Port Phillip Bay Seafloor Integrity Project (2021-2024)

• Action 6.1: Monitor indicator species and key habitats at priority locations.
• Action 6.2: Improve understanding of ecological processes, threats and pressures.
• Action 6.3: Improve the overall extent and condition of the Bay’s natural ecosystems.

• Action 3.1: Effectively maintain existing stormwater infrastructure and programs to mitigate loads to the Bay, or secure via equivalent means.
• Action 3.2: Prevent increases in nutrient loads from wastewater systems and, where practicable, reduce loads of other pollutants.
• Action 3.3: Ensure all urban and rural land use effectively controls impacts from stormwater and runoff, and that controls are in place to manage increases in loads.

To study the physical and chemical sediment properties:

• Forty-five sediment samples have been collected across Port Phillip Bay using a Ponar Grab.
• Samples were analysed to characterise grain size to understand bioavailability and toxicity of contaminants.
• Samples were analysed for a presence of inorganic and organic compounds and nutrients (for example pesticides, metals and emerging contaminants such as PFAS).

Biogeochemical processes play a critical role in regulating the impacts of nutrient loads into Port Phillip Bay that influence benthic ecosystem community composition and production. Processes were studied at the sediment-water interface including respiration, primary production, and denitrification. Fathom Pacific in collaboration with the Centre for Coastal Biogeochemistry (Southern Cross University) investigated:

• Diver hand cores were collected and analysed for Total Organic Carbon and Pigments at 42 sites.
• Sediment incubation cores were collected from a total of 12 sites of muddy sediments and analysed in a laboratory to understand gross productivity of sediments and measure microphytobenthos abundance using chlorophyll-a and phaeophytin.
• Benthic chamber cores were installed in-situ and monitored a total of 4 sites comprising of sandy sediments.

Underwater imaging surveys of the benthic ecosystem, using Autonomous Underwater Vehicle (AUV) technology, were undertaken to inform the identification of biological indicators of seafloor integrity and led by the Australian Centre for Field Robotics:

• AUV surveys were completed at 35 sites, each transect being 500m long and following a broad or dense grid design.
• Good imagery has been collected for 72 km of survey distance and consists of 410,000 images converted to orthomosaics.
• Image-based morphospecies identification, abundance scoring have been annotated using the software platform SQUIDLE+.
• ROV surveys are planned for 2024 and will be conducted by the Fathom Pacific team.

To investigate how contaminated sediments interact with other elements of the benthic ecosystem in the Bay, Fathom Pacific has partnered with the School of Agriculture, Biomedicine and Environment at La Trobe University to undertake ecotoxicological studies. Ecotoxicological analysis allows the investigation of bioavailability of contaminants to marine fauna and bioaccumulation across the food web. Studying the concentration of harmful contaminants in marine species is key to understanding whether pollutants found in sediments and water can be transferred to marine organisms.

• Fish and invertebrates were collected across 10 different zones, 7 represent impacted sites and 3 from control areas.
• Fish species include sand flathead and southern fiddler ray.
• Invertebrate species include Pyura spp., scallop, sea star, European fan worm.
• Tissues (muscle, liver, blood, gonads, mucous) and biomarkers were analysed.

To facilitate data management for the project, Fathom Pacific have engaged Nordinson Studios. They have also developed a web portal to view project data stored in the qCore database. This provides visibility on completed field activities and accessibility to project data.