May 14, 2006
Like a canary in a mine, sea urchins are indicator species, being sensitive to environmental pollution. The Green Sea Urchin, Strongylocentrotus droebachiensis, is common is clean sub-tidal rocky environments along the North Atlantic coast of Europe and North America. They appear to be making a come-back in the previously filthy, urchin-depleted waters of America’s first harbor, Boston, Massachusettes.
Like their more familiar cousins the star-fish and sand-dollar, sea urchins are echinoderms, having five-sided radial symmetry, a water-vascular system ending in podia (sucker-like tube feet), which provide locomotion, and a plated endoskeleton. Echinoderms are benthic (bottom-dwelling), macroscopic marine organisms with a larval planktonic stage. Within a coelom (fluid-filled body cavity), sea urchins have large gonads, which are a popular Asian delicacy and account for their cash value as a marine food item. Crabs, sea stars, and eels also enjoy munching on them. Sea urchins consume kelp and scrape algae from hard surfaces using a 5-toothed apparatus first described by the philosopher-naturalist Aristotle in about 350 B.C.E. -- he likened this creature to a lantern. Subsequently, this apparatus, which is unique in the animal kingdom, has been called “Aristotle’s Lantern” and is frequently used to identify fossilized sea urchin specimens, some as old as 200 million years.
The healthy Green Sea Urchin shown above is displaying his (or her--they have separate sexes) Aristotle’s Lantern -- it's being held upside-down. This specimen had just been caught in a lobster trap where it was scraping algae. The lobster trap was pulled from just off Rainsford Island, in the heart of Boston’s previously urchin-depleted harbor, another indicator of the surprising success of the two-decade Boston Harbor environmental recovery program.Related Links: