Marine Biodiversity of Southern Sydney Harbour's Journal

Given that we have entered the winter doldrums for photo submissions, a time when cold weather and/or rain make regular visits to the inky depths of southern Sydney Harbour somewhat less appealing, I thought I'd take this opportunity to provide some updates on our environmental DNA (eDNA) sampling and biodiversity detections in Sydney Harbour.

First, we recently published a scientific paper in the journal of Environmental Research that highlights the biodiversity information that can be gained through what we refer to as tree of life (ToL) metabarcoding based on the sampling of seawater, isolation of eDNA in each sample, and running of >10 genetic tests for things like marine mammals, fish, molluscs, echinoderms, sponges, aquatic plants, and bacteria. In this case, in the winter of 2022, we were able to collect water samples at 34 sites around Sydney Harbour, as far west as Paramatta Weir, but also including sites in southern Sydney Harbour like Camp Cove, Parsley Bay, and adjacent Rose Bay (at the infamous dog beach). Here we found that the number of animal and plant species decreased as you moved away from the mouth of Sydney Harbour into the upper reaches of its tributaries. Interestingly, the differences between sites were not driven by one or a few keystone species, but instead it was based on the effects of many individual taxa coming and going into different parts of the harbour. See the Graphical Abstract above for a simple summary. We see this ToL-metabarcoding approach as an important tool to scientists and community groups alike interested in generating baseline biodiversity data in their neck of the woods (or local waters).

We have also now reached the two-year mark of monthly seawater sampling using eDNA mini kits supplied by our collaborators in New Zealand at Wilderlab. We've now had the opportunity to analyze these data, or at the very least 12 months' worth of data from Camp Cove and Parsley Bay. We also cross-referenced these eDNA detections with citizen science observations on iNaturalist as well as in consultation with a local expert that has been recording his observations at these sites on a near weekly basis for the past 20 years!! See the draft map figure above (thanks Dr Yi-Kai Tea for help with the intricacies of formatting in Adobe Illustrator) that shows our regular eDNA sampling sites alongside some of the important iNaturalist observations in Camp Cove and Parsley Bay. Thanks to our citizen science superstar @eschlogl for sharing photos of seahorses, stingaress, prawns, calamari squid, and so much more at these sites.

Finally, see the draft figure above with a word cloud highlighting differences in the ecological attributes of fish (A,B,C) and macroinvertebrate (D,E,F) species detected in Camp Cove and Parsley Bay unique to eDNA detections (A,D), unique to citizen science records (B,E), or shared between the two datasets (C,F). The Venn diagrams above also depict the overlap in the species identified through eDNA (blue) and citizen science observations (orange), where "N" equals the number of species in each data set. In brief, for the fish, we found that 9.4% of the species were unique to eDNA, 66.1% were unique to citizen science observations, and 24.5% were shared between the data sets. Of the species unique to eDNA, 67.5% were based on a single detection in a single month across both sites. For the macroinvertebrates identified to the species-level (think mussels, oysters, crabs, and prawns as examples), we found that 24.1% species were unique to eDNA, 76.3% were unique to citizen science observations, and 2.9% were shared between the datasets. Of the macroinvertebrate species unique to eDNA, 43.9% were based on a single detection in a single month across both sites. In short, biodiversity data sourced from eDNA and citizen science photo submissions appear to go hand in hand, providing a more complete picture of animals in the marine environment when considered in tandem. Team work makes the dream work!

This journal post was written by project leader and iNaturalist member, Dr Joseph DiBattista.