Red Sea Urchin
| Red Sea Urchin | ||||||||||||||||||
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 Red Sea Urchin.
(PD) Photo: Michael Nishizaki | ||||||||||||||||||
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| Binomial name | ||||||||||||||||||
| Strongylocentrotus franciscanus (A. Agassiz, 1863) |
The Red Sea Urchin, Strongylocentrotus franciscanus (A. Agassiz, 1863), is a species of marine invertebrate belonging to the phylum Echinodermata or "spiny-skinned" animals. Typically found in the Pacific ocean from Alaska to Baja California, red urchins inhabit shallow waters from the low-tide line to depths of 100 m. In general, this species prefers wave-sheltered rocky shorelines.
Physical Description
During larval development, the body of a sea urchin transitions from radial to bilateral symmetry. This bilaterally symmetrical larva, called an echinopluteus, subsequently develops a type of pentaradiate symmetry that characterises echinoderms. As adults, the body, or test, can reach up to 24 cm and can vary in colour from red to dark burgundy. The test is covered by sharp spines that can grow up to 8 cm. Among the spines are rows of tiny tube feet each terminating with a suction cup. In addition, the body is also covered with small pincer-like structures called pedicellaria.
The mouth of an urchin, called the Aristotle's lantern, consists of 5 teeth and is located on the underside (or oral) of the body. Waste is excreted from an opening on the upper side (or aboral) of the body. During reproduction, eggs and sperm are also released from the aboral side of the body through 5 small openings called gonopores.
Feeding Habits
Red urchins will eat a wide range of foods, both plant and animal though brown kelp is the preferred food item. In the Pacific Northwest, urchins preferentially graze bull kelp (Nereocystis leutkeana)[1], whereas in southern California, Macrocystis is preferred [2]. During larval development, urchins use bands of cilia to capture food from the water column [3].
Behavior and reproduction
Lifespan in red urchins often exceeds 30 years, and recent evidence indicates that some individuals are over 100 years old.[4]. Urchins are known as broadcast spawners, where gametes are released into the water and fertilization occurs in the water column. Spawning peaks between June and September and planktonic larvae (echinopluteus) remain in the water column for about a month before settling on the bottom of the sea floor. Once settled, larvae undergo metamorphosis into juvenile urchins. Aggregations of adult urchins provide a "spine canopy" that provides protection for juveniles from predation and extreme water motion[5]. In fact, juveniles are found almost exclusively underneath adults [6] until they reach a test diameter of 40mm.
[7] and may utilize chemical cues to locate adults[8]. Although juveniles are found almost exclusively under aggregated adults, the adults and juveniles are not necessarily related [9].
Similar species
There are two congeneric species generally found living in the same habitats as the red urchin. The purple urchin, Strongylocentrotus purpuratus is smaller, with shorter spines and a deep purple color. Purple urchins are usually found in slightly shallower and more wave-exposed areas. The second species is the green urchin Strongylocentrotus droebachiensis, which is smaller than the red urchin and has shorter and thinner spines.
Fishery
Red sea urchins are primarily harvested for their reproductive organs, or "roe,". Most sea urchin roe is exported to Japan where it is used as an ingredient in sushi. Harvested in California since the 1970's, sea urchin the fishery and expanded until is was the second most valuable fishery in California.
References
- ↑ Vadas R.L. 1977. Preferential feeding: An optimization strategy in sea urchins. Ecological Monographs 47: 337-371.
- ↑ Leighton D.L. 1966. Studies of food preference in algivorous invertebrates of Southern California kelp beds. Pacific Science 20: 104-113.
- ↑ Strathmann, R 1971. The feeding behavior of planktotrophic echinoderm larvae: mechanisms, regulation, and rates of suspension feeding. Journal of Experimental Marine Biology and Ecology 6: 109–160.
- ↑ Ebert, TA and JR Southon 2003. Red sea urchins can live over 100 years: confirmation with A-bomb [14.sup]carbon - Strongylocentrotus franciscanus. Fishery Bulletin, 101(4): 915-922.
- ↑ Nishizaki MT and JD Ackerman 2007. Juvenile–adult associations in sea urchins (Strongylocentrotus franciscanus and S. droebachiensis): protection from predation and hydrodynamics in S. franciscanus). Marine Biology 151:135-145.
- ↑ Low, CG 1975. The effect of grouping of Strongylocentrotus franciscanus, the giant red sea urchin, on its population biology. Ph.D. thesis, University of British Columbia, Vancouver, BC.
- ↑ Tegner MJ and PK Dayton 1977. Sea urchin recruitment patterns and implications of commercial fishing. Science 196: 324-32.
- ↑ Nishizaki, MT & JD Ackerman 2005. A secondary chemical cue facilitates adult-juvenile associations in red sea urchins (Strongylocentrotus franciscanus). Limnology & Oceanography 50(1): 354-362.
- ↑ Moberg, PE & RS Burton 2000. Genetic heterogeneity among recruit and adult red sea urchins, Strongylocentrotus franciscanus. Marine Biology 136:773-784.