Dr Matthew Nimbs1, Dr Mirjam van der Mheen2, Andrew Benson1, Associate Professor Melinda Coleman1
1Fisheries Research, NSW Department Of Primary Industries And Regional Development, Coffs Harbour , Australia, 2University of Western Australia, Perth, Australia
Biography:
Matt Nimbs trained as an invertebrate taxonomist and is now a research scientist and geneticist working in the climate change space with the NSW DPIRD marine ecosystems unit. He specialises in climate change genetics primarily associated with major habitat forming species within NSW waters. His major outputs include widespread genomic analyses of golden kelp and bull kelp, Posidonia seagrass and culturally important Turban snail fisheries.
Abstract:
Kelp forests dominate subtidal rocky reefs across temperate and subtropical Australia and are increasingly recognised as significant contributors to marine blue carbon budgets. On the northern New South Wales coast, Ecklonia radiata forms the sole large laminarian community and is a major source of dislodged detrital biomass, yet the fate of this material across the continental shelf and its sequestration into sediment remains poorly resolved. We used eDNA metabarcoding of paired sediment and water column samples collected along four cross-shelf depth-gradient transects (50–300 m) to test whether kelp eDNA distribution reflects modelled patterns of offshore kelp particle transport. Kelp eDNA was detected in 21 of 45 samples (46.7%) across all four study areas and both modelled particle transport corridor classes. Detection probability declined significantly with depth, while transport corridor, sample type, and their interaction were not significant predictors of detection. Consistent kelp signals were recorded in shallow sediments at 50–100 m depth at sites within both low and high transport corridors, indicating that proximal sediment accumulation may be the dominant depositional mode for kelp-derived carbon, with corridor-mediated offshore export contributing a smaller, depth-attenuated signal. These findings reframe the spatial footprint of kelp blue carbon deposition as concentrated in nearshore-to-mid-shelf sediments immediately adjacent to source reefs, with implications for management: the source kelp forest and the adjacent proximal sediment field function as a coupled unit whose conservation is a prerequisite for sustained macroalgal carbon sequestration on the northern NSW coast.