Wildlife of the Week!

© Alexa Desautels. Several green sea urchins can be spotted; taken at the Shaw Centre for the Salish Sea.

This round of “Wildlife of the Week” we bring a fascinating creature into the spotlight. One might argue that the creature is even dressed for the occasion! Can you spot a green sea urchin (Strongylocentrotus droebachiensis) donning its spines with shell remnants? There are two others in the image, can you see them all? The green sea urchin, though it may be less obvious than the purple sea urchin in the Salish Sea, is an interesting member of the invertebrate community. Read on below to learn more about these fascinating critters!

This sea urchin can be differentiated from some more obvious others as it has fairly short spines; it also does not grow very large. The green sea urchin reaches a diameter of about 9 cm, however averages are usually smaller. The short spines only grow to a maximum of 2.5 cm long. The species is usually an overall green color, with its spines sometimes taking on red/brown or purple hues. This urchin has a more subtle appearance next to, say, urchins with longer and more defined spines like the purple or red sea urchins of the Salish Sea. 

The green sea urchin is a common invertebrate, stretching through large portions of the Northern Hemisphere, but not entirely around the globe. It makes its home on the West Coast from Alaska to northern Washington, and on the East Coast, it ranges from the Arctic to Cape Cod. It can also be located off the west coast of Russia and in some Atlantic seas of Europe. The green sea urchin can survive in depths of over 1100 m, but it can also be distributed at shallower depths, both in the intertidal zone and subtidal zones. They tend to prefer rocky sites with shelter from strong tidal surges, such as protected reefs and kelp beds. Although it may appear a sedentary animal, the green sea urchin is capable of navigating around its habitat. 

You might not believe me if I told you that a green sea urchin has five teeth and numerous feet on its underside. These tiny “tube” feet help the urchin to move its body around and locate food, or hide/escape from predators. These may also assist with grasping onto food. Other thin extensions of the body, called pedicellariae, may assist in surface cleaning, protection and food collection. These extensions have tiny claws at their ends. 

This urchin seeks out mostly vegetative matter for sustenance (like kelp) but may seek out other dead organic material or small creatures such as bryozoans or fish. When the urchin has selected a suitable food source, it can use its five teeth, arranged in a circle, to chop, tear and scrape food into its mouth. The urchin is an important member of the underwater community when kept in balance, but can also have a disastrous impact when in unnatural abundance. 

Sea urchins can destroy/eat entire kelp forests if their populations are not kept in check by natural predator systems, specifically sea otter predation. When sea otters faced drastic population decreases in the 1800-1900’s (due to excessive hunting from humans), “urchin barrens” devoid of kelp and much other life emerged. Fortunately in some regions of the West Coast, sea otter populations have been reintroduced and are recovering. Sea urchins’ predators can also include birds and lobsters. 

The green sea urchin follows a reproductive pattern that is common among many other marine invertebrates. When proper ocean ques emerge (e.g. temperature), both male and female urchins will both release their genetic material into the water via broadcast spawning. At fertilization, larvae will not immediately settle to the sea floor. They will drift as plankton for a time, entering various growth stages, before they settle to the substrate to become an adult. This will occur with the growth of larger and larger plates that make up the test (circular, calcareous body frame). The spines protrude from this central test. 

To humans, green sea urchins played and still play a role in some food systems. Sea urchins were a valued food source for many groups of Indigenous Peoples on both the West and East coasts in North America. Some groups ate the roe (reproductive organs) raw, or would consume the urchins boiled or roasted. The roe and eggs are today commercially and/or diver-harvested in some areas. The reason for this being that these components are considered a delicacy to a variety of cultures around the world. 

Unfortunately, the green sea urchin faces a changing fate with changing ocean conditions due to climate change and ocean acidification (which can greatly affect their shells). 

It is clear that the green sea urchin is a unique creature and can capture wonder and imagination with its impressive life history. To test your knowledge on the green sea urchin, try out some trivia below! 

  1. True or False? The green sea urchin breathes using a system that works like gills (ANS: True). 
  2. The green sea urchin is related to a sea star (ANS: True. Through Phylum Echinodermata). 
  3. Fill in the Blanks. The green sea urchin has an apparatus called “_____ Lantern”, which is actually the mouth system. (ANS: Aristotle’s). 

BONUS CHALLENGE: 

Why does the green sea urchin cover its body with shells and other materials? And how does it do this?

It uses its tube feet to hold tightly onto items in an attempt to better camouflage itself in the environment. 

Article Authored By: Alexa D., B.Sc./ Five Star Whale Watching. 

To learn more about this urchin, visit our References below!

Alaska Species Explorer.

Biodiversity of the Central Coast.

Memorial University.

Traditional Animal Foods of Indigenous Peoples of Northern North America.