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Oyster reef

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Through Environmental degradation, Eutrophication and Green infrastructure

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Degradation of oyster reefs

Oyster reefs were once common in estuaries around the world. Within the last century there have been significant declines in the extent and condition of oyster reefs globally, driven by overharvesting of oysters for food provision and lime production, and coastal degradation. 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. These piles may also isolate littoral areas from tides and currents, leading to further habitat degradation. Laboratory experiments suggest that in areas of faster flow and higher amounts of suspended sediment, as would be seen in a high-traffic channel, the cyprid larvae of barnacles may outcompete larval oysters in settling onto substrate, a prerequisite for completing their respective life cycles.

In the United States Crassostrea virginica, the eastern oyster, was a major reef builder in the Chesapeake Bay until the late 19th century. Because of overfishing, environmental degradation, and disease, populations of C. virginica underwent a drastic reduction in population size. There is an established pattern connecting human fishing practices, such as dredging, to oyster population collapse across the globe. Besides the collapse of C. 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 the Sydney rock oyster, Saccostrea glomerata, of eastern Australia have both been heavily impacted by harmful fishing practices. While most research has focused on temperate zones it is likely that significant declines have also been observed in tropical regions.

The IUCN's Overall Risk Category assessment of the oyster reef ecosystem in southern and eastern Australia has labeled them as critically endangered.

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