Tag Archives: Urchin

Invertebrate Locomotion in the Ocean

At the Catalina Island Marine Institute, we are all about being active and on the move.  The same goes for the invertebrates in our labs! But how do they move? Magic? Super powers? Thinking happy thoughts? Actually, we can explain with…..science!

Some of the animals in our lab move by using their little tube feet.  These are animals like the sea stars, sea cucumbers, and urchins, which are all members of the phylum Echinodermata.  Echinodermata translates to “spiny skin”.  Not only do the members of this phylum have spines, they also have sticky little feet! In fact, if you look underneath any of these animals, you will see what looks like little tubes with suction cups on the ends.  The animal will extend these tube  feet in the direction it wants to go, suction on, and then pull itself along.  Sometimes the tube feet can also be used as levers and for food capture. The tube feet can also be used to help the animal stay in place, if say, kids—I mean… “seagulls”—..were trying to grab at them! So cool.

Some of the friends in our Mollusk tank, such as the California Sea Hare, Aplysia californica, and the Spanish Shawl nudibranch, Flabellina iodinea, move in a different way.  These animals have a soft slug-like body, the length of which is called a “foot”.  Weird, I know, imagine if your whole body was called a foot! So the foot produces slime and when the animal contracts its muscles and moves tiny hairs on its body through the slime it manages to scoot, scoot, scoot! 

As if this wasn’t enough, many of the slugs can also swim (Fig.2)  The Spanish Shawl and the Lion’s Mane, Melibe leonina, can swim by whipping their head back and forth towards the end of  their foot. It can be an effective way to respond to predators, and kind of looks like they are throwing down for a dance off.

The take away here is that there are many ways to move through life, and invertebrates are great role models for showing us how it’s done! There’s no right or wrong way, whether you have many sticky feet, a whole body called a foot to scoot around on slime with, or maybe you just whip back and forth—- no kind of motion is too “loco” to be in the ocean!




The Keystone Species

Keystone Species are those of any organism that are considered crucial to the structure of the ecosystems in which they belong. The sea otter is an excellent example of a keystone species for the kelp forest ecosystem off the coast of California. Keystone species are important because they help promote biodiversity by controlling species that would otherwise dominate the biological community in which they reside. Also, these species can provide essential resources to other species within the community. Many keystone species are predators like a jaguar, but not all, some are herbivores like the African elephants in the savanna ecosystem.

Without keystone species present, the ecosystems would become dramatically different and many other species could be lost.



The term keystone refers to the center stone of a bridge that is wedge shaped and helps hold the others in place. If this stone is removed the entire bridge should collapse in on itself. The same idea goes for an ecosystem that loses a keystone species. Keystone species are so vital to the communities in which they belong because they are the stone that maintains the structure and function.

Keystone Species

An American zoologist Robert Paine was the first to coin the term keystone species back in 1966. While studying the rocky intertidal ecosystem in the Pacific Northwest, Paine observed dramatic changes to the biological community when the Starfish (Piaster ochraceus) was removed.

Of course, one of the most popular examples of a keystone species is the sea otter (Enhydra lutris) within the kelp forest ecosystem. As a member of the weasel family, the sea otter does not posses insulation in the form of thick blubber as many other marine mammals do. Instead the sea otter has an extremely high metabolism and the densest fur of any animal on the planet! The sea otter has such an appetite; it must consume 25 percent of its own body weight daily! Sea otters may appear cute and cuddly to humans, but they are actually voracious predators keeping the populations of invertebrates like sea urchins in check. They provide balance in the kelp forest by controlling the populations of invertebrates that feed upon the kelp.

Keystone species otter


Unfortunately, Russian fur traders sought after the pelts of the sea otters along the pacific coast of North America throughout the 17 and 1800’s. Eventually traders diminished the otter populations to the brink of extinction. This decimation wasn’t just trouble for the otters, the productive kelp forest ecosystems were greatly affected.

The populations of urchins within the kelp forest ecosystem expanded without sea otters as predator to keep the urchins from overpopulating. Sea urchins graze on the holdfasts of the kelp, and if gone unregulated, they can wipe out whole forests because the kelp can no longer anchor itself and simply floats away. This process can create desolate urchin barrens in areas that were once productive kelp forests. It’s not just the kelp itself that is impacted; there are over 800 species that rely on the kelp for food and habitat. Once the kelp is gone many species disappear with it, thus providing evidence that the sea otter is a vital keystone species.

keystone species water


keystone species urchin


Since the protection of sea otters, populations have increased in areas like Big Sur and Monterey Bay, California, but they still remain an endangered species. People are not sure if sea otter populations will ever fully recover, but hopefully we can learn from this important keystone species for future decisions facing ecosystems all over the world.

Written By: Chad Brewer


We would like to thank you for visiting our blog. Catalina Island Marine Institute is a hands-on marine science program with an emphasis on ocean exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and ocean happenings. This blog has been created by our staff who have at least a Bachelors Degree usually in marine science or related subjects. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science and ocean information. Feel free to leave comments, questions, or share our blog with others. Please visit www.cimi.org for additional information. Happy Reading!