THE STEINHART AQUARIUM - Gulf of Guinea Science ...

72 A Docent Field Guide to the Species of the Steinhart Aquarium
Appearance: Carapace to 23 cm across in
males, to 16.5 cm in females.
Diet: Adults are rather non-discriminating
nocturnal carnivores. Diminutive crustaceans
are favored prey items. Small bivalves are also
consumed; shells are crushed or opened by
chipping away the margins with their powerful
claws. Also consume worms and fishes as well
as fresh carrion.
Reproduction and Development: Mating
occurs from April to September in British
Columbia and perhaps earlier in California.
Females able to retain viable sperm for up
to several months; gravid mostly during
November to February and spawn between
September and December. Clutch from 700
thousand to 2.5 million eggs. Hatching begins
during December, peaking during March.
Molting of the adults follows reproduction.
Mortality/Longevity: Larval stages are eaten
in enormous numbers by herring, pilchard and
salmon. Crabs live to eight years or possibly
longer.
Remarks: Largest edible crab on the North
American west coast. Accounts for 99%
of all crab species taken commercially in
California.
Red Rock Crab
Cancer productus (Cancridae)
Distribution: Alaska to Baja California.
Habitat: Rocky areas of bays and estuaries;
found on gravel, rock, and sand; often buries
itself in sandy substrate.
Appearance: Carapace usually a reddish color
in adults, juveniles highly variable, often with
stripes. Large claws with black tips. A large
crab, up to 18 cm across the carapace.
Diet: Voracious hunter of live and dead organic
matter. Most active at night. Uses powerful claws
to open clams, mussels, snails, barnacles, as well
as to catch smaller crabs and hold dead fish.
Reproduction and Development: Mating
occurs most often in summer after female
has molted. Males will often guard a molting
female until her exoskeleton hardens. Female
may carry up to ½ million eggs on her pleopods
(swimming appendages).
Mortality/Longevity: Preyed upon by fish and
seabirds, such as gulls.
Remarks: Large and good eating, but not
plentiful enough for commercial catch.
Nasty fighters; known to pinch painfully
through neoprene gloves of curious SCUBA
divers.
Green Shore Crab
Hemigrapsus oregonensis (Grapsidae)
Distribution: Alaska to Baja California. The
common shore crab of San Francisco Bay.
Habitat: Open mud flats, algal mats, eelgrass
beds in bays, estuaries, and on open beaches.
Appearance: Many color variations from
grayish green to white, often mottled; carapace
up to 5 cm.
Diet: Feeds mainly on diatoms and green algae,
but will scavenge and take meat if available.
Feeds primarily at night.
Reproduction and Development: Females
brood up to 4,500 eggs per mating. Larvae
spend about 5 weeks in the plankton before
metamorphosis and settling. Females may
mate twice a year.
Mortality/Longevity: Preyed upon by various
shorebirds. These crabs are good diggers, and
can bury themselves rapidly in sand to escape
predators.
Conservation Status: While our native green
shore crab is still plentiful, their population may
be seriously compromised by the aggressive
European green crab (Carcinus maenas), which
feeds on the smaller H. oregonensis and may
displace it from its favored habitats.
Remarks: This small crab tolerates varying
salinities and temperatures well, and so is
common in estuaries where salt and fresh
waters mix.
Purple Shore Crab
Hemigrapsus nudus (Grapsidae)
Distribution: Alaska to Baja California.
Habitat: Rocky shore, upper to low intertidal under
stones and among seaweeds. Less common
along clay banks in sloughs and estuaries.
Appearance: Carapace to 5.5 cm wide in males,
3.5 cm in females; smooth and convex anteriorly,
flat posteriorly. Usually colored purple,
occasionally yellow-green or reddish brown.
Diet: Diatoms and other algae. Also scavenge
animal material.
Reproduction and Development: In Central
California breeding occurs from November