Eighteen kilometres southwest of Rochefort is Brouage, a seventeenth-century military base. The way into the town is through the Porte Royale in the north wall of the original fortifications. Locked inside, Brouage seems abandoned and somnolent; even the sea has retreated, and all that’s left of the harbour is a series of pools (claires), where oysters are reared.

Half a dozen kilometres south of Brouages is the oyster village of Marennes. It is the centre of production in a region that supplies over sixty percent of France’s requirements. The village’s speciality is fattening creuses oysters, a species bred in France since the 1970s. It’s a lucrative but precarious business, vulnerable to storm damage, temperature changes, salinity in the water, the ravages of starfish and umpteen other natural disasters.

Oysters begin life as minuscule larvae, which are “born” about three times a year. When a birth happens, the oystermen are alerted by a special radio service, and they all rush out to place their “collectors” – usually arrangements of roofing tiles – for the larvae to cling to. They mature there for eight or nine months, and are then scraped off and moved to parcs in the tidal waters of the sea. Finally, they’re taken to claires – shallow rectangular pools where they are kept permanently covered by water that’s less salty than sea water. Here they fatten up and acquire the greenish colour the market expects. With “improved” modern oysters, the whole cycle, which used to take five years, now takes about two.