Anoyster reef is a dense aggregation ofoysters forming a large colony. Because oyster larvae need to settle on hard substrates, new oyster reefs form on stone or hardmarine debris. Later, the oyster reef will grow byspat settling on the shells of older or nonliving oysters. These dense aggregations of oysters are also called oyster reefs, oyster beds, oyster banks, oyster bottoms, or oyster bars, with no clear distinction and with regional variation.

Oyster reefs were once common in estuaries around the world.^[1] Over the last few centuries there have been significant declines in the extent and condition of oyster reefs globally,^[2] driven by overharvesting of oysters for food provision, lime production, and coastal degradation.^[1]Boat wakes can cause oyster shells to be swept toward the shore, where they build up over time into exposed piles in which any remaining oysters will desiccate and die.^[3] These piles may also isolatelittoral areas from tides and currents, leading to further habitat degradation.^[3] Laboratory experiments suggest that in areas of faster flow and higher amounts of suspended sediment, as would be seen in a high-traffic channel, thecyprid larvae ofbarnacles may outcompete larval oysters in settling onto substrate, a prerequisite for completing their respective life cycles.^{[4]: 40–48}

In the United StatesCrassostrea virginica, theeastern oyster, was a major reef builder in the Chesapeake Bay until the late 19th century. Because ofoverfishing,environmental degradation, and disease, populations ofC. virginica underwent a drastic reduction in population size.^[5] There is an established pattern connecting human fishing practices, such asdredging, to oyster population collapse across the globe. Besides the collapse ofC. virginica reefs on the east coast of the United States, populations of the Olympia oyster,Ostrea lurida, on the western coast of the United States and theSydney rock oyster,Saccostrea glomerata, of eastern Australia have both been heavily impacted by harmful fishing practices.^[6] While most research has focused on temperate zones it is likely that significant declines have also occurred in tropical regions.^[7]

TheIUCN's Overall Risk Category assessment of the oyster reef ecosystem in southern and eastern Australia has labeled them ascritically endangered.^[8]

Natural oyster reefs are composed of living and dead oyster shells and provide important habitat for various species.^[5] For example, the complex three-dimensional interstitial spaces within oyster reefs provide refugia for prey or juvenile species, which increases prey biomass and thereby enhances trophic transfer. Oyster reefs also stabilize shorelines by promoting sediment deposition and buffering wave energy, thereby allowing other habitats such assea grass beds and marsh areas to form while simultaneously decreasing erosion of the shoreline.^{[9][10][11][12]}

The filter feeding behavior of oysters can buffer against environmental degradation caused by human-inducedeutrophication of estuary systems. Oysters feed on suspendedphytoplankton and other organic matter. Disruption of the filter feeding by oysters can lead to a decrease in the elimination of organic matter from thewater column and increase phytoplankton abundance. This in turn may lead to seasonal anoxia, which could increase mortality for other estuary animals, such as fish.^[5]

Oyster reefs can also impact thecarbon sequestration and excess nutrient uptake. Oyster reefs also stabilize shorelines by promoting sediment deposition and buffering wave energy, thereby allowing other habitats such as sea grass beds and marsh areas to form while simultaneously decreasing erosion of the shoreline.^{[9][13][14][15]} Oyster reef habitats have been recognized asgreen infrastructure for shoreline protection.^[16]

Oyster reef restoration has accelerated in recent decades.^[17] Oyster reef restoration projects often place the sanitized shells of dead oysters, concrete, or limestone pieces on a soft bottom to encourage oyster spat settlement.^[10] Restoration of intertidaleastern oyster reefs can match natural densities of oysters andmud crabs, and recover oysterstability in about 6 years.^[18] Additional benefits to restoring these habitats includes suppressing phytoplankton blooms via increasing filter feeding behavior,^[19] increase nutrient sequestration anddenitrification rates,^[20] increasenekton biomass, and potentially increase commercial fishery value.^[21] However, data on previously implemented restoration projects can be difficult to access, hindering future restoration efforts.^[22]

• Rudists – extinct group of major reef-building bivalves in the Mesozoic Era

• Animation of Reef Development from The Nature Conservatory Australia
• South Carolina Oyster Recycling and Enhancement Oyster Biology & Ecology

• Oysters
• Reefs

• Articles with short description
• Short description matches Wikidata