities

• Published in: Marine environmental research Vol. 168; p. 105308
• Main Authors: Atalah, Javier, Fletcher, Lauren M., Forrest, Barrie M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-06-2021; Elsevier BV
• Subjects: Ascidian; Body condition; Coastal ecology; Community development; Density dependence; Geographical distribution; Impacts; Indigenous species; Intertidal community dynamics; Introduced species; Literature reviews; Marine invertebrates; Mollusks; Mussels; Native organisms; New Zealand; Non-indigenous species; Physiological effects; Pyura doppelgangera; Recruitment; Recruitment (fisheries); Rocky shores; Tunicate; New Zealand; Impacts; Ascidian; Non-indigenous species; Pyura doppelgangera; Tunicate; Intertidal community dynamics
• ISSN: 0141-1136; 1879-0291
• DOI: 10.1016/j.marenvres.2021.105308

The number and distribution of non-indigenous species in coastal habitats is increasing. Our ability to prioritise the management of this threat is limited by our understanding of their impacts. We investigated the density dependent effects of the non-indigenous solitary ascidian Pyura doppelgangera on native mussels and rocky shore communities in northern New Zealand. Minimal recruitment of P. doppelgangera was recorded during a 1.5-year experiment. Mussels showed no sign of overgrowth or spatial competition with P. doppelgangera, and their physiological condition was not impacted. We found marginal effects of the ascidian on community development, associated with small increases in diversity. We concluded that P. doppelgangera is not an aggressive competitor nor a threat to native communities, as previously thought, and that it has a very limited natural recruitment and spread potential. Reports from local Māori and a literature review suggest that P. doppelgangera has been present in the area for longer than previously thought, raising questions about its ‘introduction’ status and its current designation as a pest.
•Minimal recruitment of Pyura doppelgangera was recorded over 1.5 years.•Mussels showed no sign of overgrowth or competition, and their condition was not impacted.•We found marginal effects of the ascidian on community development.•We concluded that the ascidian is not a threat to native communities.•We raised questions about its introduction status and its current designation as a pest.