Geographic Range
Red sea urchins are predominantly found along the Pacific coast of North American,
from Isla Cedros, Baja California, to the Gulf of Alaska. This species is also found
along the northern coast of Japan.
- Biogeographic Regions
- nearctic
- palearctic
- pacific ocean
Habitat
Red sea urchins are among the dominant members of the communities that inhabit rocky
reefs from the low intertidal zone to about 90 m. As they feed primarily upon kelp,
these urchins tend to aggregate near kelp beds, avoiding areas that may be subject
to extreme wave action. When kelp and drift seaweed are abundant, red sea urchins
often stay in the same place, using their tube feet to keep a grip on their rocky
home as they feed. Juveniles may congregate beneath the spines of adults for protection
from predators and possibly food. However, when juveniles reach about 4 cm in diameter,
they venture out to acquire food across the rocky environment.
- Habitat Regions
- temperate
- saltwater or marine
- Other Habitat Features
- intertidal or littoral
Physical Description
Red sea urchins have spherically-shaped, calcareous shells called "tests," covered
by a thin epithelial tissue layer. Test coloration may range from light to dark purple,
while spines may be red, pink, light purple, dark purple, maroon, or brown. Tube feet
are normally dark red in color. They are the largest urchin species found on the Pacific
Northwest coast, with the largest recorded test diameters approaching 19 cm (7.5 in
in the very oldest specimens. A test is composed of ten fused exterior plates, which
are seamlessly connected by ambulacral zones. The entirety of the test is covered
by long, sharp spines that can measure up to 8 cm (3.1 in) in length, which are used
to deter predators and facilitate movement across the sea floor. Spines are attached
to the test by tubercles. Red sea urchins’ spines are particularly fine and do not
measure more than 1.27 cm (0.5 in) in diameter. There is a zone of external plates
on the test, which is closely associated with tube-feet and the water vascular system. In
urchins of this genus, a compound group of shell elements, called a polygeminate,
contains five to ten water vascular pores per plate. Plate zones that facilitate the
tube-feet and vascular system are known as ambulacra; in urchins of this genus, there
is a pattern of larger primary tubercles and lesser secondary tubercles on plates
separating the ambulacral zones, arranged in horizontal rows. The test has pores through
which tube-feet can extend. These tube-feet are part of the water vascular system
and can be retracted or further protruded by adjusting internal water pressure. Urchins
have an internal structure that behaves similarly to gills, functioning in locomotion,
feeding, and gas exchange. The primary feeding structure of the red urchin is "Aristotle's
Lantern." It is located on an urchin's oral surface, and bears many calcareous plates
and five teeth. This structure is also used to bore holes for the urchin to nestle
in.
- Other Physical Features
- ectothermic
- heterothermic
- radial symmetry
- Sexual Dimorphism
- sexes alike
Development
Fertilized eggs develop into planktonic larvae, known as echinoplutei, which go through
a number of stages of development over 6-10 weeks; time to settlement is largely dependent
on water temperature. Once settled, larvae undergo a rapid metamorphosis (lasting
no more than a week), resulting in a young urchin no more than 1 mm in diameter. Young
urchins tend to take refuge under the longer spines of adults until they reach 40
mm in diameter, at which point they leave the refuge of the adult's spines and forage
for food on their own. They reach sexual maturity at approximately 2 years of age
(diameter of 50 mm). Sexes are separate and there are no specific external characteristics
to distinguish sexes.
- Development - Life Cycle
- metamorphosis
Reproduction
Red sea urchins are broadcast spawners, releasing gametes into the water column where
fertilization occurs. Males release sperm into the water first, stimulating females
to release eggs.
- Mating System
- polygynandrous (promiscuous)
Red sea urchins reach sexual maturity within 1-2 years after completing metamorphosis.
Spawning seasonality varies between locations and appears to be affected by water
temperature and food availability. For example, urchins studied in Point Loma, CA,
spawn year-round, while in southern British Columbia, spawning reaches its peak between
June and September and during the spring and summer in Puget Sound. It is not known
how many offspring are produced per season, but higher numbers are produced when more
resources are available.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- year-round breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- broadcast (group) spawning
Although there is little active parental care exhibited, juveniles shelter under adults
until reaching larger sizes. Additionally, studies have shown that adults produce
chemical cues that attract juveniles when predators are present.
- Parental Investment
- no parental involvement
- precocial
Lifespan/Longevity
Recent research using carbon-14 isotopes has suggested that individuals can live 100
years or more.
Behavior
Although single individuals may be found, red sea urchins are typically found in aggregations
as a result of dietary and anti-predatory needs; these are stationary where food is
abundant and are more motile when food is scarce.
Home Range
Red sea urchins are not known to possess a defined home range, nor do they maintain territories.
Communication and Perception
The tube feet of red sea urchins are chemo-receptive, allowing them to detect food
sources and predators. Adults may release chemical cues, causing juveniles to take
shelter in the presence of predators. During spawning, females are able to sense when
males release gametes into the water.
Food Habits
Red sea urchins feed on kelp and seaweed including giant kelp (
Macrocystis pyrifera
) and bull kelp (
Nereocystis leutkeariu
). They scrape and bite food material with their Aristotle’s lantern, a five-toothed
structure. Movement facilitated by their tube feet allows them to search for food
when necessary. As planktonic larvae, echinoplutei consume zooplankton and adults
may consume plankton (particularly
Lithothamnion
sp. and
Bosiella
sp.) if other food sources are not available. They may even reabsorb their own tissues
if no other source of energy is present. Feeding rates are somewhat dependent on water
temperature, with an optimum feeding temperature of approximately 16°C.
- Primary Diet
-
herbivore
- algivore
- Animal Foods
- zooplankton
- Plant Foods
- algae
- macroalgae
Predation
Longer spines are an anti-predatory adaptation of these urchins. The tendency of juveniles
to shelter under the spine canopy of larger, mature individuals is also a protective
defense mechanism. Spiny lobsters (
Panulirus interruptus
) and California sheepshead (
Semicossyphus pulcher
) are two of the main predators of red sea urchins; both species are known to regulate
population density as well as the microhabitat distribution of sea urchin populations.
When sea otters (
Enhydra lutris
) are present, the effects of their predation on red sea urchin populations are dramatic,
rapid, and relatively predictable. Many species of starfish prey upon these urchins
as well; these animals may swallow red sea urchins whole or split the animals open
along their vertical axis. Rock crabs (
Cancer
spp.), horn sharks (
Heterodonuts francisci
), and wolf eels (
Anarrhichthys ocellatus
) are all known predators as well.
Ecosystem Roles
Red sea urchins are important in controlling the growth of kelp and seaweed species
on which they feed, influencing the structure of the kelp forest and its surrounding
benthic communities. Should population numbers rise, they can have devastating effects
on these species. They influence which species of marine algae will ultimately dominate
a given habitat. Their grazing can cause “barren grounds” in which no algae remain,
an issue of deforestation that has been increasing since 1993 and which negatively
influences species diversity. Red urchins also form cryptic microhabitats in kelp
holdfasts. Within temperate rocky reef habitats, red sea urchins create rocky pits
by boring holes in the substrate, possibly exacerbating bioerosion. They are even
known to bore holes into metal pier pilings. Their bodies, under protective spine
canopies, function as microhabitats; small fishes and invertebrates, as well as juvenile
urchins, avoid predation and violent wave action under their protection. Red sea urchins
compete with other species, such as purple sea urchins (
Strongylocentrotus purpuratus
) and green abalone (
Haliotis fulgens
) for habitat space and specific food items. Red sea urchins also serve as hosts to
numerous commensal species including flatworms, copepods, and amphipods.
- Ecosystem Impact
- creates habitat
- biodegradation
- Colidotea rostrata (Class Malacostraca , Phylum Arthropoda )
- Dulichia rhabdoplastis (Class Malacostraca , Phylum Arthropoda )
- Syndisyrinx franciscana (Class Rhabditophora , Phylum Platyhelminthes )
Economic Importance for Humans: Positive
Although the red sea urchin fishery has developed relatively recently (since the 1980’s),
it experienced a period of exploitation followed by a leveling off of harvesting effort.
Red sea urchin is of such high commercial interest because of its gonads, referred
to as "roe" or "uni", which are considered a delicacy in many markets. The highest
quality roe from either male or female urchins is collected between October and May
because later months yield inferior tissues as the urchins begin to spawn.
- Positive Impacts
- food
Economic Importance for Humans: Negative
There are no known adverse effects of red sea urchins on humans outside of potential
injury by their spines if handled roughly by divers or fishers.
- Negative Impacts
-
injures humans
- bites or stings
Conservation Status
Although this species has not yet been evaluated by any agency for potential conservation,
red sea urchin abundance has been progressively dwindling since the 1970s. Fishing
pressure may be an important variable in determining urchin populations and distribution,
in addition to expected species competition for space and nourishment. Little research
has been done regarding the role that humans may play in this species' need for conservation;
as of 2013, the fact that California has perpetually deficient funds to invest in
sea urchin research has meant that the qualities of urchin statistics are unlikely
to improve within the next decade. This dilemma is especially problematic in terms
of red sea urchin research, due to the potential sub-populations that exist within
this species. Annual harvest of red sea urchins in southern California produces approximately
4.5 million kg (10 million lbs) of legally accumulated, marketable urchin gonads.
This amount has been decreasing since 1990 due to decline in available catch beginning
as early as 1985. Although this decline has caused fishermen to change or decrease
the exploitation of this biological resource, revival will be slow due to less breeding
individuals. In northern California, rapid growth catch to 30 million lbs in 1988
plummeted to a mere 5 million lbs by the 1990s.
Additional Links
Contributors
Emily Bartholomew (author), San Diego Mesa College, Elena Hursky (author), San Diego Mesa College, Paul Detwiler (editor), San Diego Mesa College, Jeremy Wright (editor), University of Michigan-Ann Arbor.
- Nearctic
-
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Palearctic
-
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Pacific Ocean
-
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- temperate
-
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
- saltwater or marine
-
mainly lives in oceans, seas, or other bodies of salt water.
- benthic
-
Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.
- reef
-
structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.
- coastal
-
the nearshore aquatic habitats near a coast, or shoreline.
- intertidal or littoral
-
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- heterothermic
-
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
- radial symmetry
-
a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).
- metamorphosis
-
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
- polygynandrous
-
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
- iteroparous
-
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
- seasonal breeding
-
breeding is confined to a particular season
- year-round breeding
-
breeding takes place throughout the year
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- external fertilization
-
fertilization takes place outside the female's body
- young precocial
-
young are relatively well-developed when born
- diurnal
-
- active during the day, 2. lasting for one day.
- nocturnal
-
active during the night
- crepuscular
-
active at dawn and dusk
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- solitary
-
lives alone
- colonial
-
used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
- zooplankton
-
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
- macroalgae
-
seaweed. Algae that are large and photosynthetic.
- biodegradation
-
helps break down and decompose dead plants and/or animals
- food
-
A substance that provides both nutrients and energy to a living thing.
- herbivore
-
An animal that eats mainly plants or parts of plants.
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