Purple Sea Urchin
Strongylocentrotus purpuratus
Purple sea urchins are often found in the intertidal zone. Their primary predators, sea otters and sea stars, have become drastically reduced due to over fishing and wasting disease. While purple sea urchins have been subject to mass die off before, their numbers have jumped due to the lack of predators in recent years. This has resulted in ‘urchin barrens’, where the urchins have stripped away kelp forests with their insatiable appetites.
SPECIES IN DETAIL
Purple Sea Urchin
Strongylocentrotus purpuratus
CONSERVATION STATUS: Safe for Now
CLIMATE CHANGE: Vulnerable
At the Aquarium
- Baja California
- Northern Pacific
- Coastal Corner Touch Pool
Geographic Distribution
Alaska to Baja California, Mexico
Habitat
Purple sea urchins are primarily found in shallower waters and are in the intertidal zone. They have been found at depths of 152 meters (500 feet).
Physical Characteristics
These sea urchins live up to their name by having a lovely purple color. Their round bodies (called tests) can grow up to 10 centimeters (4 inches) and are covered in spines. Younger urchins are pale green with purple tipped spines.
Purple sea urchins also have tube feet that end in suction cups that help them hold onto rocks and other hard surfaces and move around.
Purple sea urchins belong in a Phylum called ‘echinoderms’ which is based on the Ancient Greek words of ‘echinos’ (hedgehog) and ‘derm’ (skin).
Echinoderms, which also include sea stars, have five point radial symmetry. While not immediately obvious when looking at the top of a live sea urchin, their body is divided into five sections.
Size
Purple sea urchins can grow to 4 inches (10 centimeters) in size.
Diet
Purple sea urchins are grazers. Urchins have a special mouth, called an Aristotle’s Lantern, that helps them scrape algae off of rocks and chew on various macro algae, especially giant kelp. Their mouth has five bony teeth which is very effective at chewing algae. They are often found in kelp forests gnawing away at kelp holdfasts.
Reproduction
Purple sea urchins can start to reproduce between one to two years of age and generally reproduce between January through March. They have an opening at the top of their body that allows them to secrete eggs or sperm. The male and female urchins will release their gametes into the water column, which will merge together as a fertilized egg and settle to the substrate to grow into an urchin.
Behavior
Aside from spines to protect themselves, and tubed feet to move around, Purple Sea Urchins also have pedicellariae, which are long stalks with a pincher at the end. These pinchers help the urchin defend itself from attackers and keep sponges and barnacles from growing on their body.
Using its strong teeth, purple sea urchins can bore their way into a rock, creating a depression. If the urchin stays in their hole long enough, it will get too big to leave the hole it created and be trapped there.
Adaptation
The purple sea urchin’s tube feet not only help with moving around, but they also assist with respiration and sensory input.
During low tide, purple sea urchins will ‘decorate’ themselves with bits of shell, rock and algae to protect and camouflage themselves.
Longevity
Purple sea urchins may live up to 70 years
Conservation
Purple sea urchins have a high mortality rate above 73 degrees Fahrenheit (22 degrees Celsius), so rising temperatures may threaten urchins and drive them from shallower areas.
Special Notes
The genome of the purple sea urchin was completely sequenced. Urchins share a common ancestor with human beings, so by reviewing the purple sea urchins’ genomes, we can learn more about humans.
- Humans eat the roe of purple sea urchins; you can order it at a sushi restaurant. It is commonly known as “uni”.
- Sea otters love purple sea urchins so much that if they eat enough purple sea urchins, the sea otters’ skeletons turn purple.
SPECIES IN DETAIL | Print full entry
Purple Sea Urchin
Strongylocentrotus purpuratus
CONSERVATION STATUS: Safe for Now
CLIMATE CHANGE: Vulnerable
- Baja California
- Northern Pacific
- Coastal Corner Touch Pool
Alaska to Baja California, Mexico
Purple sea urchins are primarily found in shallower waters and are in the intertidal zone. They have been found at depths of 152 meters (500 feet).
These sea urchins live up to their name by having a lovely purple color. Their round bodies (called tests) can grow up to 10 centimeters (4 inches) and are covered in spines. Younger urchins are pale green with purple tipped spines.
Purple sea urchins also have tube feet that end in suction cups that help them hold onto rocks and other hard surfaces and move around.
Purple sea urchins belong in a Phylum called ‘echinoderms’ which is based on the Ancient Greek words of ‘echinos’ (hedgehog) and ‘derm’ (skin).
Echinoderms, which also include sea stars, have five point radial symmetry. While not immediately obvious when looking at the top of a live sea urchin, their body is divided into five sections.
Purple sea urchins can grow to 4 inches (10 centimeters) in size.
Purple sea urchins are grazers. Urchins have a special mouth, called an Aristotle’s Lantern, that helps them scrape algae off of rocks and chew on various macro algae, especially giant kelp. Their mouth has five bony teeth which is very effective at chewing algae. They are often found in kelp forests gnawing away at kelp holdfasts.
Purple sea urchins can start to reproduce between one to two years of age and generally reproduce between January through March. They have an opening at the top of their body that allows them to secrete eggs or sperm. The male and female urchins will release their gametes into the water column, which will merge together as a fertilized egg and settle to the substrate to grow into an urchin.
Aside from spines to protect themselves, and tubed feet to move around, Purple Sea Urchins also have pedicellariae, which are long stalks with a pincher at the end. These pinchers help the urchin defend itself from attackers and keep sponges and barnacles from growing on their body.
Using its strong teeth, purple sea urchins can bore their way into a rock, creating a depression. If the urchin stays in their hole long enough, it will get too big to leave the hole it created and be trapped there.
The purple sea urchin’s tube feet not only help with moving around, but they also assist with respiration and sensory input.
During low tide, purple sea urchins will ‘decorate’ themselves with bits of shell, rock and algae to protect and camouflage themselves.
Purple sea urchins may live up to 70 years
Purple sea urchins have a high mortality rate above 73 degrees Fahrenheit (22 degrees Celsius), so rising temperatures may threaten urchins and drive them from shallower areas.
The genome of the purple sea urchin was completely sequenced. Urchins share a common ancestor with human beings, so by reviewing the purple sea urchins’ genomes, we can learn more about humans.
- Humans eat the roe of purple sea urchins; you can order it at a sushi restaurant. It is commonly known as “uni”.
- Sea otters love purple sea urchins so much that if they eat enough purple sea urchins, the sea otters’ skeletons turn purple.