Using a DNA barcoding approach to facilitate biosecurity: Identifying invasive alien macrophytes traded within the South African aquarium and pond plant industry

Abstract

South Africa's water bodies have been invaded multiple times by various alien macrophytes in the last 200 years and this trend is set to continue – posing a significant threat to the already fragile indigenous aquatic ecosystems and the services they provide. The aquarium and ornamental pond plant industry has been found to serve as a primary pathway for the continued introduction of high-risk taxa. Although regulations like the National Environmental Management: Biodiversity Act (NEM:BA) 10 of 2004 together with some national programmes are currently in place to ensure compliance by the different industry role players, adequate enforcement is hampered by challenges inherent to definitive species identification. In this study, the utility of a DNA barcoding approach to aid in addressing these issues was assessed. An extensive macrophyte core barcode (matK and rbcLa) reference library was compiled and tested to: (i) establish if a “barcode gap” was present, ii) determine the optimised threshold for species delimitation and (iii) assess identification efficiency using different distance based metrices. This reference library was subsequently used to identify plants collected during a survey of ten macrophyte retailer shops in and around the Johannesburg metropolitan area for which DNA barcodes could be generated. Results obtained indicate the presence of considerable interspecific and curbed intraspecific distance between the marker combinations tested and demonstrate high species identification rates. Additionally, multiple alien aquatic plants currently in trade under the following NEM:BA categories were recovered: 1a (invasive species), 1b (invasive species controlled by program) and species prohibited in terms of section 67(1). A surprisingly large number of first-time invasive alien macrophytes not currently on the NEM:BA lists were also identified. The dataset and findings presented in this study have important implications for informing pre-emptive invasive macrophyte management in South Africa e.g. tracking the country's commitments towards achieving the Convention on Biological Diversity's (CBD) Aichi Biodiversity Target 9 (as well as its inheritor post-2020) and providing recommendations for updates to the NEM:BA alien and invasive species lists. The library also presents opportunities for exploring the utility of spin-off applications that rely on robust molecular datasets (e.g. eDNA monitoring).