Where DNA Meets the Divers
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Southern Sydney Harbour: A Hidden Hotspot of Marine Life Revealed by Environmental DNA
What if a single bottle of seawater could tell us what animals and plants eat, sleep, breath, swim, and sway beneath the ocean surface? That’s exactly what researchers set out to explore in southern Sydney Harbour, using environmental DNA (eDNA) - tiny traces of genetic material left behind by marine organisms in the water. By collecting monthly seawater samples for an entire year between September 2022 and August 2023 at Camp Cove and Parsley Bay and then sequencing the DNA in those samples, the researchers uncovered a remarkable snapshot of marine life in southern Sydney Harbour, detecting everything from bacteria and algae to fish, jellyfish, crustaceans, and other marine invertebrates. The genetic results reinforce what many local naturalists already suspected: southern Sydney Harbour, including Parsley Bay, is an extraordinary reservoir of biodiversity.
A Living, Breathing, and Dynamic Ecosystem That Never Stands Still
One of the most exciting discoveries was just how dynamic the genetically characterised biodiversity was through time. Camp Cove and Parsley Bay was richest during summer and autumn, when DNA signatures from a wide variety of organisms flooded the water column. In contrast, winter brought noticeably fewer eDNA detections, especially at low tide. Even though Camp Cove and Parsley Bay are located only about a kilometre apart, they each showed distinct biological communities that changed with the seasons. These findings suggest that southern Sydney Harbour is not a static ecosystem but a living, ever shifting mosaic of available habitat and species responding to their environmental conditions throughout the year.
Iconic Species, Tropical Visitors, and Microscopic Wonders
The study also highlighted the detection of species with local conservation and fisheries values, including the IUCN Endangered White’s Seahorse (Hippocampus whitei), Southern Calamari Squid (Sepioteuthis australis), Eastern King Prawn (Melicertus plebejus), and the IUCN Near Threatened Kapala Stingaree (Urolophus kapalensis). The harbour also continues to host tropical and subtropical visitors arriving via the East Australian Current, reflecting Sydney’s unique position where temperate and warmer-water species co-mingle. Together, these eDNA detections paint a picture of an estuary that supports everything from microscopic organisms to apex predators.
The Power of Combining Local Ecological Knowledge with New Technologies
Importantly, the story of southern Sydney Harbour’s biodiversity could not be told through DNA alone. The researchers combined eDNA results with more than a century of museum collections, thousands of citizen-science observations at these two sites, and decades of local ecological knowledge in the form of regular underwater sightings inventoried by our co-author, long-serving Woollahra Bushcare volunteer, and Local Hero (awarded November 2025) Robert Hitchen. Each source of data contributed unique pieces to the puzzle, with many species detected by only one method. Some appeared only in museum records. Others surfaced exclusively through eDNA. Others still only become apparent with the sharp eyes of citizen scientists armed with underwater cameras. Interestingly, one citizen scientist photographed the Orangespotted Glidergoby Valenciennea puellaris in Parsley Bay, which based on this new record extended its range poleward approximately 1200 km from One Tree Island on the Great Barrier Reef in Queensland (https://www.inaturalist.org/observations/153898773). This synthesis of different data sources therefore demonstrates the enormous value of naturalists, photographers, divers, and citizen scientists whose observations help reveal species that might otherwise go unnoticed. In fact, these contributions are more than just supplementary - they are irreplaceable.
There is Still so Much More to Discover
Perhaps the biggest takeaway is that there is still far more to discover. Even after a year of monthly sampling, the biodiversity inventory never reached a plateau, suggesting many species remain undetected. Southern Sydney Harbour continues to surprise researchers with its richness and complexity, underscoring its importance as a biodiversity stronghold within one of the world's great urban harbours. As new tools like eDNA are combined with traditional observations and community science, we are gaining an unprecedented view of the life thriving beneath Sydney’s busy waterfront — and a powerful reminder of why protecting supporting marine habitat matters.
The Bigger Picture
This study would not, and could not, have been completed without the help of Nicole McMahon, Andrea Alembakis, Oliver Strewe, Xanthe, and the countless community members that helped with eDNA sampling. This study was also dependent on the efforts of Atlas of Living Australia in providing Open Access biodiversity data, as well as natural history museum staff, governmental scientists, and citizen scientists that contributed their time, efforts, and expertise to this work.
The conservation implications from these new and permanent records of biodiversity generated in this study cannot be overstated. Earth to Sea Guardians depends on these types of biodiversity data to build a scientific portfolio for Parsley Bay that highlights its importance in our marine environment. Earth to Sea Guardians are also tirelessly working towards protecting Parsley Bay in the form of a no-take aquatic reserve, so that generations to come can enjoy it as it should be. This proposal for protection can be viewed on our main webpage and the movement supported by signing the petition for protection.
Further Reading
This comprehensive study on southern Sydney Harbour's marine biodiversity was led by Dr Joseph DiBattista and a dedicated team of collaborators, documenting dynamic seasonal shifts in this marine biodiversity through eDNA metabarcoding alongside historical museum data and citizen science observations via iNaturalist, and supplemented by local ecological knowledge amassed over the decades by our co-author Robert Hitchen. The research provides an important case study for tracking biological communities in highly urbanised estuaries and evaluating how seasonality and environmental conditions influence species detections.
The authors acknowledged funding and project support provided through the Australian Museum, sponsorship from Blue World through the Valerie Taylor Ocean Prizes, which together initiated their long-term monthly sampling across Camp Cove and Parsley Bay.
Even more exciting is through past support from the Wettenhall Environment Trust, the Woollahra Council - Community and Cultural Grants Program, and now ongoing support from the Minderoo Foundation's OceanOmics Program, monthly eDNA sampling at Parsley Bay is fast approaching four years and will continue for the foreseeable future. This makes this research program one of the longest running coastal eDNA time series in the world!
Read Full Open Access Scientific Paper Here:
https://www.sciencedirect.com/science/article/pii/S2352485526004500
Original Research Article
DiBattista, J.D., Fowler, A.M., Harasti, D., Hitchen, R., McMahon, N., and Wilkinson, S. (2026) Temporal variation in environmental DNA detections within an urban estuary. Regional Studies in Marine Science, 101, 105195.
This blog post was written by Dr Joseph DiBattista from Earth to Sea Guardians.