The lobster molts, or sheds its shell, up to 25 times in its first 5 years of life. As an adult, it molts about once a year, until it becomes quite large, at which point it may go several years between molts. Molting is hard work. In advance of molting, the flesh inside the claws shrivels to about a quarter of normal size, as water and blood leave the appendages. The lobster's shell weakens, as the flesh reabsorbs some of the calcium that will help harden the new shell. Some of that calcium is stored in a structure called a gastrolith (stomach stone) deposited on the outside of the forgut. The old shell cracks along the joint that separates the carapace (the back shell) and the tail and along a line down the middle of its back. The lobster lies on its side and flexes its body several times to pull itself from the cracked shell. Even though the claw muscles have shrunk, they sometimes get stuck in the narrow knuckle of the claw during molting, and the lobster must throw the claw and abandon both the shell and flesh.
The remaining old shell is a perfect double of the lobster, down to the claws, legs, mouth parts, and even the covering of the eyeballs. The lobster eats its old shell to help harden the new one more quickly. While the new shell is still soft, the lobster absorbs sea water to gain about 15% in size and 40-50% in weight. A just-molted lobster feels like a rubber toy. If it is lifted from the support of the water, its heavy front claws may drop right off. It stays in hiding for a week or two until the new shell is fortified against predators.
Much of the weight of a "shedder," or newly-molted lobster, is water, as disappointed diners who crack open a soft-shell lobster quickly learn. That allows the new shell to accommodate the growing lobster for a year or more. Most of us can remember our parents using a similar concept when they bought us clothes several sizes too big to give us some "growing room."
Many factors control when a lobster will molt: water temperature, food supply, salinity (the amount of salt in the seawater varies from place to place and from season to season), availability of shelter, the type of bottom, and the depth of water. Lobsters living in warm water grow faster than those in cold water. Experiments have shown that lobsters raised in hatcheries with water at 70 degrees Farenheit can grow to one pound in less than two years, while in the frigid waters of the north Atlantic, it takes a lobster 5 to 7 years to reach this market size, known as a "chicken lobster." Males grow faster than females, and females may go two years between molts when they are breeding. Female tails (abdomen) grow relatively larger than males' tails, but male claws grow larger than females'. In the largest lobsters, claws make up as much as 45% of the total body weight.
p.3 - Handout 4-A
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