Green sea urchins (Strongylocentrotus droebachiensis) inhabit the Arctic regions of both the Atlantic and Pacific Oceans. On the east coast of the U.S., they range as far south as New Jersey, and they reach down to Puget Sound on the west coast. This species usually reside in the rocky intertidal area to 30 ft.(9 m), but they inhabit depths up to 3,770 ft. (1,150 m).
Like other echinoderms (such as the sea star and sand dollar), sea urchins are radially symmetrical and divided into five parts. Green sea urchins have a hard outer covering called a “test.” Tube feet and spines cover the surface of the test. The spines are jointed at the base, and the urchin moves by using its tube feet and lower spines. The green sea urchin’s spines are short and sharp, and they are more delicate than the spines of many other species.
An urchin’s mouth is centered on its underside surface, and it is surrounded by a complex feeding structure called Aristotle’s lantern. This structure boasts extensive musculature and five sets of triangular plates or teeth. These teeth allow the urchins to graze on tough algae, their favorite food. A sea urchin’s anus is located on the top of the animal.
Sea urchins are either male or female, and they mate by broadcasting their eggs and sperm into the water. They use environmental triggers such as temperature or daylight to time the release of their gametes and increase the chance of fertilization. The fertilized eggs develop into larvae and resemble tiny upside-down jellyfish. The larvae soon settle to the bottom and remain hidden to avoid predation.
Sea stars, crabs, wolf eels, other large fish, and sea otters are the main predators of green sea urchins.
Many cultures consider sea urchin eggs a delicacy, and both green and red sea urchins are commercially harvested in small fisheries in Alaska. Red sea urchins (Mesocentrotus franciscanus) grow larger and have a more southerly range than green sea urchins. Both species live near Kodiak, but the green urchins are more common. Harvesting sea urchins is both expensive and labor-intensive. Divers using either scuba gear or surface-supplied air handpick the urchins and place them in mesh bags. When the bags are full, they are lifted to the surface. The expense of harvesting, difficulties in marketing, and the uneven distribution of urchins limit the urchin fishery in Alaska.
Sea stars are the royalty of the echinoderm world, and I covered them a few years ago in this post. I am happy to note that the sea stars near us slowly seem to be recovering from sea-star wasting syndrome. You can read my post about the syndrome here.
In my next post, I will cover sand dollars. Various species of echinoderms species look very different from each other, but when you peel away the layers, you can see their similarities.
Robin Barefield is the author of five Alaska wilderness mystery novels: Big Game, Murder Over Kodiak, The Fisherman’s Daughter, Karluk Bones, and Massacre at Bear Creek Lodge. She is also the author of the non-fiction book Kodiak Island Wildlife. Sign up below to subscribe to her free, monthly newsletter on true crime and mystery in Alaska, and listen to her podcast, Murder and Mystery in the Last Frontier.
Enjoy a poem from Steve Levi’s new book, Bonfire Saloon.
