Implications for selected indigenous fauna of Tiritiri Matangi of the establishment of Austropuccinia psidii (G. Winter) Beenken (myrtle rust) in northern New Zealand

Abstract

Myrtle rust (Austropuccinia psidii (G. Winter) Beenken) was detected on the New Zealand mainland in May 2017. Myrtle rust was first described in Brazil in 1998, and since then has spread throughout the Americas, to Asia, Africa, the Pacific islands, and most recently to Australia, causing a global pandemic. A. psidii is a pathogen of the Myrtaceae family, and attacks young leaves, shoots, stems and flowers. Given overseas experience with the pathogen, a wide range of host species in New Zealand are expected to have the potential to be infected. In New Zealand, the optimal conditions for myrtle rust are predicted to be confined to mainly coastal and the northern areas of the North Island. In these areas, Myrtaceae species, principally pōhutukawa Metrosideros excelsa, kānuka Kunzea robusta and mānuka Leptospermum scoparium are common, and may dominate plant communities.

The aim of this review is to consider the potential longer-term impact of myrtle rust, with a focus on the flow-on effect to indigenous New Zealand fauna, particularly the nectarivorous species that use myrtaceous flowers as a food source. This potential is explored through a case study of Tiritiri Matangi Island, an ecological restoration project in the Hauraki Gulf, northern New Zealand. Although any degradation or loss of the Myrtaceae will have long-term and potentially devastating impacts on the myrtaceous habitats and allied fauna, we suggest that niche flexibility associated with much of the New Zealand fauna bodes well for such future environmental challenges. Fauna with an obligate relationship with Myrtaceae, however, may be at greatest risk from the pathogen’s establishment. Management options are suggested to mitigate the impact of myrtle rust on nectarivorous fauna.