URCHIN RESEARCHIN’: SEA HEDGEHOGS OF THE REEF


Long-spined sea urchin Diadema antillarum (Melinda Rodgers / Dive Abaco)

URCHIN RESEARCHIN’: SEA HEDGEHOGS OF THE REEF

The long-spined sea urchin Diadema antillarum featured in this post is one of those creatures that handily offers its USP in its name, so you know what you are dealing with. Something prickly, for a start. These are creatures of the reef, and many places in the Caribbean and in the western Atlantic generally sustain healthy populations.

Long-spined sea urchin Diadema antillarum (Melinda Rodgers / Dive Abaco)

These animals are essentially herbivores, and their value to vulnerable coral reefs cannot be overstated. Where there is a healthy population of these urchins, the reef will be kept clean from smothering algae by their methodical grazing. They also eat sea grass.

Long-spined sea urchin Diadema antillarum (Melinda Rodgers / Dive Abaco)

HOW DO THE SPINES OF DIFFERENT KINDS OF URCHIN COMPARE?

Small sea urchins species have spines a few cms long at most. The long-spine variety exceed 10 cms, and the largest may have spines up to 30 cms (= 1 foot) long. The length, as shown here, means that when the creatures are safely lodged in crevices near their algae supply, their spines remain very visible.
Long-spined sea urchin Diadema antillarum (Melinda Riger / G B Scuba)
Anatomy of a long-spined sea urchin. You may possess a few of these organs yourself…

Long-spined sea urchin Diadema antillarum anatomy diagram (wiki)

Long-spined sea urchin Diadema antillarum (Melinda Rodgers / Dive Abaco)

CAN YOU GIVE US A TEST, PLEASE?

As with SAND DOLLARS and similar creatures, the skeleton of a sea urchin is known as a ‘test’. Urchin tests are remarkably beautiful, especially seen in sunlight. Here are 2 examples I photographed a while ago. You’ll immediately notice the delicate colours and the amazing complexity of the pattern and symmetry. The top one is (or is most like) a long-spined urchin test.
Long-spined sea urchin Test / Skeleton Diadema antillarum (Keith Salvesen / Rolling Harbour) Long-spined sea urchin Test / Skeleton Diadema antillarum (Keith Salvesen / Rolling Harbour)

A BIT ABOUT SYMMETRY

Sea urchins are born with bilateral symmetry – in effect, you could fold one in half. As they grow to adulthood, they retain symmetry but develop so-called ‘fivefold symmetry’, rather as if an orange contained 5 equal-sized segments. The graphic above gives a good idea of how the interior is arranged inside the segments.

Long-spined sea urchin Diadema antillarum (Melinda Rodgers / Dive Abaco)

A FEW FACTS TO HAND DOWN TO YOUR CHILDREN

  • Urchin fossil records date the species back to the Ordivician period, c 40m years ago
  • In the ’90s the population was decimated and still has not recovered fully
  • Urchins feel stress: a bad sign that the spines here are white rather than black
  • Urchins are not only warm water creatures: some kinds live in polar regions
  • Urchins are of particular use in scientific research, including genome studies
  • Some urchins end up in aquariums / aquaria, where I doubt the algae is so tasty
  • Kindest not to prod or tread on them
  • Their nearest relative (surprisingly) is said to be the Sea Cucumber 

Sea Cucumber (Melinda Riger / G B Scuba)

ARE THEY EDIBLE?

Apparently they are eaten in some parts of the world; their gonads and roe are considered a delicacy. As far as I know, they are not generally on the menu in the Bahamas. Correction invited. Personally, I could leave them or leave them.

CREDITS: Melinda Rodgers / Dive Abaco (1, 2, 3, 6, 9) taken Abaco; Melinda Riger / G B Scuba (4, 10, 11) taken Grand Bahama; Keith Salvesen / Rolling Harbour (7, 8) taken Abaco; Wiki graphic (5) taken from internet. RESEARCH Fred Riger for detailed  information; otherwise the usual magpie pickings…

Long-spined sea urchin Diadema antillarum (Melinda Riger / G B Scuba)

5 thoughts on “URCHIN RESEARCHIN’: SEA HEDGEHOGS OF THE REEF

  1. Absolutely fascinating! Really enjoyed this post, RH. The underwater photos, as always, are stunning–hats off to both Melindas. I enjoyed the facts, some of which were new to me (polar regions, wow; relative of the sea cucumber); and the Wiki graphic of the inside of a sea urchin is spectacularly interesting. Your two photos of the tests (a new meaning for me) are truly wonderful. You captured the perfect symmetry and astounding patterns in a most beautiful way. Thank you, RH.

    Liked by 1 person

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