Sea Creature Feature of the Week: Purple Sea Urchin
By: Shannon Campbell
This spiky invertebrate is a purple sea urchin. They may be found around the rocky coastlines of the Pacific and Atlantic oceans, built to endure the harsh conditions of a rocky intertidal environment.
Purple sea urchins are members of the phylum Echinoderms, which includes sea stars, sea cucumbers, and other organisms. They have a five-part symmetry known as pentaradial symmetry. This simply indicates that the body may be split into five distinct portions, each of which is equal. As a foraging omnivore, purple sea urchins only grow to be around 3 inches long and primarily eat red, brown, and green algae. They are an essential prey item for animals such as sea stars and sea otters, as well as a sushi delicacy.
What you would not anticipate is for these animals to be able to walk. Purple sea urchins move over the bottom and attach themselves to surfaces with their tube feet. The urchin breathes through its own feet as well. The tube feet are part of the sea urchinscirculatory system and function similarly to a hydraulic system. Water is pumped into the tube feet as the muscles flex, pushing the feet outwards. When the muscles relax, the feet retract.
Purple sea urchins graze on kelp in the Pacific and are partly to blame for the destruction of kelp forests in Northern California. A sea-star die-off in California waters is linked to a population increase. Sea urchin activity may often be used to detect changes in water parameters and quality in conservation initiatives. Stress symptoms include a lack of activity and drooping spines, and they are among the first creatures to exhibit stress during algal blooms, out-of-season temperature fluctuations, and dirty water.