Wednesday, April 22, 2009

More on Feather Stars!! How Long Do They Stick Around?

So, we are doing feather stars these week! While researching the post earlier this week I stumbled upon an interesting concept. How long do crinoids stay in the same place???
(from C. Messing's Crinoid site-damn, he has good stuff there-you should go take a look at it!)

You can often see huge bunches of crinoids sitting on rocks or coral or some other kind of perch.

They sit and taking advantage of water currents as they flow by... Often there are many. Sort of like if you have good cell phone reception.....

But did you know that crinoids actually have what's called "site fidelity"? That means that they will remain on a single perch for a long time!

So how long?
(Stephanometra sp. from the SE museum site)

The material for this post is largely derived from a paper by Nerida Wilson (2005, Coral Reefs 24: 99-101)-currently at Scripps, working with Greg Rouse which focused on crinoids in the family Mariametridae, primarily Stephanometra, Lamprometra and Liparometra.

(Liparometera sp. from the SE museum site)

It turns out that crinoids will stay in the same place for A LONG TIME (although some may not come out until the sun goes down).
  • Some are known to stay in the same place for up to TWO years!!!
  • One account actually reported a crinoid that stayed in the same "residence" for FIVE years!!
  • Some observations series have continued for over SIX MONTHS with no apparent change!

Wilson observed 13 mariametrid crinoids on a total of 11 perches. There were some individuals that "left" and returned but on the whole...

She observed over the 59 day period that 80% of the crinoids continued to occupy their original perches!

Big feeding clusters like this one have interesting dynamics. Its thought that these big bunches may improve feeding efficiency by slowing down water currents. Big individuals tend to be solitary whereas a bunch of smaller ones will aggregate.

But apparently, there IS competition among individuals for a specific perch with a "winner" forcing the "loser" from the most ideal perch.

So, what have we learned? Crinoids apparently stay in a SINGLE place and they will work to stay there.

Who'd a thot something so innocuous what have so much depth?


Jan-Maarten said...

This is so fascinating! How does a crinoid recognize a 'good perch'? What rules the little beasty does follow in moving towards such a place?

Alex said...

It's all about water currents for them. They likely sense currents using their tube feet, though I don't know that anyone has a definitive answer for that. Probably looking at how other echinoderms detect their environment would be a good place to start.

ChrisM said...

What would dictate a 'good perch'? I presume that would be water current flow and feeding dynamics...They hold their arms into the water and pick food out of the a good spot would be highly sought after.

but beyond that? only they know for sure...:-)

Peter Etnoyer said...

They could be self-sensing, if a good perch is defined as somewhere crinoids have been before. This is demonstrated before, I forget whether it was corals or urchins or both. Gotta look that one up.

YoUsed2beCool said...

How exactly do crinoids go about moving themselves from one perch to another? Do they release their foot or some sort, and just float away?

Alex said...

They crawl, primarily by using their arms. This occurs frequently in feather stars, but also in sea lilies:

Feather stars also swim, but not to get to point A to point B, but rather to escape tough spots.