THE STEINHART AQUARIUM - Gulf of Guinea Science ...

to April. Fertile females ready to molt emit
a pheromone, which attracts males. Mating
occurs after the female molts, while she is still
soft-shelled. Size of brood correlates with the
size of the female, from 441 eggs in a female
with a 1.2 cm carapace width, to more than
36,400 in a female 3.4 cm wide. One brood
per year is typical, two rarely. Hatched larvae
enter the plankton and metamorphose
through several stages before the first juvenile
crab instar.
Mortality/Longevity: Preyed upon by shorebirds
and fishes.
Striped Shore Crab aka Lined Shore Crab
Pachygrapsus crassipes (Graspidae)
Distribution: Oregon to Baja California, also
the Gulf of California; introduced to Japan and
Korean coast in the late 1800s.
Habitat: Intertidal zone in crevices, tide pools,
mussel beds; or along muddy shores of bays
and estuaries. Semi-terrestrial, living on land
at least half the time, but returning regularly
to water to moisten gills.
Appearance: Square dark body with green
cross stripes.
Diet: Feeds on films of algae and diatoms,
scraped off with claws. Also scavenges and
takes live limpets, snails, crabs, and insects.
Most active at night.
Reproduction and Development: Reach full
size in about 3 years, molting some 20 times
before maturity. Female broods about 50,000
eggs under her abdomen during each breeding
cycle.
Mortality/Longevity: Eaten by sea gulls, rats,
raccoons, and humans.
Remarks: These crabs can spend up to 3 days
out of water, depending on the water stored
in gill chambers.
Their eclectic and voracious feeding habits
make them the clean-up crew of the high
intertidal.
Masking Crab aka Decorator Crab
Loxorhynchus crispatus (Majidae)
Distribution:: Northern California south to
Baja California.
Habitat: Common on pilings, kelp beds, and
subtidal rocks to 183 m depth.
Appearance: A large crab with carapace to 9
California Academy of Sciences
73
cm in males, 7 cm in females. Often heavily
decorated, and during the day, seldom noticed
until it moves.
Diet: Algae, sponges, small crustaceans,
bryozoans.
Mortality/Longevity: An important food
source for several fishes, including croakers,
some rockfishes, and cabezon.
Remarks: Crabs in this family are known as
decorator crabs for their habit of attaching
marine algae or invertebrates to their carapace,
which has tiny hooks (setae) that hold their
“riders” securely. Different species tend to
choose different organisms as decorations.
Decorator crabs take good care of their living
symbionts. When the crabs molt, especially
when they are small and still vulnerable to
predation, they remove the “decorations” from
their old shell and apply them to the new!
The size of decorator crabs varies significantly.
One study suggests this differential reduces
competition in the wild for crevice refuges in
rocky habitats.
Decorator crab species also seem to partition
food resources, with some specializing on
species of kelp and others being more general
feeders on both plants and a variety of
animals.
They are often very destructive in our displays.
They pick and tear at anything they can. That’s
why you don’t see very many in the exhibits.
Graceful Decorator Crab
Oregonia gracilis (Majidae)
Distribution: Bering Sea to Monterey,
California; Japan.
Habitat: Intertidal to about 425 m. Often on
wharf piles or in eelgrass beds. In intertidal
areas, remains below water surface.
Appearance: Heart-shaped carapace with
long rostrum. The only decorator (or masking)
crab with a long, hooked spine behind the
eye. Long, thin, spider-like legs and pincers.
Like many of its family, is a camouflage
artist, usually liberally decorated with
algae, sponges, bryozoans and/or hydroids.
Carapace up to 5 cm.
Diet: Brown algae; also, known to eat carrion.
Reproduction and Development: Usually
spawn between May and August during spring
and summer plankton blooms.