The hollow oyster, Crassostrea gigas, is the leading French aquaculture species, but it is also a key bivalve from an ecological point of view in the estuarine and coastal environments it inhabits. A so-called “ecosystem engineer” species, oysters form biogenic constructions, even real reefs that rise above the sediment and constitute precious habitats for other species. Their mere presence therefore enriches marine biodiversity locally. Sometimes more than 50 different species benefit from these biogenic habitats. Other ecosystem services provided by oysters include stabilising sediments and combating coastal erosion, but also maintaining good water quality with the control of turbidity and phytoplankton blooms (some of which are toxic to the environment or to humans).