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Seawater Sampling and Collection
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Examining Marine Assemblages Across an Inverse Salinity Gradient
Kirsty E Richards1, Simon Jarman1, Benjamin J Saunders1
1School of Molecular and Life Sciences, Curtin University, Perth, Western Australia, Australia.
Molecular Ecology
|March 27, 2026
Summary
Marine biodiversity significantly declined with increasing salinity in Shark Bay, Australia. Despite reduced diversity and altered community composition, essential ecological processes persisted across the inverse salinity gradient.
Area of Science:
- Marine ecology
- Environmental DNA (eDNA) analysis
- Biogeochemistry
Background:
- Salinity gradients act as ecological filters, limiting species survival above 50 practical salinity units (PSUs).
- Shark Bay, Western Australia, features a remote hypersaline coastal embayment with an inverse salinity gradient.
Purpose of the Study:
- To investigate the impact of an inverse salinity gradient on marine community diversity and composition.
- To assess the utility of eDNA metabarcoding for analyzing marine assemblages across environmental gradients.
Main Methods:
- Utilized 16S (fish), 18S, and 16S (Bacteria) eDNA metabarcoding assays.
- Analyzed genetic sequences from 220 surface water and 216 benthic roller samples across 44 sites.
- Covered a salinity range from 40.1 PSU to 76.0 PSU.
Main Results:
- A total of 24,011,345 eDNA sequencing reads and 5575 operational taxonomic units (OTUs) were detected.
- Marine community diversity (Families and OTUs) decreased significantly with increasing salinity, particularly between 50-60 PSU.
- While taxonomic composition shifted, the relative proportion of major Phyla remained stable, suggesting maintained ecological processes.
Conclusions:
- Increasing salinity dramatically reduces marine biodiversity and alters community structure in Shark Bay.
- Despite biodiversity loss, core ecological functions may be preserved across the gradient.
- eDNA metabarcoding is a valuable tool for broad-scale marine community assessment in remote, challenging environments.
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