What is an oyster reef?

Oyster reefs are dense clusters of oysters that grow on hard surfaces like rocks, old shells, or even other oysters and whelks in shallow coastal waters. These reefs provide vital habitat for marine life.

Why are they endangered?

Globally, over 85% of oyster reefs have been lost due to destructive harvesting, dredging, pollution, disease, and coastal development. In Australia, the loss is estimated at more than 95%. A major driver of this decline was the widespread harvesting of oysters for their shells, which were burned to produce lime—a key ingredient in cement. While these figures mostly relate to southern temperate waters, oyster reefs are now being discovered across tropical Australia, although there is little evidence yet of how extensive they once were.

What’s the situation in Queensland?

A recent Griffith University study uncovered historic mentions in local newspapers of 23 oyster reefs across 14 locations between Townsville and Port Douglas—most of them long forgotten. Connecting with Traditional Owners may help to bridge the scientific knowledge gap. OzFish has mapped and helped ground-truth many of these sites and has discovered numerous remnant reefs—but only in remote areas. Priority reefs are being selected for restoration.

What do we know about tropical oysters?

Tropical oysters show greater species diversity, grow more quickly and reproduce more often than their southern counterparts.

Why restore reefs?

Oyster reefs provide powerful ecological benefits. They stabilise shorelines, filter and clean water, and create vital habitat for a rich community of invertebrates like crabs, worms, and prawns, which are important food sources for fish.

How much water can they filter?

A single adult oyster can filter up to 180 litres of water per day. Multiply that by thousands or even millions of oysters, and you’ve got a natural water purification system that can dramatically improve water quality.

How are they being restored?

Despite the scale of decline, oyster reef restoration is proving successful both overseas and around Australia. The process involves laying down hard surfaces like recycled oyster shell or limestone and allowing wild oyster larvae to settle—or adding hatchery-grown spat (young oysters) and protecting the site so the reef can grow.

How can you get involved?

OzFish is building a national database of the remaining tropical shellfish reefs. If you spot a reef or shellfish cluster, you can help by reporting it at: ozfish.org.au/projects/great-shellfish-hunt