Dr Jaret Bilewitch1, Amber Brooks1, Lisa Smith1, Dr. Andrew Swales2
1NIWA, Wellington, New Zealand, 2NIWA, Hamilton, New Zealand
Biography:
Jaret Bilewitch is a molecular marine biologist with integrative experience in molecular systematics, population genetics, evolutionary biology, genomics and marine ecology. He specialises in developing molecular biological tools for application in environmental sciences, including conservation biology, biosecurity, biodiversity, oceanography, and fisheries sciences.
Abstract:
The high intensity and duration of rainfall during Cyclone Gabrielle (February 2023) resulted in extensive soil erosion and flood-plain sedimentation in the Te Matau-a-Māui/Hawke’s Bay and Tairāwhiti/Gisborne regions. Large quantities of terrigenous sediment and forestry slash were subsequently discharged into the coastal marine environment. Fisheries New Zealand commissioned NIWA to undertake an initial investigation to identify the contributions of major rivers to marine sedimentation, as part of a wider evaluation of the impacts of Cyclone Gabrielle on marine habitats and the fisheries they support.
We explored the application of eDNA as a biomarker for characterising and tracing sediment transport, as a complement to well-established isotopic tracing and mixture methods implemented by NIWA. The taxonomic composition of sediments collected from seven river mouths and nearby offshore transects was determined using eDNA metabarcoding targeting vascular plants. Over 900 unique eDNA signatures were detected, identified as 248 taxa of willows, poplars, beech, kānuka, ferns, and a variety of shrubs and flowering plants. Low eDNA abundance for pine trees was observed in river mouth and offshore sediments, resulting from a gap in reference databases and potentially low eDNA availability. Taxonomic heterogeneity within sampling areas plus a lack of distinctiveness between river mouths obscured linkages between marine transects and river mouths in comparisons of individual taxa and community-level diversity metrics. Thus, while eDNA was successful in characterising specific terrestrial inputs to sediment deposits, its application as a tracing method was hindered by a lack of catchment- and land-use-specific references and an established analytical framework.