Monday, November 2

Red Sea Urchin

Red Sea Urchins, British Columbia
The red sea urchins (Strongylocentrotus franciscanus) are colourful creatures,varying between a uniform red and dark burgundy, that crawl slowly over the sea bottom, using their spines as stilts. The sea urchin found in the Pacific Ocean from Alaska to Baja California. It lives in shallow waters from the low-tide line to 90 m (300 ft) deep, and is typically found on rocky shores sheltered from extreme wave action. 

Sea urchins belong to the marine invertebrate group called echinoderms or "spiny-skinned" animals. Close relatives of sea cucumbers and sea stars, they have spherical bodies, which are encased in a hard shell or "test", completely covered by many sharp spines. The species is large, with a maximum "test" diameter of over 18 cm and a maximum spine length of 8 cm. 

They occur on most rocky subtidal habitats of British Columbia from just below the low tide line to perhaps 90 m. Their preferred habitat is rocky ground with quantities of their food source of seaweeds and kelp. They avoid rocky areas exposed to extreme wave action and areas with sediments such as sand and mud. 

Feeding habits: This animal has a mouth with special jaws (Aristotle's lantern) located on the bottom (oral) surface. Its preferred diet is seaweeds and algae, which it scrapes off and tears up from the sea floor. During larval development, urchins use bands of cilia to capture food from the water column. Red sea urchins found in the channel adjacent to San Juan Island have been found to live a uniquely sedentary lifestyle with the heavy currents bringing an abundance of food. 

Fishery: Landings of red sea urchins from British Columbia have been recorded since 1978 and are shown in metric tons in Figure 3. Landings have increased rapidly during the 1980s until landings were reduced and stabilized by quotas in 1993. Fishing occurred exclusively in the south coast of British Columbia until 1983. The north coast of British Columbia was opened to fishing in 1984 and most landings since 1990 have come from the north coast. Fishery statistical areas where most landings have come from are areas 5 and 6 in the North and 12 and 13 in the south (Figure 4). Fishing occurs in less than 18 m depth by divers who use hand rakes to scoop their spiny catch into large mesh bags that are periodically hauled to the surface vessel. 

Behavior and reproduction: Sea urchins are often found living in clumps from five to ten. They have the ability to regenerate lost spines. Lifespan often exceeds 30 years, and scientists have found some specimens to be over 200 years old. 

Spawning peaks between June and September. Eggs are fertilized externally while they float in the ocean, and planktonic larvae remain in the water column for about a month before settling on the bottom of the sea floor, where they undergo metamorphosis into juvenile urchins. These juveniles use chemical cues to locate adults. Although juveniles are found almost exclusively under aggregated adults, the adults and juveniles are not directly related.

Information Source: 
Red Sea Urchin at a glance:
M. franciscanus
Binomial name
Mesocentrotus franciscanus (Aggasiz, 1863)
Strongylocentrotus franciscanus
Toxocidaris franciscana
Toxocidaris franciscanus
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