The Oyster's World is Changing

Like most French households, oysters form part of our holiday menu. This Christmas I picked up an order of 2 dozen #2 and they sat quite happily unopened in our cellar temperature fridge for several days in an uncovered plastic box. They cost €12 and had been harvested the day before market day. The producer comes up from the coast every Saturday and does steady business all morning.

 3 dozen #2 oysters from the supermarket, Christmas 2008.

Oysters are great from a consumer point of view -- they are sustainable, being farmed in a way that doesn't plunder other marine resources, and exceptionally, they are instrumental in restoring healthy intertidal habitats, even when the oyster species is not native (most commercial oyster production worldwide uses Pacific oysters).

Grilled oysters for breakfast, Christmas 2008.

I'm glad I'm not an oyster farmer though. At the moment there is a sort of triple (or even quadruple) whammy threatening oysters.

Unfortunately, oysters have been hit by an viral epidemic with a very high mortality rate. It's known as oyster herpes and can wipe out colonies in just a few days. The virus first appeared in France in 2008, and has reduced production here by 26%.

 Au naturel, Christmas 2010.

Most worrying of all, the virus only takes hold when water temperatures reach 16°C. With climate change causing globally warmer and warmer weather, the virus is set to become worse and worse. Sea surface temperatures are warming even faster than land temperatures too.

 Oysters at the market in Preuilly, Christmas eve 2011. 

The price has gone up 60¢ a dozen in 3 years.

The water temperature is not the only change in the sea being driven by climate change. The sea is absorbing carbon dioxide CO2, resulting in acidification. The sea isn't turning to vinegar, but its pH has gone down sufficiently for some effects on oysters to have been observed. It's a twofold problem. The first, and simplest to understand, is that more acidic seas cause shell, made from calcium carbonate, to dissolve.

The second effect is that as well as having their shells slowly dissolved, shellfish are having to work much harder to create shell in the first place. In the case of oysters, when they are new born, they sometimes cannot make shell at a rate quick enough to gain on the rate it is being dissolved. This leaves them even more vulnerable to predation than they would otherwise be.

 Farmed oyster beds on Ile de Ré, an island just off the Atlantic coast of France and a couple of hours west of us.

The way it works is this: 30% of atmospheric CO2 dissolves in the oceans, where it combines with water H2O to form carbonic acid. The H in pH is postive hydrogen ions. Acids release hydrogen ions into their surrounds and they bond with other molecules. One of the molecules they naturally bond with in the sea is carbonate CO3¯². This means the carbonate is not available to bond with calcium to form calcium carbonate, the key ingredient in oyster shells.

For the oyster farmers it's a looming disaster, and the oyster loving French consumer had better start preparing for something to be missing from the table at Christmas time. It's very frustrating when you consider oysters have so many positive benefits to the environment and nutritionally.

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Au jardin hier: Yesterday was the first really cold day this winter. According to the weather bureau our minimum was -7°C and I doubt if it went above 0° all day -- certainly the puddles in our driveway stayed frozen all day. I went down to the orchard to finish clearing up the fallen branches and to saw off the splintered breaks on the trees. Initially my fingers ached with the cold and as I struggled to warm them I nearly decided to come home. Luckily I finally managed to get my fingers functioning and I've completed the task.

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A la cuisine hier: Chickpea pancakes with salad. Spicy Red Lentil, Tomato and Spinach Soup -- homely and surprisingly satisfying.