Using eDNA to assess how estuarine fish communities respond to consecutive extreme events of drought, bushfire, and post-fire flood

In the face of climate change, it is vital to gather baseline data to improve our limited understanding of the diversity and distribution of estuarine fish communities to allow us to track changes in community composition in response to extreme weather events such as drought, fire, and flood. Historical environmental DNA (eDNA) samples were collected weekly by NSW Oyster Farmers over a 24-month period (2018-2020), resulting in the largest fish survey in NSW estuaries using eDNA and fish metabarcoding. This pilot study examined how the composition of fish assemblages in three estuaries in NSW including the Hastings River, Shoalhaven River and Wagonga Inlet were impacted by consecutive extreme weather events of 2018-2020, such as the hottest and driest drought on record, the black summer bush fires and the first post-fire rain events. Results provide critical baseline information surrounding estuarine fish community composition, including changes in composition throughout these events. Findings will inform the expansion and design of long-term biomonitoring programs in estuaries throughout NSW, while contributing to the on-ground conservation and management practices for estuaries in preparation for future extreme weather events.