The Lobster's Life Cycle
The Early Years / Molting & Growing / Mating and Pregnancy
The Early Years

The first few years of a lobster’s life are precarious. Of the 10,000 eggs that a female may release only 1/10 of 1% may survive. (That’s only 10 eggs!!) The life cycle of the American lobster begins with the planktonic phase.  During this phase the larvae are free-swimming and stay this way for 3-10 weeks.  The amount of time they stay in this stage, as well as their growth and their survival, depends on environmental conditions, such as water temperature, currents and predation.

The planktonic phase begins when eggs are hatched, and the larvae head towards the ocean surface.  At this stage each of these tiny lobsters are the size of a mosquito and in no way resemble their parents. (This is why lobstermen often refer to lobsters as “bugs”)  These reddish-green larvae that breathe through external gills and swim with their appendages feed on small planktonic organisms.  The feathery hairs on their legs are what help propel them through the water for the first month or so because their swimmerets have not yet developed.

Larvae are usually found in the top meter of the ocean’s surface bobbing up and down.  Here, in this top layer of water is where the lobster will shed its shell (molt) three times before entering the next phase of life. The first molt takes place between four days and a week, depending on the temperature of the water. At this point the stage I larva molts into a stage II lobster. The stage II lobster is a little larger and has developing swimmerets.  At the end of stage II the lobster will molt for the second time resulting in a stage III lobster.  Although by this time it is much larger, it still has the folded appearance of the stage I larva. (The bend in the middle of the larvae is not characteristic of the adult lobster).  The swimmerets of the stage III lobster are still non-functional and the animal still swims with the aid of its front appendages.  The molt to stage IV is the most critical of all the molts because this is the point in which the lobster adopts the characteristic adult lobster shape and functioning structures. An elongated form replaces the bend that was present in the previous stages and the gills are enclosed within the gill chamber.  With its claws outstretched ahead of it, the stage IV lobster swims by propelling itself with its beating swimmerets.  By the time a lobster reaches stage IV it is between 15 days and a month old.  This stage may last for several weeks as the lobster moves up and down the water column searching for a place to settle.

Interestingly, in their early stages larvae are attracted to the bright light at the surface and move towards it, but before they are about to molt they move downwards where it is darker and deeper.  Midway through the fourth stage the tendency to move towards the light is hindered by the dominant desire to move downwards towards the bottom.  It is here where the lobster will stay.  After reaching the bottom the lobster molts to the fifth stage. 

The young lobster have now passed through the planktonic phase and have entered the benthic phase.  It is this phase in which young juvenile lobsters are shelter-bound and restricted.  It is over the next few years that these few surviving lobsters must protect them selves from predators.  After finding a home these young lobsters must change their diet from a “shelter-based” food supply to a food supply outside their shelters.  During the first year or so they capture small prey that has been carried by the seawater through their shelter.  The lobsters actually propel this water through their home by beating their swimmerets.  At this young age lobsters may also be able to eat organisms twice their size like amphipods and isopods (“sand fleas”).  As they meet their energy requirements and grow they need to venture out on short trips to find food. By this time however, they have a better chance of protecting themselves from predators because they are larger and stronger.  After a number of years lobsters are usually larger then their predators and therefore can travel greater distances with not much threat of being caught for someone’s dinner!

Molting and Growing

Because the shell of a lobster is hard and inelastic it must shed its shell in order to grow. Ecdysis, commonly called shedding, occurs when a lobster extrudes itself from its old shell.  The overall process of preparing for, performing, and recovering from ecdysis is known as molting.  Unlike animals that are soft-bodied and have skin, a lobster’s shell, once hard, will not grow much more.  Lobsters show intermediate growth; that is, they grow throughout their lives and therefore spend much of that time preparing for, or undergoing ecdysis. 

Between molts a lobster’s flesh becomes densely packed within its shell, and a new shell, soft and flexible, is laid down inside the old.  Shortly before molting several things take place.  Calcium is moved from the old shell and deposited in special structures called gastroliths that are located on the stomach wall.  As blood leaves the appendages the flesh of the claws shrivels to about a quarter of their normal size to make it easier for them to be withdrawn.  Just prior to molting, a lobster absorbs lots of water, which causes the new shell to swell, eventually pushing away the old one.

During the molting process a lobster throws itself into a V-shape, lies on its side and begins to withdraw from its old shell.  The withdrawal begins when the large flexible membrane that joins the carapace and abdomen stretches and splits.  At the beginning of the molt the membranes holding the gastroliths break and the calcium is thrown into the stomach.  From there it is re-absorbed so that it may help in the immediate re-hardening of the new shell.  Escaping from its old shell may take the lobster anywhere from several minutes to a half hour, depending on environmental conditions and the size of the animal.  Once free of the old shell the lobster flips itself into its normal position.

Over the next few hours the lobster, who resembles a black rubber toy, will absorb water and will swell to reach its new size.  By gaining this sea water it may gain about 15% in size and 40-50% in weight.  The new shell has everything the old shell had, including all the same appendages, gills, mouthparts, antennae, antennules, eyestalks, and pleopods, as well as every hair, spine and bristle!  Amazingly a lobster even has the ability to regenerate lost appendages.  For example, a lobster may “throw” a claw to escape a dangerous situation, such as a fight with another lobster.  After its next molt the claw will begin to regenerate, and eventually a new claw will replace the lost one.

Molting takes place within the safety of the lobsters burrow.  Because of its new soft shell the lobster is easy prey and must remain in hiding for at least a week or two.  A newly molted lobster will begin to eat its old shell and other material high in calcium in order to strengthen its new shell.  During the months that a lobster shell takes to fully harden, tissue replaces the water that was gained prior to molting.  In effect, the lobster fully grows into its shell and the cycle of molting and growing begins again.

 Many factors control when a lobster will molt; water temperature, food supply, salinity, type of bottom, depth of water and availability of shelter are some examples.  Although lobsters molt quite frequently at first, five or six times in the first season, as they grow the length of time between molts increases.  An adult lobster will molt only once or twice a year.  In very cold waters, however a lobster may go two years without molting.  Areas with warmer water have faster growing lobster (basically lobsters that molt more frequently) then areas with cold water.  Males grow faster then females, and females may go two years between molts when they are carrying eggs.  Female tails grow considerably larger then males’ tails, but male claws grow larger then females’.  In the largest lobsters, claws can make up 45% of the total body weight. 

Mating and Pregnancy

A female lobster can mate only after it has just molted whereas a male can mate immediately before or after molting.  When a female is ready to molt she will wander around the neighborhood searching for the den of the largest, dominant male.  Outside the den she will spray out chemicals, called pheromones that indicate to the male that she is ready to mate.  These chemicals are actually released in a stream of urine that is sprayed out via the openings just below her antennae.  If the male is ready to mate he will permeate his den with this scented water by beating his swimmerets.  After this occurs, the male will come out from his den with his claws raised aggressively.  The female can either face the male and accept him or turn away.  If she places her claws on his head then he knows she is ready to mate and they will enter the den together. 

Several hours to several days later, this being different for every female, she molts. The male who is still hard-shelled must be careful not to tear her soft flesh as they mate.  The male who has flipped the female on to her back, will insert his first pair of swimmerets, which are rigid and grooved, into a receptacle called the spermatheca, located between the last two pairs of legs in the female.  The sperm that is passed through the grooved funnel of the swimmerets is released from the sperm ducts, located at the bases of the male’s fifth walking legs.  A mucus type plug will seal the spermatheca and the female will carry this sperm she has received until she lays her eggs, which may be up to a year or so after mating.

Eggs are released from the opening of the oviducts at the base of the female’s third walking legs. When she is ready to release her eggs (as many as 10,000-80,000!!) she turns on to her back and cups her tail. As she releases the stored sperm from her spermatheca to fertilize them, the eggs are passed to her tail, where a sticky substance glues them the bottom.  She carries the eggs for 9-11 months and fans them with her swimmerets, bringing them oxygen and cleaning off debris that might be sticking to them.  It may take up to two weeks for a female to release all her eggs because the eggs are released in intervals. 

When it is time for them to hatch (scientists do not know precisely how the female knows its’ time) she lifts her tail into the current and sets them out to the great unknown


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