Red Sea Urchins, Mesocentrotus franciscanus
Taxonomy Animalia Echinodermata Echinoidea Camarodonta Strongylocentrotidae Mesocentrotus franciscanus
Description & Behavior
Red sea urchins, Strongylocentrotus franciscanus (A. Agassiz, 1863), are colorful creatures, varying between a uniform red and dark burgundy, that crawl slowly over the sea bottom using their spines as stilts. Sea urchins belong to the marine invertebrate group called echinoderms or "spiny-skinned" animals. They are close relatives of sea cucumbers. The red sea urchin is the largest of the sea urchins, with a maximum "test", or outer skeleton, diameter of more than 18 cm and a maximum spine length of 8 cm. Their test is made up of 10 fused plates that encircle the sea urchin like the slices of an orange. Every other section has holes through which the sea urchin can extend its tubed feet. These feet are controlled by a water vascular system. By changing the amount of water inside, the animal can extend or contract the feet. Sea stars move around the same way.
World Range & Habitat
They occur on most rocky subtidal habitats 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, mud and gravel.
Feeding Behavior (Ecology)
Red sea urchins graze on attached or drift seaweed and kelp using their mouths which are located on the ventral (under) surface of the animal. They have specialized jaws consisting of 5 teeth used to devour plant material. They use their tube feet to hold on to the bottom while feeding, but they can move rather quickly using their feet, spines, or even their teeth.
Sea urchins are often found in aggregations whose combined feeding activities can remove all large plant material in an area.
Sea urchins are readily eaten by some fish (e.g., wolf eels), sea stars and crabs, although large adults appear to be less susceptible to predation by virtue of their size and have few predators. Sea otters, however, will eat even the largest sea urchins cracking them open on rocks.
The spawning of red sea urchins peaks between June and September in southern British Columbia. The fertilized eggs develop into planktonic larvae before settling on the bottom where they change into tiny juvenile sea urchins. This replenishment of the population, or "recruitment", appears to occur annually in local waters. New recruits must hide from potential predators and many seek shelter under the spines of adult sea urchins which have a test diameter of 9.5 cm or larger. Young sea urchins emerge from shelter when approximately 4 cm in diameter and forage freely over the rocky sea bottom. Adulthood is attained at approximately 5 cm diameter and legal size of 10 cm is reached in 4-5 years. Their life span is reported to be over 100 years.
Conservation Status & Comments
You could call sea urchins the porcupines of the sea. Like a porcupine's quills, sea urchins depend on their long spines to deter predators. In fact, the sea urchin gets its name from an Old English word for the spiny hedgehog, a land animal similar to the porcupine. Most sea urchins can be carefully handled by humans without harm, however the poisonous spines of the long-spined sea urchins found in south Florida and elsewhere can penetrate human skin and break off causing infection and, in some cases, the need for surgical removal of spine fragments. Harmless varieties like the purple and green sea urchins are more common in cooler waters.
References & Further Research
Research Mesocentrotus franciscanus » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SCIRIS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
Feedback & Citation
Start or join a discussion about this species below or send us an email to report any errors or submit suggestions for this page. We greatly appreciate all feedback!
Help Protect and Restore Ocean Life
Help us protect and restore marine life by supporting our various online community-centered marine conservation projects that are effectively sharing the wonders of the ocean with millions each year around the world, raising a balanced awareness of the increasingly troubling and often very complex marine conservation issues that affect marine life and ourselves directly, providing support to marine conservation groups on the frontlines that are making real differences today, and the scientists, teachers and students involved in the marine life sciences. Join us today or show your support with a monthly donation.
With your support, most marine life and their ocean habitats can be protected, if not restored to their former natural levels of biodiversity. We sincerely thank our thousands of members, donors and sponsors, who have decided to get involved and support the MarineBio Conservation Society.