Up until the turn of the last century, Moreton Bay supported magnificent intertidal and subtidal shellfish beds which had always been a valuable food and cultural resource for Traditional Owners. The oyster industry was certainly the foremost industry carried on in early days of Moreton Bay’s history and local development. The oysters were used for a variety of purposes – not just eating. Queensland’s early roads were made shell from midden heaps and the live and dead oysters were thrown into the lime burners for cement. It did not take long for overharvesting, disease and water pollution to deplete the shellfish stocks to the point where they are now functionally extinct in Pumicestone Passage.
In 2015, Healthy Land and Water launched the Pumicestone Shellfish Habitat Restoration Project alongside Traditional Owners, community and recreational fishing groups, a local oyster farmer, Moreton Bay Regional Council, Unitywater, and the University of the Sunshine Coast (USC) to work toward restoring the Pumicestone Passage’s lost shellfish habitats to enhance fish stocks, marine biodiversity, and ultimately improve water quality in the Pumicestone Passage.
After 1.5 years, all relevant approvals were granted for the first sub-tidal shellfish habitat to be installed in Queensland. Several types of structures were deployed at 3 – 5 metres depth within a hectare area off Kakadu Beach, Bribie Island in December 2017. These were augmented with two larger patch reefs in 2018 and again with two larger patch reefs in 2019.
Researchers from the University of the Sunshine Coast are monitoring fish abundance and diversity near the site and across the seascape, and the results are compelling. The most recent fish monitoring report from June 2020 showed the site contains a fish assemblage that is 3.8 times more speciose. In addition, some 16.4 times more harvestable fish and 10.7 times more fish abundance was reported than in pre-installation surveys The report shows that the abundance of fish at the habitat restoration site is so high that differences in the abundance and diversity of fish congregating around individual reef units, and therefore their contribution towards the broader fish assemblage patterns, is difficult to distinguish statistically.
The June 2020 Report suggests that it is likely the reef restoration action has increased the overall carrying capacity of the lower Pumicestone Passage, and therefore is unlikely to have functioned simply as a fish attracting device. This work is preliminary at this stage, however, will be confirmed following additional analyses that will be described in the final report. OzFish Unlimited has also been undertaking invertebrate studies which have shown that reef-forming shellfish continue to recruit (up to 152 spat/100 shell) and survive (up to 82% survival rate) after two years if kept uncovered at a height of 50 centimetres above the substrate.
Healthy Land and Water has now been informed that the Marine Parks research permit has been extended beyond the original expiry date of December 2020.
Over the course of the three-year project, the funding has been provided by Pumicestone Passage Fish Restocking Association, National Landcare Program, Moreton Bay Regional Council, Boating Camping Fishing (BCF) through OzFish Unlimited, and Unitywater, with significant in-kind from OzFish volunteers in their oyster gardening project, shell recycling and invertebrate monitoring.
The purpose of the Pumicestone Passage Shellfish Reef Restoration project is to restore shellfish reef populations for the benefit of the Moreton Bay ecosystem and the community.
Not only are shellfish a vital part of Indigenous cultural heritage, but they are also an incredibly important cog in marine ecosystems. Shellfish are fondly known as the “kidneys of the coast” due to their natural filtration properties and for their ability to improve water clarity by drawing in particles and distributing them to the seafloor.
Once grown, each shellfish can filter up to 100 litres of water a day, helping to create an environment that allows many other plant and animal species in estuaries and coastal bays to thrive.
If the method used in the Pumicestone Passage restoration project proves to be successful, and self-sustaining subtidal oyster reefs are established, the data and outcomes can be used to justify and inform larger-scale restoration efforts in other areas of Moreton Bay.
After years of research, the project team settled on a plan to install artificial shellfish reefs in a Pumicestone Passage trial area. The artificial reefs are designed to provide an attachment point for shellfish, and the embedded recycled shells act as a food-source for shellfish larvae as they mature. As shellfish populations expand, they support the growth of important fish species, enhance marine biodiversity and ultimately improve water quality in the Moreton Bay region.
In December 2017, the first artificial shellfish reefs were installed within a one-hectare site offshore of Kakudu Beach at Bribie Island. The trial area is located within the Moreton Bay Marine Park, and the artificial reefs were installed in an area with a depth range of between 2.5 and 5.2 metres.
Three different structures were embedded underwater, including patch reefs of shell weighted with reef balls, steel cages full of recycled shell and an Australian-first biodegradable potato starch matrix that was developed in the Netherlands by Bureau Waardenburg. A combination of recycled and live shells were used within the structures.
In December 2018, a second array of artificial reefs were installed within the test area. The new reefs, made up of live and recycled shells collected by OzFish Unlimited volunteers at the Ningi Transfer Station, are designed to increase the process of reef adhesion and productivity.
The project is being monitored by University of the Sunshine Coast marine science team.
Since the first stage of reefs were installed in December 2017, initial results look promising.
A University of Sunshine Coast (USC) study released in late 2018 found fish abundance, species richness and harvestable fish numbers had doubled since the installation. The potato starch matrix reefs appear to be the most successful installation so far, with the study finding the potato starch reefs are consistently surrounded by a higher average diversity and abundance of fish when compared to nearby control sites.
The study found evidence of prolific colonisation by corraline algae and soft corals, which helped cement the loose shells together into a reef formation. Most excitingly, fish distributions across lower Pumicestone Passage have expanded slightly since the installations, and some species have moved closer to the reef areas.
However, much more data is needed before an accurate conclusion can be formed regarding the success of the artificial reef installations. Ongoing research by USC is analysing the broad effects of the trial and taking into account major seasonal variations that could impact the findings.