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Wednesday, March 23, 2011

The strangely touching case of the brittle star and the coral, or: why I was crying at my desk yesterday

There are a lot of things that touch your heart and in doing so generate warm feelings and misty eyes. Puppies. Old faded photographs (especially if they are of puppies). Old videos of Puppy Bowl. And so on.

You know what's not on that list? Brittle stars. For the vast majority of humanity, brittle stars score a perfect zero on the emote-o-scale. An average person sees a brittle star, and they think "I don't care". They may even say it out loud.

See? You just said it, didn't you?
In fact, I personally guarantee that the amount of human emotion generated by dropped ice cream during the year 2010 is orders of magnitude greater than the amount that has been generated by brittle stars throughout all of human history. 

And you know what? That's fine. That's totally cool, because to be honest, it's not like they've been giving us a lot to work with on the emotions front, after all.

Until now.

The other day, during a Costanzian effort to appear busy by shuffling some science papers on deep-sea corals, I came across one that described what is apparently a relationship between a species of brittle star and a species of deep-sea coral. I was intrigued, because very little is known about such relationships. "Hold my calls" I said to nobody in particular, and dug into the text. What I would find was a story of apparently unerring fidelity in the deep, a tale of little lives lived intertwined far beyond our view. It would change not only the course of the 3:00-4:00 time slot of my afternoon, but would also give me a deeper appreciation for how complex, finely-honed, and yes, how brittle, life can be in the deep sea. Read on to be similarly touched by the affinity of an echinoderm for a particular coral, friends.

So there's this species of brittle star. Its scientific name is Ophiocreas oedipus, which translates into...something sinister, most likely. It's found in the Pacific and the Atlantic, and a few years ago, during a study of seamounts in the western North Atlantic, some scientists noticed that this brittle star species was only found along with a particular species of coral (the badassly-named Metallogorgia melanotrichos).

How tight is the relationship? Well, a total of 45 M. melanotrichos specimens were collected across 11 seamounts - and each coral hosted exactly one individual O. oedipus. No other brittle star species were found on this species of coral. And in the dive video, O. oedipus was not seen anywhere else but on corals.

And that's just the start of this particular story. The authors also found that the growth stage of the coral corresponded to the size of the brittle star - young corals hosted the smallest brittle stars, and as the corals increased in age, so too did the size of the brittle star clinging to it. Little brittle stars clung to the stalk of the young corals, whereas older and larger brittle stars were found intertwined among the branching crown of the mature corals.

This relationship starts young. The authors report that one very small (11 cm long) coral specimen collected at a later date harbored a tiny, tiny O. oedipus - one with a central disk only 1.5 mm wide. And this relationship lasts until, and beyond, death: one O. oedipus was noted on a coral of 'poor health', and an adult O. oedipus was noted on a coral that was 'clearly dead'.

So, if you're keeping track at home, these brittle stars were found only on these corals, and these corals harbored no other life. The brittle star apparently finds and settles upon the coral when both are very young, and they mature together, up to and beyond the death of the coral. 

The authors - Celeste V. Mosher and Les Watling, who were both at the University of Maine at the time - summarize the relationship thusly: 

"Evidence suggests that a young brittle star settles directly on a young octocoral and the 2 species then grow, mature, and senesce together."  

Now you're going to have to excuse me...I think that I have some dust in my eye or something.