Urchin Blues

Have you ever stood on a Sea Urchin ? Luckily I have not but from stories I have heard and stories from my own family I can assure you it is not on the top of my to-do list.

Sea Urchins or (Echinoidea using the scientific name) typically have 1 to 3cm long barbed spines which are 1- 2mm thick but are not lethal. I have heard it be compared to grabbing a rose bush or getting a sand spur stuck in your hand. The one exception of this being Diadema Antillarum which inhabits the Caribbean. This particular urchin has 10 – 30cm spines. This, I can only imagine, would be like getting stabbed with a sword and surprisingly merits Diadema Antillarums spines to be called “dangerous”. Probably one to avoid.

In my own mind I would never intentionally grab a rose bush so to me it seems clear that avoiding our spiky little friends is a given but I suppose accidents always happen. Imagine a typical tourist snorkeling around some rocks when something, a wave or a fish, causes him to grab on to a rock for comfort or to steady himself. Not paying intention he places his hand slap bang down onto Echinoidea and lo and behold, he has a handful of spines. This could cause more reaction of our imaginary tourist grabbing for the rock with the other hand and again finding a nice handful of spines. Quite a sight to behold I am sure but this is not the point of this essay so I move on.

Sea urchins inhabit every ocean on our planet and there are over 950 different species. This makes contact with homo sapiens inevitable but what has made the sea urchins so successful allowing them to live by the worlds beaches and up to depths of 5000 metres below the least explored part of our world, the sea. This I hope to get to the bottom off.

To even start this we have to step back in time. The first Echinoidea fossil was discovered in the Ordovician period (approximately 450 million years ago). To put this into perspective you and I first appeared on planet Earth 200,000 years ago. Saying this however, the fossil from 450 million years ago is not the sea urchin we know today. Today’s variant came along after the mass extinction before the Triassic period 252 million years ago. This mass extinction left only two lineages . The important lineage ,which we are interested in, is the Genus Miocidaris which has given rise to our modern day variety of sea urchins from an ancient ancestor.

This happened due to evolution, the principle first published by Mr Darwin and Wallace in 1858. Throughout the Jurassic and Cretaceous periods our spiky little friends came into existence as what we know them as today. This was due to adaptive breakthroughs which allowed them to very successfully exploit the habitats and food sources available to them at the time. In biological terms they successfully filled niches. So successful in-fact nothing else has usurped them and taken over. This is one argument of why they have done so well, the speed of which they evolved in the Jurassic and Cretaceous periods did not allow any other organism even a faint sniff of the habitats they coveted. They literally saw it, claimed it, changed and haven’t moved for over 145 million years. This seems a very effective method of staying alive, and why not, it worked !

So the evolutionary speed of the sea urchin seems to be a key clue as why it is still around today. And recently more evidence is supporting this claim as experiments by Morgan Kelly look to see the effects of rising CO2 in sea water on purple sea urchins of the California coast. In short the experiment has found that sea urchins can tolerate the higher levels of carbon dioxide due to natural selection (i.e survival of the fittest) which allows the sea urchins to evolve so all future offspring are tolerant of the higher carbon dioxide levels. (for more link at bottom of article)

Evolution speed is a key role for these porcupines of the sea it seems. Well it doesn’t seem it is pretty clear cut. This evolution speed has allowed concise ways of reproducing, breathing, moving and feeding which have allowed it to successfully stay in its respective niche and not be overthrown by a new young upstart.

So next time you see a sea urchin do not think of it as a spiky nuisance which could cause you 30 minutes of discomfort (or in Diadema Antillarum significantly more with its swords, I hope this never befalls you!) but think of the gigantic success story of this primitive looking beast. Appreciate its rapid evolution allowing it to be present on our planet for 145 million years, substantially more than you and I. I am not saying go up and give it a kiss but as I did in the Ionian sea only last week, just stop and look and move on. You could also eat one but after my first (and last tasting) it is like marmite. You either love it or hate it. I appreciate its ingenuity and rapid evolution but I can assure you I will be watching were I step when entering and exiting the water.

http://phys.org/news/2013-06-rapid-purple-sea-urchins-weapon.html