Dr Katrina West1, Tim O'Hara2, John Pogonoski1, Sahan Jayasinghe1, Stephanie Joyce3, Tiffany Sih4, Yi-Kai Tea5,6, Sharon Appleyard1, Bruce Deagle1
1CSIRO, , Australia, 2Museums Victoria Research Institute, , Australia, 3University of Tasmania, , Australia, 4Oceans Institute, The University of Western Australia, , Australia, 5Ichthyology, Australian Museum Research Institute, , Australia, 6School of Life and Environmental Sciences, University of Sydney, , Australia
Biography:
Dr Katrina West is a Research Scientist at CSIRO specialising in eDNA-based technology for marine species monitoring. She completed her PhD at Curtin University (2016–2020), applying eDNA metabarcoding in novel environments such as aquatic caves and across large spatial scales in Australia's Indian Ocean region to identify biogeographic breaks in marine biodiversity. As a CSIRO Postdoctoral Fellow (2021–2024) with the Australian National Fish Collection, she conducted large-scale eDNA surveys of marine fishes and sharks across coastal and offshore ecosystems. Katrina now works within CSIRO's Environomics Team, developing new approaches for eDNA enrichment, quantification and ecological modelling.
Abstract:
Deep offshore ecosystems remain among the least biologically characterised regions of the global ocean reflecting the logistical challenges of sampling at depth. Here, we use environmental DNA (eDNA) metabarcoding to characterise fish richness and community composition across the Christmas Island Seamount Province (CHRISP) in the eastern Indian Ocean. Seawater samples were collected using a CTD from 69 sites across four depth strata spanning the water column to the seafloor (maximum depth: 4,916 m) during two RV Investigator voyages (IN2021_V04; IN2022_V08) in July 2021 and October 2022, respectively. A total of 320 fish taxa were detected, including 150 species-level, 142 genus-level and 28 family-level assignments. Assemblages were dominated by mesopelagic and bathydemersal fishes but also included epipelagic taxa, with eDNA detections largely adhering to presently known species depth distributions. Eighty taxa (25%) represent new occurrence records for the CHRISP region, including 27 independently validated by synchronous trawl surveys. Fish richness declined with increasing pressure/depth but peaked at intermediate depths (~500 m), driven by elevated pelagic midwater diversity. Community composition showed strong vertical structuring, with progressive replacement of epipelagic taxa by meso- and bathypelagic species with depth, and a transition in seafloor assemblages from shallow reef- and shelf-associated fishes to deeper bathydemersal taxa. Longitudinal variation in richness and composition was also evident across the region and at different depth layers, however, was primarily influenced by proximity to overlying, shallow seamount topography and vertical connectivity, with limited evidence for any strong benthic biogeographic differentiation across the CHRISP region.