Oyster and mussel reefs once covered vast areas of the seabed in Port Phillip Bay, and were an important food source for local Indigenous people. However, the reefs were decimated by European settlement and the dredging that came with it.

Patchy groups of oysters and mussels are still found in Port Phillip Bay, and the good news is that trials to restore the reefs are currently underway in two locations.

To help identify other suitable sites for reef restoration, between 2017-2020 ReefWatch monitored shellfish recruitment and survival on settlement plates with the help of its ReefWatchers.

Settlement plates can be anything in the water that larvae in the water column can settle on and survive. In our case, we used small ‘plates’ of PVC.

With settlement plates spread throughout the bay, we hoped to find ‘hot spots’ where large numbers of mussel and oyster larvae settle on them and survive. The ‘hot spots’ could then become sites for the re-establishment of the reefs.

Read more about Oyster Watch in our June 2017 Park Watch article.

This project was in partnership with the Nature Conservancy (TNC) and aimed to help inform future reef restoration efforts. After a pilot stage, we deployed settlement plates at six sites within Port Phillip Bay- at Point Cooke, Albert Park, Rickett’s Point, Mordialloc, Frankston and Blairgowrie. In October 2019 we added an additional 4 monitoring sites- Jawbone (near Williamstown), Mornington, Portarlington and St Leonards (see below for a site map).

Monitoring of settlement units in the field as well as deployment and shellfish counting would not be possible without the valuable contributions of the marine care groups and dive clubs who “adopted” various sites. Volunteers also assisted in data analysis, as well as the construction of settlement units- including piecing together hundreds of settlement plates in the lead up to field deployments.

Clubs and groups involved in OysterWatch activities:

  • Dive2U + Dive2U Dive Alliance
  • Jawbone Marine Sanctuary Care Group
  • Marine Care Ricketts Point
  • Marine Care Point Cooke
  • Diveline
  • Academy of Scuba
  • Australian Diving Instruction
  • Disabled Divers Association

With thanks also to the Albert Park Yachting and Angling Club (APYAC) for their involvement in broader reef restoration efforts, and we thank both APYAC and Blairgowrie Yacht Squadron for use of their facilities during plate deployments and counts.

Our OysterWatchers shared some of their stories in the June 2019 Park Watch. Read them here.

Caption: Citizen scientists about to join their group on a shellfish settlement unit deployment dive at Portarlington, VIC

During Phase 2 of the project (2018-2020) shellfish settlement plates were deployed at sites around the bay and left in the water for approximately 3 months at a time during the oyster breeding season. Over that time, juvenile oysters and mussels settled (recruited) onto the hard PVC plates and began to grow.

Our PVC plates were arranged in a “plate sandwich” set-up which allowed juvenile shellfish to settle on both faces of the individual plates, as well as on the PVC tube that divided them. This arrangement would provide us with information on whether or not the orientation of the settlement surface (facing the surface, facing the sea floor or vertical) had an impact on oyster recruitment/survival. We attached 2 plate sandwiches to a concrete base at 2 different heights to see if position in the water column would also have an effect. 6 of these “settlement units” were deployed at each site.

When it came time to collect the plates our citizen science divers retrieved them, brought them to shore and separated the sandwiches ready for counting. Together we recorded all angasi oysters and blue mussels that could be seen with the naked eye, made a note of whether they were alive or dead, and measured their shell length.

With the 2-year Phase 2 of the OysterWatch project wrapped up, we’re working through the data with TNC to create our hot spot map of oyster (and mussel) recruitment within the bay. In general, there was great variation in oyster recruitment at sites based on location, time of year sampled, and even between years. The hard work of our citizen scientists helped inform marine managers and reef restoration projects as to where oysters are recruiting in higher numbers so they can focus their efforts, as well as laying the groundwork for projects at other places around Australia. Here is the overview of what our OysterWatchers found:


  • Oyster numbers varied greatly between sites and sampling periods. Frankston recorded the highest total number of oysters throughout the project (this includes data from 2020, where sampling from the Frankston site did not occur), followed by Ricketts Point and then Blairgowrie. Oysters were also recorded at Mordialloc, Kerferd Rd and Pt Cooke and Jawbone, but in lower numbers. Portarlington and St Leonards recorded no oysters, but along with Jawbone and Mornington these sites were only sampled in Round 1 of 2020, which appeared to be a much weaker spawning event for this species.
  • Far greater numbers of oysters were recorded on settlement plates during Round 1 (October-Jan) than during Round 2 (Jan-April) sampling periods at most sites.
  • Annual variation was also significant- a total of 65 oysters were recorded across all sites in the bay for Round 1 sampling in 2020, compared to 611 in 2019 and 545 in 2018 (and despite increasing numbers of participating sites from 2018-2020).
  • More oysters were recorded facing towards the seabed than towards the surface, or on the vertical PVC divider positioned between plates. Height of plate (high or low) on settlement unit did not appear to have a substantial effect on oyster settlement
  • Note that this data is for our angasi oysters only. Mussel data and further analysis to come!

On Monday 14 September 2020 ReefWatch’s Nicole joined TNC’s Operations Manager Simon to share the results and highlights of Phase 2 of the OysterWatch project, as well as how the data our citizen scientists collected is informing reef conservation efforts in Port Phillip. You can watch the full session below.