THE STEINHART AQUARIUM - Gulf of Guinea Science ...

90 A Docent Field Guide to the Species of the Steinhart Aquarium
90 m deep. Juveniles often shelter among the
rigid outer spines of adults.
Appearance: Large red, red-brown or purple
test to 10 cm or more diameter; primary spines
5 cm or more in length.
Diet: Herbivorous upon red and brown algae;
preference is for the giant brown kelp Macrocystis.
Reproduction and Development: Breed in
the spring. Free-swimming larval period lasts
62–131 days.
Mortality/Longevity: A favored treat of sea otters.
Red sea urchins can live at least 20 years.
Conservation status: Gonad trade may be affecting
some populations.
Remarks: Raw gonads (uni) are considered
gastronomic delicacies by some people.
Removal of sea urchins promotes growth of
kelp and thus improves habitat for many other
species, including rockfish juveniles.
Purple Sea Urchin
Strongylocentrotus purpuratus
(Strongylocentrotidae)
Distribution: Vancouver Island, Canada south
to Isla Cedros, Baja California.
Habitat: Rounded burrows in rock that have
been scoured out by the present or previous
urchin using its teeth (Aristotle’s lantern) and
spines, a strategy that protects from predators
and surge.
Appearance: Test commonly 5 cm in diameter,
rarely to 10 cm. Test and spines green
to purple.
Diet: Brown and red algae. These urchins prefer
the giant brown kelp Macrocystis.
Reproduction and Development: Sexually
mature during their second year. Sexes are
separate, although hermaphrodites occur.
Most spawning occurs from January to March.
Pluteus larvae hatch, drift and settle. Growth
after metamorphosis is slow.
Mortality/Longevity: Preyed upon by sea stars
such as the sunflower star and cancer crab
species as well as fish such as the California
sheephead and shorebirds. Can live to more
than 30 years.
Remarks: Purple pigments from this urchin
lodge in the bones and teeth of sea otters,
turning the otter’s skeleton and teeth purple.
Eccentric Sand Dollar aka Western Sand
Dollar
Dendraster excentricus (Dendrasteridae)
Distribution: Southeastern Alaska to Baja
California.
Habitat: Subtidal to low intertidal zone on
sandy or sandy/muddy substrates, subtidal
to 40 m (rarely to 90 m).
Appearance: Both scientific and common
names come from the fact that the star design
is off center and somewhat lopsided, a pattern
most notable on an exposed test. The body
of the living sand dollar is covered with tiny,
closely packed purple spines. May grow to 7.5
cm in diameter.
Diet: Feeds on detritus, diatoms, and plankton
such as crab larvae and amphipods, captured
by mucous-covered spines and pincers
(pedicellariae). Particles and mucus are then
moved along groves to the mouth in the center
of the lower surface by cilia that cover the
spines. Specialized tube feet also aid in feeding
and gas exchange.
Reproduction and Development: Sexes
separate; females may produce over 350,000
eggs per year; spawning spring to summer.
Planktonic larvae that travel considerable
distances with currents settle within or near
an existing sand dollar bed, usually not near
the parent group.
Mortality/Longevity: The pink sea star
(Pisaster brevispinus), starry flounders, and
California sheephead feed on this species. Sand
dollars often bury themselves in the sand to
escape predators. Can live 6–10 years.
Remarks: This species and other sand dollars
may live in concentrated fields with up to 625
animals per m 2 . .
In calm water, eccentric sand dollars burrow
into the sand at an angle to catch nutrients. In
rougher water, they lie flat at the surface of the
sand or partly buried.
Tests of individuals living in colder waters and
more turbulent environments tend to have
thicker shells and internal buttressing.
Unlike sea stars that use tube feet for
locomotion, sand dollars use their spines.
Young sand dollars ingest large sand grains
that act like a diver’s weight belt to help them
maintain position.