Download Blue Crab - The Institute for Marine Mammal Studies

Commercial Importance
Unlike vertebrates whose skeletons grow with
them, most invertebrates must molt or “shed”
their outer layer (exoskeleton) in order to grow
larger; blue crabs are no exception to this rule.
This molting is called “ecdysis.” Ecdysis happens
in three stages: precdysis, ecdysis, and
postecdysis. Precdysis begins with a release of
hormones under their outer, hard shell. This shell
is attached to the crab with connective tissues that
separate and allow a new shell to grow underneath. Ecdysis begins when the crab generally
stops eating. The crab will then “take in” water
and crack the old shell at a specific weak point.
For the blue crab, this weak area is along the back
of the shell. The crab is now able to “back out” of
the old
shell.
The
crab
then
rapidly
suctions in
water to
swell its body to a size about 33 percent larger
than the old shell. The old shell remains empty,
but completely intact. After molting, these crabs
are referred to as “soft shell crabs.” Postecdysis is
defined when the shell begins to harden. Often the
crab will consume its molted shell in order to
obtain extra calcium.
The blue crab is one of the five most
commercially harvested species in the Gulf of
Mexico. Blue crabs were commercially harvested
as long ago as 1880. Records indicate there were
only two Gulf Coast states to take part in this
harvesting: Louisiana and Texas. In 1880 alone,
an approximate 324,000 pounds of blue crabs
were harvested valued at approximately $8,000.
By 1950, all five Gulf States had begun to
commercially harvest blue crabs; the states
landed approximately 18,816,000 pounds.
Between 2007 and 2009, an average of 55 million
pounds of blue crabs were harvested by the Gulf
states. These
55 million
pounds were
sold for an
average of 43
million
dollars.
During these
years, the blue
mediagalley.usatoday.com
crab was
ranked number four in the top five commercial
species by poundage and number five by monetary value. Many commercial blue crabbers today
use crab traps (or crab pots) to facilitate their
catch.
pbs.org
Ecdysis (Molting)
This brochure is funded with qualified
outer continental shelf oil and gas
revenues by the Coastal Impact
Assistance Program, United States Fish
and Wildlife Service, U.S. Department of
the Interior through a grant award to the
Mississippi Department of Marine
Resources.
Blue Crab Distribution
Blue crabs are natively found along the Atlantic
coast of the western hemisphere. They are found
from Canada, throughout the Gulf of Mexico and
around the curve of Brazil in South America. The
blue crab range is highlighted on the map below.
Blue Crab
Callinectes sapidus
Remember
The Institute for Marine Mammal Studies (IMMS) is
a non-profit organization established in 1984 for the
purposes of public education, conservation, and
research of marine mammals and sea turtles in the
wild and under human care. Located in Gulfport, MS,
IMMS has been an active participant of the National
Stranding Network since its inception. IMMS is a
premiere organization in the Mississippi-LouisianaAlabama sub-region of the Gulf Coast with the
capability and expertise to care for sick and injured
marine mammals and sea turtles Additionally, IMMS
promotes public awareness of marine conservation
issues through its involvement in the community.
animals.nationalgeographic.com
Prepared by Melissa Welsh, 2012
While blue crabs are predators, they are also
prey for a variety of animals, such as:

Sea bass, flounders, sharks, and catfishes

River otters and raccoons

Alligators and sea turtles
Institute for Marine Mammal Studies
P.O. Box 207 Gulfport, MS 39502
Phone:228.896.9182 Fax: 228.896.9183
Email: [email protected]
Website: www.IMMS.org
The Institute for Marine Mammal Studies
Reproduction
Phylum: Arthropoda
Sub-phylum: Crustacea
bluecrab.info
Class: Malacostraca
Order: Decapoda
Family: Portunidae
Genus: Callinectes
Species: sapidus
aqua.org
General Information
Blue crabs also have the ability to regenerate legs.
If a predator has a hold of one leg or claw, the crab
is able to selectively release the appendage and
swim away. This leg will regrow throughout several molts.
“Sally”
“Jimmy”
In general, it is easy to distinguish between male and
female crabs by viewing
their “apron” or underside.
Male crabs possess a shape
resembling the Washington
Monument or an inverted
“T.” Immature females have
a triangular shape on their
aprons, while the mature
females’ aprons are more
circular in shape. Male crabs
are often referred to as
bluecrab.info
“Jimmy” and female crabs are
known as “Sally” or “Sook” depending on her maturity. A sook is a fully mature female crab.
“Sook”
tpwd.state.tx.us
Atlantic blue crabs, or simply “blue crabs,” are given
their name not from the color of their shell, but rather
the blue colored tips of the male’s claws. The blue
crab’s scientific name (Callinectes sapidus) is derived
from the Greek and Latin languages, respectively.
This name literally translates to “beautiful, savory
swimmer.” These crabs are benthic (bottom) dwelling animals. Blue crabs are typically carnivorous
(meat/flesh-eating). Their
preferred diet includes small
fish, bivalves, and even other
crustaceans. It is not uncommon, however, for a blue
crab to eat plants or detritus
(dead and decaying plant and
animal matter). Throughout
their lives, blue crabs travel and
live within a wide range of
salinities (salt concentration). Generally remaining in
a low salinity waters, female blue crabs often migrate
to higher salinity estuaries and bays to hatch their
eggs. A blue crab’s average life span in the wild is
three to four years. Blue crabs have 10 legs: two
claws (chilipeds), six walking legs, and two swimming
legs. When grouped together, all of these legs are
referred to as “pereopods.”
References:
Coulombe, D. A. (1991). The Seaside Naturalist: A Guide to Study
at the Seashore. (pp. 128, 139-140). New York: Fireside.
Guillory, V.; Perry, H.; Steele, P.; & Wagner, T.; Keithly, W.; Pelligrin, B.; Petterson, J; Floyd, T.; Buckson, B.; Hartman, L;
Holder, E.; & Moss, C. (2001). The Blue Crab Fishery of the
Gulf of Mexico, United States: A Regional Management Plan.
Ocean Springs, MS: Gulf States Marine Fisheries Commission.
Upon hatching, the young crabs are in a larval form.
The crab in this larval stage is known as a “zoea.” At
this point, the zoeae look nothing like
a crab. Many different species of
crabs’ zoeae resemble one another.
While in this phase, the zoeae are
considered “meroplanktonic” which
refers to an organism that spends a
portion of its life as plankton
(microscopic organisms floating in
ncsu.edu
the ocean). A blue crab zoea may
molt five to seven times before entering their second
stage of life. This final molting occurs anywhere from
30 to 50 days after hatching.
The second stage of a blue crab’s life if referred to
as the megalopal stage. The young crab has come a
long way from where it started as a zoea and begins
to resemble a crab. The
megalopa exhibits signs of
10 appendages
(pereopods). On average,
the megalopal stage is completed no longer than 20
days after entering this stage.
dnr.state.md.us
Kingdom: Animalia
Life Stages
bcsp.org
Anatomy
Scientific Classification
When a female blue crab reaches maturity, she
releases pheromones (chemical-like hormones)
into the water. The males are attracted to these
pheromones and approach the female. Once the
male arrives, he embraces the female and holds
her under him to protect her. He holds her using
his first pair of walking legs. While she is offered
protection, the female molts her exoskeleton for
the last time; this molt is known as a maternal or
terminal molt. It is only following this molt that
the sook is able to mate. The male possesses two
gonopods (“reproductive foot” or penises) which
transfer packets of sperm (spermatophore) to the
storage receptacles of the female (spermathecae).
These spermatophores are stored until the female
is ready to spawn. This may happen anywhere
from two to nine months after mating. While she
may only mate once in her life, a sook is capable of
spawning several times. After mating, she begins
to form an egg sac on her abdomen. Because this
sac resembles a
sponge, a pregnant
sook is affectionately
referred to as a
“sponge crab” or a
“berried crab.” The
average female proOcean Expo Summer Camp 2011,
duces approximately
IMMS
two million eggs in
each sponge. Incubation time for these eggs varies in relationship to
the environment. The average gestation is between one and two weeks. After this time, the
young hatch and begin life on their own.
.
Following the megalopal
stage, the crab molts once
more and is classified as a
juvenile. The crab continues to
molt until it becomes an adult.
Hill, J.; Fowler, D. L.; Van Den Avyle, M. J. (1989). Species Profiles:
Life Histories and Environmental Requirements of Coastal Fishes
and Invertebrates (Mid-Atlantic)—Blue Crab. U.S. Fish and Wildlife Service. Biological Report 82 (11.100). U.S. Army Corp of
Engineers, TR EL-82-4.
National Ocean Service, NOAA. 2011. The Gulf of Mexico at a
Glance: A Second Glance. Washington, DC: U.S. Department of
Commerce.
www.animals.nationalgeographic.com/animals/invertebrates/
blue-crab/
www.bluecrab.info