Strongylocentrotus franciscanus

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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. ("Red Sea Urchins", 2013; Cowles, 2005; Kato and Schroeter, 1985)

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. (Cowles, 2005; Lawrence, 2007; Ricketts, et al., 1992; Tegner and Dayton, 1981)

  • Range depth
    10 to 90 m
    32.81 to 295.28 ft
  • Average depth
    30 m
    98.43 ft

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. ("Red Sea Urchins", 2013; Rogers-Bennett, 1994; Smith and Kroh, 2013)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    19 (high) cm
    7.48 (high) in

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. (Carefoot, 2013; Cowles, 2005; Kato and Schroeter, 1985; Khanna, 2005)

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. (Carefoot, 2013; Kato and Schroeter, 1985; Khanna, 2005)

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. (Cowles, 2005; Kato and Schroeter, 1985; Khanna, 2005)

  • Breeding interval
    The frequency of gamete release is unknown.
  • Breeding season
    Red sea urchins may spawn year-round or during warmer months, depending on location.
  • Average age at sexual or reproductive maturity (female)
    2 years
  • Average age at sexual or reproductive maturity (male)
    2 years

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. (Carefoot, 2013; Cowles, 2005; Nishizaki and Ackerman, 2005)

  • Parental Investment
  • no parental involvement
  • precocial

Lifespan/Longevity

Recent research using carbon-14 isotopes has suggested that individuals can live 100 years or more. ("Red Sea Urchins Found To Live Up To 200 Years", 2003; Whitehouse, 2003)

  • Range lifespan
    Status: wild
    200 (high) years
  • Typical lifespan
    Status: wild
    100 (high) years

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. (Kato and Schroeter, 1985; Lawrence, 2007)

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. (Lesser, et al., 2011; Marshall Cavendish Corporation, 2004; Nishizaki and Ackerman, 2005; Pisut, 2004)

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. ("Red Sea Urchins", 2013; Kato and Schroeter, 1985)

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. (Cowles, 2005; Duggins, 1983; Kato and Schroeter, 1985; Rogers-Bennett, 1994; Tegner and Dayton, 1981; Tegner and Levin, 1983)

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. (Cowles, 2005; Dean, et al., 1984; Kato and Schroeter, 1985; Rogers-Bennett, 1994; Shinn and Cloney, 1986; Tegner, 2001)

Commensal/Parasitic Species

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. ("Red Sea Urchins", 2013; Bureau, 2013; Rogers-Bennett, 1994)

  • 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. (Cowles, 2005)

  • 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. (IUCN, 2013; Kato and Schroeter, 1985; Rogers-Bennett, 1994)

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.

Glossary

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.

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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.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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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.

biodegradation

helps break down and decompose dead plants and/or animals

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

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.

crepuscular

active at dawn and dusk

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

herbivore

An animal that eats mainly plants or parts of plants.

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.

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

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).

macroalgae

seaweed. Algae that are large and photosynthetic.

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.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

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).

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.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

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).

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Oregon State University. 2003. "Red Sea Urchins Found To Live Up To 200 Years" (On-line). ScienceDaily. Accessed April 04, 2013 at http://www.sciencedaily.com/releases/2003/11/031106051646.htm.

2013. "Red Sea Urchins" (On-line). Accessed March 13, 2013 at http://marinebio.org/species.asp?id=45.

Bureau, D. 2013. "Pacific Urchin Harvesters Association Information" (On-line). Accessed April 03, 2013 at http://puha.org/assets/sea-urchin-fishery-information.asp.

Carefoot, T. 2013. "Sea urchins: Reproduction" (On-line). A Snail's Odyssey: A journey through the research done on west-coast marine invertebrates. Accessed December 28, 2013 at http://www.asnailsodyssey.com/LEARNABOUT/URCHIN/urchRepr.php.

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Dean, T., S. Schroeter, J. Dixon. 1984. Effects of grazing by two species of sea urchins (Strongylocentrotus franciscanus and Lytechinus anamesus) on recruitment and survival of two species of kelp (Macrocystis pyrifera and Pterygophora californica). Marine Biology, 78/3: 301-313. Accessed December 24, 2013 at http://link.springer.com/article/10.1007%2FBF00393016.

Duggins, D. 1983. Starfish predation and the creation of mosaic patterns in a kelp-dominated community. Ecology, 64/6: 1610-1619. Accessed December 24, 2013 at http://www.jstor.org/stable/1937514.

IUCN, 2013. "The IUCN Red List of Threatened Species. Version 2013.2" (On-line). Accessed December 28, 2013 at http://www.iucnredlist.org.

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Khanna, D. 2005. Biology of Echinodermata. India: Discovery Publishing House.

Lawrence, J. 2007. Sea Urchins: Biology and Ecology. Amsterdam: Elsevier.

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Ricketts, E., J. Calvin, J. Hedgpeth. 1992. Between Pacific Tides. Stanford: Stanford University Press.

Rogers-Bennett, L. 1994. Spatial patterns in the life history characteristics of red sea urchins, Strongylocentrotus franciscanus: Implications for recruitment and the California fishery. Davis, CA: University of California, Davis. Accessed December 24, 2013 at http://escholarship.org/uc/item/3m8833tq#page-5.

Shinn, G., R. Cloney. 1986. Egg capsules of a parasitic tubellarian flatworm: ultrastructure of hatching sutures. Journal of Morphology, 188/1: 15-28. Accessed December 28, 2013 at http://www.ncbi.nlm.nih.gov/pubmed/2422388.

Smith, A., A. Kroh. 2013. "The Echinoid Directory" (On-line). Natural History Museum. Accessed May 14, 2013 at http://www.nhm.ac.uk/research-curation/research/projects/echinoid-directory/.

Tegner, M., P. Dayton. 1981. Population Structure, Recruitment and Mortality of Two Sea Urchins (Strongylocentrotus franciscanus and S. purpuratus) in a Kelp Forest. Marine Ecology Progress Series, 5: 255-268. Accessed December 28, 2013 at http://www.int-res.com/articles/meps/5/m005p255.pdf.

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