The "starfish walking back to the sea" FAQ & why it is sad

So, apparently back in 2012, the original producer of this video shot this lone sea star out on a South Carolina beach as it was struggling to get back to the ocean, likely due to a mass stranding or some other event which stranded it on the tropical Atlantic beach..

Here's the original, very static heavy video: https://www.youtube.com/watch?v=tV5H1qNwFKo

and here is the "cleaned up" version which was released in October 2017...

This video went viral and was circulated widely in a huge number of widely read newspapers all over the world including The Sun, the UK's Daily Mail and oddly enough, the Indian Express! 

These and other venues reported it with such inaccurate hyperbole as "Incredible moment starfish WALKS down the beach after getting stranded on the sand!!" with the word "INCREDIBLE" being dropped as if this was somehow aliens landing on the Earth for the first time!


But sadly, what was happening here wasn't really THAT momentous and in fact was pretty sad.

There was no information on what was happening, what species this was or the context of this whole thing...  So here's my attempt to shed some light on this..

1. What species is this? And how does it live normally? 

This is a starfish called Luidia clathrata and these are members of a group of "sand stars" called the Luidiidae. A family with only one genus, Luidia named for a 18th century Welsh naturalist  named Edward Lhuyd whose Latin handle (they all had one!) was Luidius. One of his colleagues named this genus of sea stars after him in 1840 a story was born!

You can read lots about Luidia in a blog I wrote here in 2014!

Long story short..they eat snails, clams and other small critters in the sand. They can bury themselves in the top part of the sediment where they live.

This species in the waters of the tropical Atlantic on the US coast.. Florida, South Carolina, etc. are commonly encountered and commonly seen on beaches..

2. Seen on BEACHES? Why is THAT??
 How did this individual end up on the beach? Likely due to a mass stranding following a storm, which I've written about here... But here's a video of such an occurrence featuring many, MANY of this species stranded along the shoreline

3. What makes them so vulnerable? 
Basically these sea stars don't have a lot of "hold" on the surface because their tube feet are pointed rather than suckered. Their little tube feet are modified to help them efficiently dig into the sand or other sediment both to help them feed and to hide them from potential predators..

BUT when big waves or currents come along.. they can be swept away and taken to hostile environs such as this seashore..

Bear in mind that this species is quite abundant and while its unclear what these "natural disasters" mean for the population of these animals, I wouldn't be surprised if the recovery was relatively quick given how many of them there are..

4. What do they look like alive and "normal"???
Here is a healthy individual of this species moving naturally underwater, albeit near the beachfrot

Starfish from paul zoeller on Vimeo.

As the video would indicate..these are actually elegant and very beautiful animals in their natural habitat. In fact, Luidia is one of the FASTEST known sea star species..

5. Why is it sad?
    So, its literally been months since the original "crawling" video posted but I STILL have this being sent to me with comments about "HOW WONDERFUL IS NATURE OCEAN" or "AMAZING OCEAN CREATURE" etc. etc... when in truth this video exploits this animal desperately trying to get back to the ocean

    There's an important consideration here: Sea stars operate using a unique series of tubes in their body called the water vascular system which operates primarily using hydraulic pressure throughout the arms and so forth. This is how they move and operate all of their tube feet and so on...

via http://www.deepseanews.com/2012/03/veins-of-water-the-evolution-of-the-echinoderm-water-vascular-system/

  The water vascular system NEEDS SEAWATER TO OPERATE.

Many echinoderms DO have a limited ability to tolerate BRIEF periods out of water..but this is essentially the animal with residual water remaining in its Water Vascular System, such as the tube feet and so on..

Fluid is still required for movement AND survival. Water carries oxygen and other necessities, such as food and etc. throughout the body. 

So, that long crawl back? is not both a crawl to return to comfort but also a return for SURVIVAL.

Folks who express the "WONDER" over that pic are perhaps extending a... misplaced emotion.. 

Fortunately the original producers of the video have said repeatedly that they had returned that specimen to the ocean shortly after they shot it. So, good on them. I thank you on behalf of the starfishes!!

So, in the meantime..can we PLEASE let the video go  and LOSE  all of the sad, misplaced hyperbole about how amazing this is?? Its just painful to watch. 

thanks. 

Echinoderm Tube Feet Don't Suck! They Stick!

Image taken by Barry Fackler

A few months ago, I wrote a post that summarized ongoing developments showing how the tube feet in echinoderms (best seen in sea stars and sea urchins) was primarily based on a 2-part glue/adhesive system.

Do tube feet actually use suction as has been historically thought/taught??

The whole "tube feet use suction" paradigm is a powerful one that has been observed since some of the earliest work on starfish in the 1840s. 

Its a powerful and seemingly straightforward idea. Tube feet have what appears to be a suction cup on the tip of their tube feet, and so, therefore, shouldn't it work like one??

Could this long-standing notion... BE WRONG???

Image by "ratexla"/Josefine Stenudo

The suction cup idea is pervasive and can be seen in many pop culture references.

How pervasive?  The authors of the paper I use below cite Peach the sea star from the recent movie Finding Nemo by Pixar- Peach uses the popping sounds that one associates with a rubber sucker!!

A new, recent paper from the bioadhesion labs of Patrick Flammang in Belgium, and Romana Santos and Elise Hennebert in Portugal have demonstrated several experiments that in fact, tube feet rely on adhesion (as outlined here before) and NOT on suction. This paper is OPEN ACCESS and can be found here at the Proceedings of the 7th European Echinoderm Conference! 

The paper is important to people who study echinoderms but is very straightforward and pretty easy to understand...  The authors work primarily on two species as test subjects:  

The common N. Atlantic sea star Asterias rubens

Image by Juncea

and the European urchin Paracentrotus lividus...

Photo by Marco Cortesi

Even before this recent work on adhesion in tube feet, there had been indicators, some years ago that suction was not the only force in tube feet at play. Why?

First-A study from 1985 (Thomas & Hermans) showed that echinoderms have been observed adhering to screens, meshes and grates-so how would a suction cup work if they were being applied on a porous surface with no way to create a vaccum?

Second.Tube feet leave footprints such as this one which leave behind residue suggesting a glue or adhesive was at play..

In order to test whether suction played an active role in adhesion (in other words they attempted to DISPROVE the role of suction), the authors approached the problem with some very insightful observations/ experiments.

1. Observing the tube feet directly!

The physics of your basic suction cup model is pretty straightforward. The suction cup creates a large suction cavity between the attached foot and the substrate (i.e., the ground).  

When you put a suction cup down, you press the top down and pull it up. This creates the suction cavity that attaches the suction cup to the ground..that's what you would expect.

Tube feet from Asterias (the starfish) and Paracentrotus (the urchin) were sampled immediately after it was clear they were attached, and photographed with a Scanning Electron Microscope. Histological (i.e. tissue) sections were also taken...

The top two pics (A+B) show an unattached tube foot.. But C through F? all show those attached to the bottom.

Figure  1 from Hennebert, Santos and Flammang, 2012

What they found? There was NO "suction cavity" between the tube foot edge and the substrate (i.e. the ground). The tube foot disc surface was actually flat and flush with the substrate surface. Thus, no physical evidence for suction could be observed.
The authors indicate that suction may still play a secondary role, serving in conjunction with the adhesion/glue but for the most part it doesn't look like suction is a primary influence here.

2. Measuring the Attachment Strength of the tube feet

Next, Hennebert and her coauthors measured the attachment strength of the tube feet relative to different variables. These included

A. Measuring the strength or tenacity (in terms of Force or Tenacity) of sea urchins as they hung from a glass plate at different angles.
They tested the adhesion of the tube feet on glass relative to detachment force (how hard they pulled) and pulling angle (the direction). That is they tried to pull it off and at different angles on a smooth glass surface.

fr. Fig. 3A in Hennebert et al. 2013

If this were truly suction then the tube feet would slide (i.e., no resistance) and the amount of suction would decrease. There was no (or at least no statistical) relationship between the detachment force and the pulling angle.

B. Measure strength and tenacity on a porous bottom

This one was more straightforward-if tube feet are anchored by suction, then an imperfect bottom (i.e. substrate) won't really work well as a good anchoring ground. 

The authors used a sheet of plastic with holes present in the surface.  They measured tube feet with a device that measure the force and tenacity and then recorded the footprints based on whether they completely, partially or did not cover the holes.  

Prediction:  If the tube feet use suction-the force measurements for strength and tenacity would be significantly affected. But if adhesion was at play, then the holes should make no difference.

Basically, this experiment mirrors the early observations of watching starfish or urchins moving around on a metal grate or mesh. How important can suction be if the animal can move on a non-porous surface?

 No statistical differences were found between the different groups (i.e., the tube feet that walked over a complete, partial or covered hole). 

CONCLUSION!  And so, not only has prior work (see earlier blog post) shown the huge role of adhesion/glue in the way tube feet work but now, the original historical model..i.e., tube feet use suction has been pretty effectively undermined if not disproven outright!
Its possible of course that there are further refinements to how all of this works in sea cucumbers and crinoids but starfish and sea urchins have always been the "model organism" for studying tube feet in echinoderms. 

One of the oldest and most widely known perceptions about echinoderms? Not the case. Evidence is slowly building up against it and an important lesson in science that even the most long-standing ideas can be overturned when you look at the facts with the right questions!

Starfish Leave footprints! aka How Starfish Tube Feet Work! (21st Century version)

Image by veronica07

I betcha you guys didn't know that starfish left FOOTPRINTS did ya??  I don't just mean impressions on the sand..I mean, put a starfish on a smooth surface, like glass or rock and it leaves you one of these...

WHAT??  How does THAT work?

Hasn't the model always been that starfish tube feet work like suction cups (such as here) ????  Why would they leave footprints on a smooth surface if they work like suction cups??


Image by Symbiotics

THAT is a good question.

To answer it, I consulted the works of Patrick Flammang and his research lab at the University of Mons in Belgium. One of many papers addressing the biology of tube feet is utilized here (written by Elise Hennebert and others in Flammang's lab)

So, it turns out that the whole tube foot adhesion process is a LOT more complicated than the whole "its a suction cup" explanation that used to be offered in text books.

It turns out that the whole chemistry and physical processes of tube foot adhesion is actually quite complex and has very useful applications in adhesives, glues and so forth.

There is an important lesson to be learned here. This field of study started largely as an academic pursuit, to learn about the mechanisms used by these animals to survive in their habitat but may soon lead to something with many practical applications..

See this article awhile back about how Gecko adhesion has led to new types of adhesives! Adhesives that work under water would presumably have a multitude of uses..

How does this whole tube foot adhesion/stick to the ground thing work??   Here's a breakdown of the process as taken from Hennebert et al. (2008) in the Journal of Structural Biology...

1.Contact! The process begins with the contact of the tube foot with the ground/substratum.

There is a special layer called the "fuzzy coat" (shown below in red) which is present on the surface of the disk epidermis making contact with the bottom. 

Echinoblog Art Dept.- Note that "Smuck" is not known to be a true starfish tube foot noise!

2. "Film" Upon contact two different kinds of special "adhesive cells" release substances onto the  substrate (aka the ground) which form an even film (shown in green below). 

Echinoblog Art Dept. Did you know that ! can be used to make everything more exciting?!!

3. "Mesh" At this point one of the adhesive cells releases a substance that starts to form a thick "meshwork structure" (shown below in yellow) in the fuzzy coat. The mesh expands and "bulks up" creating more structure within the fuzzy coat.

Echinoblog Art Dept. Coloring is fun!

Here is an SEM of what this looks like...

fig. 1B from Hennebert et al. 2008

 4. Detachment.  When the tube foot releases, a THIRD substance-a "de-attaching" substance is released from the disk epidermis. This is something that permits the tube feet to detach easily and at the animal's will.

This leaves the "fluffy layer" and the "bulked" material behind...

Here is an SEM of what this looks like after the tube feet have been pulled away

Figure 2C from Hennebert et al. 

5. Footprint And the wet parts of the "fluffy layer" dry out leaving the "bulked" material aka the starfish (or whatever) footprint..

Here is what that part which is left behind looks like in 3D via Transmission and Atomic Force Microscopy

Fig. 3 from Hennebert et al.

And here is an image of the tube foot "foot print" as seen directly off a piece of glass..

And so...
What about that classic paradigm about suckers on sea stars and other echinoderm tube feet basically being suction cups???

Well, nothing definitive has been published as yet..but Flammang's lab has published on these adhesive processes in tube feet for over 10 years. A title from an oral presentation at one of the last European echinoderm conferences by Elise Hennebert, Romana Santos and Patrick Flammang here, entitled "Echinoderms don't suck" does seem to imply the days of that mechanism are numbered.

Bear in mind that this doesn't even necessarily end with this one tube foot type. There are at least two other forms of tube feet and exploring the various mechanisms at play could be fruitful indeed...

In addition to the lab run by Patrick Flammang at the University of Mons, this lab in the UK (shown in this video) has also undertaken research into this area to understand the nature of tube foot adhesives...

UPDATE:  To see the follow up to this story and to see how "echinoderms don't suck" go here!

Holding on in a Rough World: Colobocentrotus atratus-the Shingle Urchin!!

Today's we shift gears from starfish and take a look at sea urchins! Today we look at Colobocentrotus atratus (Echinometridae), a commonly encountered resident of the South and Central Pacific rocky intertidal. If you've ever been to Hawaii they can be frequently encountered along the edge of the harsh-wave swept habitats along its beautiful volcanic shores.
They are commonly known as the Shingle or Helmet Urchin and in Hawaiian is known as kaupali which translates to "cliff-clinging"... (thanks to John Hoover's Hawaii's Sea Creatures for this info)
Notice the uniquely flattened shingle-like mosaic of modified plates covering the surface as well as the flange of flattened spines forming a close fringe around the edge.

Colobocentrotus lives in heavy wave-swept environments and its smooth, flattened plates lead one to automatically interpret them to be adaptations for surviving in these kind of environments.

A recent paper by Santos & Flammang (2007) investigates the biomechanics of how these neat beasties hold on.

It turns out..its ALL in the TUBE FEET!



They measured the adhesion of this species against other more "normal" sea urchins (e.g., the spiny Echinometra) and they found that Colobocentrotus always presented the highest measured values.

* Colobocentrotus' attachment force allowed it to resist dislodgment up to water velocities of 17.5 m/s and even up to 27.5 m/s!!! In contrast, more "typical" echinoids, like Echinometra were disodged by water velocities superior to 7.5 m/s.

How fast is 27.5 m/s??

.....basically if this was compared with a strong windy gale..that would be enough to uproot trees and cause minor damage to buildings!!! Holy Carp!! (and according to Patrick, given the density of seawater, wave strength would actually make it WORSE!)

* The shape does not appear to affect the difference in drag and lift but may function to offset the amount of shear force directed onto the animal into normal force..effectively spreading the energy load around more evenly on all tube feet.

Thus, it seems that the ability to inhabit extreme water velocities in Colobocentrotus is tied to its very high number of tube feet and not to its particular morphology (although it does seem to help in other ways).

Adaptive notions for the overall shape suggest several ideas, including:

1. The streamlined morphology might be an adaptation to lessen other hydrodynamic forces such as wave impact.

2. The flattened spines may reduce spine breakage and therefore the energy expense of constant repair, etc.

3. The morphology seems ideal for retaining extra water which can be essential to resist heat and dessication stress at low tide.

This latter idea seems interesting given this pic of Colobocentrotus huddled together....


Tough little wee beasties...so for goodness sakes! leave em' alone when you go out tide pooling!

(Photos courtesy of Flickr and Photobucket!)