All About the Sea Urchin

Sea Urchins belong to the group known as “Echinoderms” and globally there are about 200 different species found in the oceans.  Preferring warm water, Sea Urchins can be found on the rocky bottom of the sea or close to coral reefs.  They have a general lifespan of up to 30 years in the wild, however, the Red Sea Urchin has the longest lifespan of all and can live up to 200 years!!

A Unique Body

Depending on the species, Sea Urchins are between 1.2 to 3.9 inches in diameter, with a globe-like shape to their bodies.  Their soft insides are covered in a hard shell with long spines.  Sea Urchins have a radial symmetry and can be divided into five equal parts while the colour of the Sea Urchin depends on the species.  A large majority of Sea Urchins are black, purple, brown, green or red.  Scattered among the spines on the Sea Urchin are claw-like structures for the purpose of protection from predators.  Certain Sea Urchins have venom in the spikes.

Underneath the Sea Urchin, they have five rows of feet with suckers on the end of them which help to keep them stuck on rocks or to move on the ocean floor.  Sea Urchins are omnivores and feed on plankton, algae and seaweed.  “Aristotle’s Lantern” is what the Sea urchins mouth is called.  The mouth has five sharp teeth that are able to drill a hole in a rock.


Sea Urchins mate in the spring and like many sea creatures they reproduce by releasing eggs and sperm cells in the water.  This is known as external fertilization.   Before it becomes a Sea Urchin it goes through a larvae stage and swims with other tiny sea animals as a part of zooplankton.

Sea Urchins have many predators, regardless of its spines.  Seabirds, fish and crabs are all predators of the Sea Urchin.  There is a drastic decline in the Sea Urchin population in the wild and pollution in the sea and overfishing may mean that they are soon placed on the endangered list.

The Southwest Cape once had an abundance of Sea Urchins but in 1994 they mysteriously started disappearing.  After investigation, it was found that Rock Lobsters numbers had increased and they were devouring the Urchins.  This had a ripple effect on the many other sea creatures and more importantly, it had a severe impact on the abalone in the area.  Sea Urchins provide nurseries for the abalone and abalone have commercial value.  The juvenile abalone are protected from octopus and rock lobsters by hiding in the spines of the Sea Urchin.  Without Sea Urchins, predators were feasting on the young abalone.

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