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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!
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.
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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