American Lobster

Natural History and Biology

Lobsters belong to the arthropod phylum along with crabs, spiders, insects, centipedes and other invertebrates with jointed legs like a human's elbows or knees. They belong to the class Crustacea and these animals are characterized by having a hard, external shell that protects their body. Most live in saltwater and breathe through gills, just like fish. They have many pairs of legs, and their bodies are jointed. Crustaceans use feelers for touching, feeling and smelling. Lobsters and true crabs are members of the Order Decapoda and this simply means that they have ten legs (5 pair).

Dorsal view
The American lobsters crawl more often than swim. The first pair of walking legs is modified to form the large familiar claws. A lobster does display handedness and the crusher claw is considered the dominant claw. Therefore if the crusher claw is the right claw the lobster is considered right handed. Although there are usually three main body sections, in the lobster the head and thorax are fused forming what we call the cephalothorax. The walking legs are attached to this section that is also referred to as the carapace. These walking legs and the edges of the carapace are covered with fine hairs that also help the lobster explore its environment. The single pair of long antenna is used to sense its physical surroundings. There are also two pair of smaller antennae (antennules). These are the lobster's nose. They are covered with fine hairs that are very sensitive to odors in the water. This is how the lobster locates its food. The compound eyes are on mobile stalks like flowers on a stem. The abdomen is strong and muscular, with a strong-segmented exoskeleton ending in the tail (telson).

Ventral view
The mouth is just below the rostrum, under the eyes and between the antennas. It includes the maxillipeds and mandibles. Lobsters use the maxillipeds to bring food to the opening of the mouth and the mandibles act as teeth. If you look closely you can see what looks like a comb on the inside edge of the maxillipeds. These however, are not the teeth that grind up the lobster's food. We will discuss that later. The abdomen has six pair of swimmerets; the last pair is enlarged to form the tail fan. The first (closest to the cephalothorax) is different from the four others and can be used to differentiate males from females. For males, the first swimmerets are large, hard and whitish, and are used for mating. They are called gonopods. For females, they are small and soft. The other pairs of swimmerets help lobsters move or make the water inside their shelters circulate. For females, they are also used to carry and ventilate eggs. The gills are located at the base of the walking legs just under the carapace.

Internal anatomy
Lobsters do not have a true brain but rather a mass of neuron (~100,000 compared to our 100 BILLION) located just behind the eyes and decentralized. The lobster "brain" is about the same size as that of a grasshopper's. In fact if it was possible for you to dissect out the nervous system of both an adult lobster and a grasshopper you would have a difficult time discerning the differences. The heart is located on the internal dorsal surface near the posterior end of the cephalothorax. The heart is a single chambered sac that pumps blood through vessels, sinus cavities and over the gills. The blood is pumped forward through major arteries to supply sensory organs and vital systems. No veins are present to return blood to the heart! Can you guess why? We have veins to bring deoxygenated blood from our organs and tissues toward our heart to be pumped to the lungs to pick up oxygen. Since the lobster does not have lungs and since oxygen is picked up directly from the gills veins are not necessary. The lobster's circulatory system is called an "open" system. The heartbeat is regulated by neural impulses from the "brain" (neurogenic) as compared again to ours, which is controlled by our heart muscle (myogenic). Lobster blood is a clear fluid and may turn into a whitish gel when the animal is cooked.

A lobster has two stomachs. The first is located just behind the eyes and brain (cardiac stomach) and the second is right behind the first and is called the pyloric stomach. Teeth for grinding food are located in the cardiac stomach and are referred to as the gastric mill. The intestine begins immediately after the pyloric stomach and extends the length of the body to end in anus. When you remove the lobster's tail before eating you may notice a black line - that is the intestine. There are two urinary bladders that are located on their heads where it is convenient for them to let out plumes of urine to mark their territory or attract a potential mate in the area. Imagine! Urinating our your nose!

The lobster doesn't have a liver but has a large organ called the digestive gland that serves a similar function in the lobster as our liver. This large organ removes and collects toxins, and although many people like to eat this green "stuff" it probably is not very wise. Lobsters can accumulate extremely high levels of toxins (as much as 9 million times that of the water in which they live) such as PCB's, dioxins, mercury, lead, and arsenic, which can cause health problems ranging from kidney damage and impaired mental development to cancer and even death. Lobster digestive gland, or "tomalley," which some people consider a "delicacy," are especially dangerous. The high doses of toxins concentrated in the livers can cause paralytic shellfish poisoning.

Now the pink stuff or coral you may see in your boiled lobster is a mass of unfertilized eggs - so you know you have a female. The ovaries run along the body above the intestine. Sometimes, there's a black slimy substance that is not very appealing but is what happens to eggs that cannot be extruded (mostly because the lobster was stressed due to capture). So instead of being laid they are liquefied. Just rinse the mass out of the body and it is still good to eat. In the male the testes are directly below the heart and appear as two white lines.

Smell
Lobsters have the most acute sense of smell in the ocean. Better than sharks! The small hairs that cover the small antennae act as the nose. These hairs are extremely sensitive to amino acids, the basic building blocks of proteins, and thereby indicative of potential prey items. As the lobsters is crawling around hunting for its next meal the animal "flicks" the antennules. This flicking is analogous to us sniffing the air to follow the smell of freshly baked cookies. Because the lobster has two pair of the antennules they can determine the direction of the smell by comparing the difference in concentration between the antennules.

Touch
The long antennae can be compared to the whiskers of a cat in that the lobster uses them for the sense of touch and to determine if a space is large enough for it to pass through. These are the structures the lobster will use to find hiding places and the doors of a lobster trap. When lobsters fight for territory these are the first structures attacked. Can you guess why? Well, if the lobster's antennas are small then it can only sense small opening and therefore will have great difficulty in finding a hiding place. NOTE: Lobsters to not usually fight to the death. There are also tiny hairs covering the entire body and walking legs that are sensitive to touch. The antennae and hairs help orient the lobster by discerning water movements.

Taste
The legs and mouthparts posses the taste organs. You might say the lobster tastes with its feet! Yuk! The taste organs are also hairs but a different shape than those hairs used for touch. So if the lobster likes what it is walking over it will pass the material to its mouth.

Hearing
Although lobsters do not possess ears they do produce sounds and capable of detecting low frequency sounds. (Lobsters do not have vocal cords so how they make these sounds is still a mystery.) It is assumed they feel the vibrations of the sound waves. Sounds are not made during social interactions but can be felt by a diver plucking a lobster from its den. The purpose is not known but may be some sort of defense mechanism.

Vision
Each eye is made up if approximately 12,000 individual units. Although the eyes sound rather complex it is believed that lobster eyesight is not very good - being able though to easily detect movement. These eyes also do not have lenses so the eyes work by reflection rather than by refraction that our own eyes and those of most other animals use.

Lifestyle
When a lobster is first hatched it does not look anything like the adult. Another reason why lobstermen may call them bugs. And this larval lobster has already molted 5 times! Feathery hairs on its legs help it swim (as it is now a member of the plankton community) for about a month after hatching. This is a very dangerous period in the lobster's life. It is prime food for many predators - birds and larger fish - and why only about 1% of all lobsters that hatch survive to market size. It will molt another three times before it looks like something you would recognize as a lobster. By that time it is called a "fourth-stage" lobster and is between 15 days and a month old. This little lobster is a very good swimmer and is actively looking for a place to settle on the bottom. This stage has been called the "superman" stage because the little lobster swims with its large claws outstretched and looks to be flying through the water column. Lobsters seem to be fairly particular about where they settle in. They seem to prefer rocky or cobble bottoms that have lots of hiding places and lot of nooks and crannies through which food can drift.

After the lobster has found suitable substrate it settles on the bottom and molts to the fifth stage. This little lobster is only about 1 ½ " long and still has many enemies. It will spend the next year struggling to survive in its "hide-out". Cod, sculpin, eel, skates, other lobsters, etc will attack if it leaves its shelter. Survival depends upon bits of food carried in the water that the lobster manages to pump through its "home." The tiny lobster spends the next 3 or 4 years hiding among the seaweeds and rocks surviving on whatever food items drift down. For I hope what seems an obvious reason, lobsters from childhood through adulthood are nocturnal.

Adolescent lobsters (a few years old through market size) prefer areas with larger boulders. Adult lobsters don't seem to care - they'll go anywhere and sometimes migrate long distances. They (adults) also have fewer predators.

Molting
The lobster molts, or shed is shell, up to 25 times in its first five years. As an adult it will molt about once a year. The number of times an adult lobster will molt is largely dependent upon food availability and water temperature. Molting is a very dangerous process. When the lobster is ready to molt the flesh inside the claws shrivels to about a quarter normal size, as water and blood leave the appendages. The flesh begins to reabsorb some of the calcium that will help harden the new shell. Some of the calcium is stored in a structure called the gastrolith (stomach stone) deposited on the outside of the cardiac stomach.

The old shell cracks along the joint that separates the carapace from the abdomen 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 and the lobster must throw the claw and abandon both the shell and flesh. The primary reason molting is so dangerous and difficult for the lobster is that while molting the lobster cannot breathe. Rather than suffocate the lobster abandons a claw. The is called autonomy and will be discussed later. The remaining old shell is a perfect double of the lobster, down to the claws, legs, mouthparts and even the coverings of the eyes. Most lobsters will eat the old shell to help harden the new the new one more quickly. While the new shell is still soft, the lobster absorbs seawater to gain about 15% in size (to provide for growth once the shell hardens) and 40 - 50% in weight. A just molted lobster feels "rubbery". When lifted from the support of the water its large claws will hang loosely, in fact, the claws are vulnerable to falling off from their weight. (So when purchasing a lobster for dinner check to see that the shell is good and hard otherwise you may be paying for a lot of water!)

Autonomy
This is really cool! Autonomy is reflex amputation. A lobster can discard a limb to allow escape (from a predator or during the molting process) and prevent serious injury or death. Like most invertebrates lobsters have the ability to regenerate some of their body parts – claws, walking legs and antennae. Imagine being able to drop a limb and continue on their way as though nothing had happened! This also indicates a probable lack of pain (at least ion those regions), a primitive nervous system and unlikely that lobsters feel any real pain when put into a pot of boiling water.

Courtship and Mating
For more than twenty years, Dr. Jelle Atema of the Marine Biological Laboratory has been studying lobster-mating behavior. He claims lobsters make tender lovers. A female lobster can mate only just after she sheds her shell. Lobster society has evolved a complex, touching courtship ritual that protects the female when she is most vulnerable. When she is ready to molt, the female lobster approaches a male's den and wafts a sex "perfume" called a pheromone in his direction. Unlike a female moth, whose sex pheromone may attract dozens of random suitors, the female lobster does the choosing. She usually seeks out the largest male in the neighborhood and stands outside his den, releasing her scent in a stream of urine from openings just below her antennae. He responds by fanning the water with his swimmerets, permeating his apartment with her perfume. He emerges from his den with his claws raised aggressively. She responds with a brief boxing match or by turning away. Either attitude seems to work to curb the male's aggression. The female raises her claws and places them on his head to let him know she is ready to mate. They enter the den, and some time after, from a few hours to several days later, the female molts. At this point the male could mate with her or eat her, but he invariably does the noble thing. He gently turns her limp body over onto her back with his walking legs and his mouth parts, being careful not to tear her soft flesh. They mate "with a poignant gentleness that is almost human, " observes Dr. Atema. The male, who remains hard-shelled, inserts his first pair of swimmerets, which are rigid and grooved, and passes his sperm into a receptacle in the female's body. She stays in the safety of his den for about a week until her new shell hardens. By then the attraction has passed, and the couple part with hardly a backward glance.

A lobster's pregnancy is long: from mating to hatching takes perhaps twenty months. After mating, the female stores the sperm for many months. When she is ready to lay her eggs, she turns onto her back and cups her tail. As many as 10,000 to 20,000 eggs are pushed out of her ovaries. They are fertilized as they pass through the sperm receptacle, marked by a small triangular shield at the base of her walking legs. A sticky substance glues the eggs to the bottom of the female's tail. She will carry the eggs for 9 to 11 months, fanning them with her swimmerets to bring them oxygen and to clean off any debris that might stick to the developing eggs. Finally, when it's time for the eggs to hatch, the female lifts her tail into the current and sets them adrift in the sea. It may take up to two weeks for all of the eggs to be released.

How old IS a lobster?
This is a very common question. How old is a lobster we can purchase in the market? When we are told that the lobster is 6 or 7 years old before it reaches market size that is our best guess. Remember that growth or the number of times a lobster molts is dependent upon food availability and temperature. So if the conditions are not ideal the lobster may in fact be 7 or 8 years old. Another thing that contributes to overall size is how often the lobster had to regenerate body parts. An interesting fact is that when an animal is regenerating ALL other growth stops. What this means is that if the lobster drops a claw all of the growth energy produced is put towards growing the new claw. Once the new claw (or leg, or antenna) is the appropriate size for the rest of the animal then entire body growth continues. So, if our lobster has had a particularly traumatic adolescence it may be 10 or more years old before it reaches market size. The next obvious question might be – How big can a lobster get? If left unmolested a lobster continues to grow throughout its life. The record so far is a lobster caught in Massachusetts. This lobster weighed 44 pounds, 6 ounces and the carapace was between 3 and 4 feet! It is guestimated that this animal was approximately 100 years old!

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