Tuesday, October 11, 2005
Do oysters get bored? Of course they do. Lying around on the sea floor all day, you'd be bound to. So what bores them? Well, polychaetes, sting winkles, starfish, sponges and bivalves amongst others. All of these are oyster predators.
Oysters are sedentary, they are filter feeders. They don't bury themselves in the sediment. They need to have a stream of water passing over them from which they can extract algae to feed themselves. Basically, they are sitting targets cemented to the sea floor or an oyster farmer's nets. This is why they need such tough shells, to protect themselves.
There are basically two methods of predation. The first is to force the oyster open, the second is to drill a hole in it. Humans and starfish use the first method. Some species of starfish are actually able to pull an oyster open far enough to insert their stomach inside. Once the stomach is in place, digestion can begin.
The other method of predation, boring, is used by some gastropods, bivalves and sponges. This article records how British oysters were killed off in the 1920s when over-exploitation led to the introduction, by oyster farmers, of new species from America. These new species such as the Blue-Point Oyster didn't like their new environment, but other invertebrates that predated on them and sneaked over in the same boxes, did. These included the American Oyster Drill.
The American Oyster Drill, the Sting Winkle and the Common Whelk, are all types of marine snail which can drill a hole through an oyster's shell. They do this by softening the shell with a chemical and then rasping away with their tongues. Once the shell has been pierced, the snails gives the oyster a poisionous injection, the shell opens, and the snail tucks in.
For a Sting Winkle or a Common Whelk, this process of boring a hole can take a few days, but the American Oyster Drill is more efficient (doesn't that sound familar?) and can drill twenty young oysters a day.