Investigating the decline and future of the threatened bladderwort Utricularia australis in New Zealand

Author: Davies-Colley, Taylor

Date: 2021

Publisher: University of Otago

Type: Thesis

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Around the globe biodiversity has been at threat due to changes in ecosystems, of which most are anthropogenic in origin. One area of biodiversity that has been impacted gravely is the flora and fauna of small lakes and wetlands, as these areas have suffered large amounts of historical modification, and are at threat from further being modified negatively in the future, by agriculture, forestry and invasive species. Utricularia australis is a species of free floating aquatic bladderwort that inhabits such areas and has therefor suffered a significant decline of greater than 70% in the last 10 years making this species now nationally critical in threat status. In Northland of 22 lakes it used to inhabit that are regularly surveyed it now only persists in 3. To protect species like U. australis we must understand how these changes to the environment are effecting the species, what factors are the most influential and at what level of interaction may they cause harm or loss. The protection of this species in New Zealand and globally is also shadowed by taxonomic uncertainty and recruitment issues. This thesis investigates firstly the phylogenetic relationship between New Zealand populations of U. australis and those in Australia as well as Europe. Using ITS markers from samples taken in New Zealand and sequences provided from other countries it was possible to determine that New Zealand populations of U. australis were indeed within that taxon which had been historically disputed. Using historical records of lake vegetation and water quality, analysis were carried out to determine the relative importance of each water quality factor on the presence or absence of U. australis in Northland lakes. This investigation was made difficult by the rapid loss of U. australis from study lakes, however, a negative relationship between Trophic Level Index and the presence of U. australis was observed despite no factors showing significant impacts alone. Relationships between land use and presence were significant with U. australis now only found in lakes with indigenous or native forested catchments. Aerial images matched with time also highlighted the risk between sedimentation from logging events and loss of U. australis in lake Te Kahika. A threat that needs to be further investigated an mitigated in the future. Species distribution modelling techniques allowed the prediction of the total range of the invasive Utricularia gibba could inhabit in New Zealand based of climate information from its Australian range. A greater range was predicted that what is currently inhabited including populations of U. australis that have been unaffected by the species. Modelling of future climate showed the species to have a small increase in potential range suitability in areas with increased temperature. Summarising the information in the prior chapters conservation recommendations have been made to prevent further decline or loss of the species, as well as the environments they live in. These include further research into potential low genetic diversity and genetic caused recruitment failure, the interactions between U. gibba and U. australis, and he management of land around lakes to prevent degradation. Further recommendations include, strategic riparian areas to protect lakes and staggered logging to prevent mass sedimentation events that may cause loss. The information presented is a useful beginning into understanding this unique species in New Zealand and trying to protect it before it is lost.

Subjects: New Zealand, Plants, Utricularia, Weed, Ecology, Carnivorous Plants, Utricularia australis

Citation: ["Davies-Colley, T. (2021). Investigating the decline and future of the threatened bladderwort Utricularia australis in New Zealand (Thesis, Master of Science). University of Otago. Retrieved from"]

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