A question of complexity: how to rebuild lost oyster reefs.

By 01/03/2024Current Projects
HSF 22054 | Amount: $71,621 | Project Leader: M Bishop | Project Period: 0

A project undertaken at Macquarie University, and supervised by A/Prof Melanie Bishop. 

Oyster reefs are one of Australia’s most critically endangered marine ecosystems. Oyster reefs form when successive generations of oysters settle and grow on top of one another, forming three dimensional structures analogous to coral reefs. These structures provide food and habitat to a range of fish and invertebrate species, play a critical role in filtering and maintaining clean water, and provide shoreline protection. Along the southeast coast of Australia, once abundant oyster reefs have been reduced to 8% of their former abundance due to historic overharvest using destructive dredging methods, that removed not only live oysters but the dead shell base on which reefs grow.

As awareness has grown as to the extent of oyster reef loss, and the socio-ecological benefits of reinstating these important ecosystems, so too have attempts to restore them. Along sections of coastline where the aquaculture industry or remnant oyster populations provides a source of larvae, restoration has typically involved providing a hard base for oyster reef growth.

In places with large populations of fish, crab and whelk, such attempts at restoration are contingent on providing juvenile oysters with adequate protective spaces from predators. Materials with complex surface geometries can provide protection from predators and environmental stressors. However, it is unclear what specific geometries are most effective.

Porto Bay

This study will increase the success rate of oyster reef restoration projects, by developing methods for reducing predation, and enhancing reef growth. It will do so by developing knowledge of which surface geometries of substrates are most effective for oyster reef reestablishment, across a range of environmental conditions.

Firstly, using field experiments comparing colonization of 16 different geometries of substrate, it will disentangle how rugosity (the surface roughness), fractal dimension (a measure of geometric irregularity) and vertical height independently and interactively influence oyster establishment and growth influence reef formation and growth under varying conditions of predator access (manipulated through caging). It will also assess how such effects of substrate geometry vary according to larval supply.

The results of this research will be of strong interest to government and non-government organisations that are actively engaged in on-ground restoration works. The results will be used to design oyster reef restoration projects that maximise reef re-establishment, and thereby deliver significant environmental and economic benefits to Australia.