Shellfish reefs are complex, three-dimensional living structures, which provide food, shelter and protection for a range of other invertebrate and fish species.
Shellfish reefs occur in bays, estuaries and nearshore coastal waters in both tropical and temperate regions across every state within Australia. They provide habitat for other species by creating a hard substrate with high surface complexity, acting as attachment sites for sessile organisms and refuges for mobile organisms, supporting high levels of species diversity. Shellfish reefs largely occur in the intertidal and upper subtidal regions of bays, estuaries and nearshore waters with the exception of the native flat oyster (Ostrea angasi) which can form reefs at depths of up to 30m.
Although shellfish reefs are among the most threatened marine habitats on earth, little information is currently available on the ecology of shellfish reefs. Australian shellfish reefs are no different, with only a few species studied in detail (Saccostrea glomerata and Crassostrea gigas). Most Australian shellfish research focuses on describing life history, feeding, husbandry and disease in cultivated species (Crassostrea gigas, Ostrea angasi and Saccostrea glomerata) in support of shellfish aquaculture.
Shellfish reefs can be created by a single shellfish species (e.g. Saccostrea glomerata), or comprised of several reef-building species (for instance where Ostrea angasi co-occurs with Mytilus galloprovincialis or Pinna bicolor). Although shellfish reefs can vary in appearance depending on the dominant reef-forming species, they share a number of common attributes:
- They provide habitat for other species by creating a hard substrate with high surface complexity, acting as attachment sites for sessile organisms and refuges for mobile organisms, supporting high levels of species diversity;
- They accrete dead shell material such that the reef grows in size and mass over time (except where restricted by tidal exposure or when harvested) with decay occurring at varying rates;
- They provide food for other organisms, either when consumed directly or through the species assemblages they support.