The Porcupines of the Sea

November 28, 2021

By Camryn Anderson | Education Intern

At the Conservancy of Southwest Florida, our Dalton Discovery Center is home to many native aquatic and terrestrial animals. When visiting the Dalton Discovery Center, you are sure to be wowed by a dazzling variety of snakes, adorable baby alligators, unique fish, and all of the additional excitement that is found around the twist and turns of our exhibits.

One particular aquatic tank that keeps many coming back time and time again is the Touch Tank!

This exhibit allows guests to get hands on and personal with some real-life aquatic invertebrates, including an often overlooked species – the sea urchin!

The Importance of Sea Urchins

In the wild, sea urchins live in very diverse habitats. They are located as far deep as 180 feet in the ocean and as shallow as inter-tidal pools. In each varying depth, urchins can be found in a range of terrain from sandy bottoms, seagrass beds, and underneath red mangrove trees. Typically, these invertebrates live in large groups called “urchin beds.”

Camryn holding a pencil urchin

Sea urchins range in size from about 3 cm to 10 cm and are all generally spherical in shape. The spines on the outside of an urchin have many functions. They are used for camouflage, protection, and grabbing food. Some sea urchins have venomous spines, but not the ones in our touch tank!

Sea urchins perform the thankless yet vital job of maintaining the balance between corals and algae.

Coral actually gets their colors from internal beneficial algae. When coral becomes stressed due to an unhealthy environment, they expel their good algae, thereby losing their color and becoming what is known as bleached. The corals then become attacked by harmful external algae that grows quickly on their white skeletons, preventing their ability to recover from bleaching.

Sea urchins graze and feed on these algae. Without urchins, coral reefs would be in even more danger of being completely suffocated by detrimental algae. Additionally, sea urchins are a vital food source for some predators.

Without urchins, animals across the globe like sea otters, spiny lobsters, and triggerfish would likely decline due to this missing staple in their diet.

Urchin Anatomy

You may look at these spiny creatures and ask yourself, “Where is their mouth?” Sea urchins have an eating structure called Aristotle’s Lantern.

This structure is made of five hard plates that come together like a beak and is located on the underside of the urchin.

This beak-like mouth scrapes the algae off coral and other formations, such as rocks and dock pilings.

Another incredible feature of the sea urchin is their water vascular system.

This organ functions within their tube feet, which are numerous thin projections that extend from the urchin.

These tube feet carry out respiratory, excretory, and some circulatory functions, as well as helping urchins move around.

At the Touch Tank

The Dalton Discovery Center is currently home to a sea biscuit, as well as some pencil urchins and decorator urchins. Some of our pencil urchins live full time in our touch tanks since their spines are blunt and safe to touch. We feed our urchins a variety of foods such as algae wafers, a homemade fish diet mixture, and small pieces of fish and/or shrimp.

Additionally, we attach cut vegetables to rocks in their tanks in order to provide enrichment. This activity simulates the sea urchins’ natural foraging habits. It is always very interesting to watch them move the food pieces along their spines down to their mouth underneath.

Sometimes, you get lucky and get to see them attached to the glass. When this happens, you can even see their beak scraping off food. Their enclosures are regularly maintained through water changes, scrubbing, and water quality checks to make sure chemical levels are stable and suitable for their survival. When the salt water is flowing into the tank, sometimes you can notice them extending their tube feet into the clean running water.

Despite these critters being brainless, spineless, and mysterious looking, sea urchins serve a vital role in protecting coral reefs, being a food source for certain carnivores, and maintaining algal balance in our waters.

Here at the Conservancy, we aim to highlight these essential attributes by providing a hands on opportunity to learn more about these cool critters. Come and visit us to discover these marvelous species firsthand!


CK-12 Foundation

Florida Weekly

Reef Resilience Network

Tree of Life Web Project

Woods Hole Oceanographic Institution

World Wildlife Fund