Showing posts with label urchin. Show all posts
Showing posts with label urchin. Show all posts

Tuesday, February 4, 2014

What we know about the world's most venomous sea urchin Toxopneustes fits in this blog post!


Toxopneustes! aka the "Flower Urchin" is one of four species of Toxopneustes (all of which occur throughout the tropical Pacific). One species, Toxopneustes pileolus is one of the most frequently encountered and as such, this is the name most often applied to sea urchins that have the distinct appearance (as seen above).

Toxopneustes literally means "toxic foot"undoubtedly alluding to the MANY venomous pedicellariae that compose the animal's appearance. I'll explain "pedicellariae" more below..but just so you know what I'm talking about? ALL of those yellow circles and traingles in the picture above? Those are tiny little claws and each one of them is toxic. So be careful around these guys..

Toxopneustes has all of the other stuff that you see in other sea urchins, such as spines and tube feet.

The circles and triangles below are pedicellariae. Round means the pedicellariae are "open" and the triangular ones indicate the pedicellariae are either closed or are closig.  The brown rods below that kind of look like toothpicks? Those are the spines, which are actually not themselves toxic (as far as I've read).


Toxopneustes has been known for quite a long time. The genus was described in 1841 by Louis Agassiz, so we've had some time to think about it.

This then, is the puzzle. Why do we seemingly know so little about it?? As we'll see, it has a formidable reputation as a highly venomous species and its a prominent tropical sea urchin but really, a lot of what we know essentially boils down to this....

1. Toxopneustes pileolus displays covering behavior. 
I have discussed and blogged about "covering behavior" in the past (here). Toxopneustes is a "collector" urchin, which means that it shows the curious behavior of adding rocks and other debris using tube feet and/or pedicellariae to cover over itself.

Although the reasons are not well understood, it is thought that this could serve to protect the urchins from ultraviolet rays. In some cases with other urchins, its thought that the materials serve as defense, but given the highly venomous pedicellariae on this species, I kinda doubt that's the case here.

One paper, which studied the East Pacific species, T. roseus (here) suggested that the covering response protected the animals against wave surge while they fed on coralline algae in rhodolith beds. 


2. Flower urchins spawn in the Spring and "undress" their covering materials to do it! 
This one is self-evident since all animals have to reproduce. And most echnoderms spawn externally. But it was only recently in a paper by Andy Chen and Keryea Soong in Zoological Studies in 2009 which showed that they showed Toxopneustes pileolus "release" all of the materials obtained via their "covering response" before they spawn.

Here is Figure 1 from Chen & Soong 2009. Showing on the left, a "covered" urchin and then on the right an urchin "uncovered" and spawning.

3. They hold the distinction of "World's most venomous" sea urchins 
     Here we have the #1 feature, this sea urchin is known for: its sting! One species in particular, T. pileolus is regarded by the 2014 Guinness Book of World Records as the "most toxic" of sea urchins (see lower left corner).

The poison is served via the pedicellariae which are all of those triangular and circular structures that you see on the surface of the urchin.. Here the pedicellariae are all agitated. How can you tell? Note that they are all triangular instead of round. That means they are closed and have been recently agitated...


Here is more of a closeup of each one. Each with a stalk connecting them to the body. They are round when open and more triangular when closed.
                   
Here's a diagram of one, showing the hard parts within all of the softer covering. Basically, each one is a claw that injects poison.
                                            
And below is a nice SEM image of a similar kind of pedicellariae from the East Pacific species. Toxopneustes roseus showing it in  more detail.
From the Echinoderms of Panama Lifedesk by Simon Coppard
4. How Toxic are they?? 
From this Japanese blog. Do not do this. It will hurt (I mean the pedicellariae. Going to the blog shouldn't hurt). 
Well, strangely enough, there are very few modern (read-quantiative) accounts of how toxic/painful/ potent Toxopneustes poison can be. However, I did locate an older account from 1935 by Dr. Tsutomu Fujiwara at the Hiroshima Zoological Laboratory in Japan who reported his experience with being stung by one (italics and paragraph break are mine) in Annotationes Zoolgicae Japonenses 15(1): 62-68 
     On June 26, 1930, while I was working on a fishing boat on the coast of Tsuta-jima in Saganoseki, I scooped up with my bare hand an individual of the sea-urchin which had been carried up by a diver with a fishing implement on the water surface from the sea-bottom about 20 fathoms in depth, and I transferred the sea-urchin into a small tank in the boat. At that time, 7 or 8 pedicellariae stubbornly attached themselves to a side of the middle finger of my right hand, detached from the stalk and remained on the skin of my finger.
     Instantly, I felt a severe pain resembling that caused by the cnidoblast of Coelenterata, and I felt as if the toxin were beginning to move rapidly to the blood vessel from the stung area towards my heart. After a while, I experienced a faint giddiness, difficulty of respiration, paralysis of the lips, tongue and eyelids, relaxation of muscles in the limbs, was hardly able to speak or control my facial expression, and felt almost as if I were going to die.  About 15 minutes afterwards, I felt that pains gradually diminish and after about an hour they disappeared completely.  But the facial paralysis like that caused by cocainization continued for about six hours. 
Other accounts have detailed stopping oyster hearts, and contraction of smooth muscle, including cardiac (heart) tissue. Some accounts of Toxopneustes have stated that swimmers have drowned following stings but I wasn't able to verify an account of this.

Is it any worse than the venom in other poisonous urchins, such as these echinothuriid "fire urchins"??? 

5. What we DIDN'T know about commensal crabs (but do now, thanks to the internet!)
That's a bit of a cheat. We DID know that commensal crabs live on Toxopneustes.  Apparently, these striped little fellows are called Zebrida adamsii. The name "Zebrida" undoubtedly hailing from the zebra-like stripes on the animals' body.

Here's one living on Toxopneustes pileolus with some eggs! 


But what is REALLY interesting is just HOW these crabs live on the urchins! Look at the video below.
They actually CLEAR off the pedicellariae and spines and live on a bare patch of the animal surrounded by all the poisonous pedicellariae and etc. 


Questions!? 
How far/how long do they hitch a ride?
Do they feed on the tissue from the tube feet and pedicellariae?
Are those "bare patches" long term? Or are they only from acute attacks? (those crabs seem to be pretty comfortable there!)
Are the crabs as well camoflaged as they seem?
Interestingly, note also that the pedicellariae are all open and seemingly comfortable. Does that mean they are pretty cool with the crabs living on them that way?  What do the urchins get out of it?
IS Toxopneustes REALLY the world's most venomous sea urchin???

Someone go find out and tell em' the Echinoblog sent ya! (unless you get stung-then uh.. it wasn't)

Tuesday, July 30, 2013

The Gorgeous Sea Urchin Skeleton: An SEM Odyssey

Sea Shell
Image by gary.brake
The Scanning Electron Microscope (SEM) is a wonderous device. Simply put, electron beams provide a highly detailed almost surreal image of the surface they are directed at.

But what happens we direct an SEM at animals that are ALREADY kind of weird? The striking beauty of sea urchins is revelaed!

The sea urchin skeleton. Also known as a TEST.  One of my many regularly repeated caveats- these are NOT shells. These are underlying skeletons which have a layer of skin which is typically removed to reveal the more aesthetic skeleton...

Here is an example from a cidaroid sea urchin.. Those round knobs or bosses?  Those are where the spines articulate with the body...
Cidaris 1
Image by Gripspix
Here's a nice macro shot of aforementioned "boss" (=the knob which connects with the spine).
test photos
Image by "Nervous System"
But what happens when we focus a Scanning Electron Microscope (SEM) on these surfaces?  (note that these images are a different species from the one above).
sea urchin
Image by Monkey.grip
Here's another view looking down. Note how the skeleton is actually porous! Echinoderm skeletons aren't simply inorganic calcium carbonate, they are actually infused with tissue...
Sea Shell
Image by gary.brake
sea urchin
Image by Studio Jonas Coersmeier
Another view from a different perspective...
Shell-7
Image by particlesixtyfour
sea urchin landscape
Image by monkey.grip
Closer...
Shell-2
Image by particlesixtyfour
..and closer still!
Shell-4
Image by particlesixtyfour
right on top of it!
Shell-18
Image by particlesixtyfour

But wait! What about the SPINES???   I'm not sure which species these are from.. but they give you a good idea about the fine topology that one might not realize is present from simply looking at a spine with your eye... 
Spike-1
Image by particlesixtyfour
Closer!
Spike-2
Image by particlesixtyfour
And finally... CLOSEST!!
Spike-3
Image by particlesixtyfour
And just to cap off the whole odyssey through a sea urchin spine... here is a cross section THROUGH a spine magnified 150X!!!   The final three images below are from the Biology Dept. at the University of Dayton! 
Here are the featured spines...
 and together to show perspective...

Tuesday, July 16, 2013

URCHIN BARRENS! Aka the Trouble with Tribbles (=sea urchins!) Post!

Purple Urchins
Image by Annie Crawley
Sea urchins are among the best known, most heavily published on, and most "important" of echinoderms. People eat them and they are studied in marine ecology pretty heavily. Most marine biologists I know think highly of sea urchins. They're pleasant animals with an unusual appearance

But the truth is, no matter how adorable or fuzzy, useful and/or cute an animal may be, TOO many of them is nothing but trouble! True for Star Trek tribbles and for sea urchins!
(disclaimer: Tribbles are science fiction, sea urchins are not)

*Tribble factoid: Someone has ACTUALLY given tribbles a scientific name: Polygeminus grex! don't believe me? go see Memory Alpha!)

Tribbles are actually a GREAT introduction for today's topic: SEA URCHIN BARRENS!

What are Sea Urchin Barrens??  These are places where a sea urchin species' abundance increases dramatically to the point where the urchin devours EVERYTHING in its path, effectively leaving all else 'barren' except for more hungry sea urchins.
Purple Urchins
Image by Annie Crawley
DSC_001720091004
DSC_003020091004
Images above by AndyOlsson
This is not far removed from the imagined "ecology" of Star Trek's tribbles (A good essay applying real population math about tribble populations can be found here, but this image from the famous ST:TOS episode hopefully gives you the general idea!)
Image from TrekNews.net
The gist of it is simple:  TOO MANY URCHINS and they EAT TOO MUCH. But unlike tribbles (which were eradicated by Klingons-yes I know they're not real), in the case of sea urchins, we can actively study the ecological interactions and conditions which have caused the populations to explode in number.
DSC_001720091004
Image by AndyOlsson
Here is a video showing tons and tons of Red Urchins (S. franciscanus) on a barren in Southern California. Thee bottom is essentially devoid of all but more hungry urchins!



What causes urchin barrens? 
Um. Its complicated but the common thread seems to be that there is an association between barrens and the absence of sea urchin predators.

In many of the papers I've read about Northern Hemisphere species, the loss of a major sea urchin predator seems to be one of the immediate attributed causes of the runaway population growth, but as we've seen with other species such as the Crown of Thorns (Acanthaster planci) the story is often complicated....

Most of the studies involve temperate-cold water urchins in the Strongylocentrotidae, specifically Strongylocentrotus purpuratus (purple urchin), S. franciscanus (red urchin), S. droebachiensis (green urchin) and S. polyacanthus.  Literature was abundant, but this paper by Nathan Stewart & Brenda Konar provided much of (but not all) the info for this post.

In one of the most familiar studies from the Pacific Northwest coast, the main predators were sea otters (in many cases, I assume Enhydra lutris-some papers did not mention species).

The fundamental ideas outline the notion that as sea otter populations decline, predation pressure decreases and with nothing to keep the populations at a controlled level sea urchin populations dramatically increase and began to devour kelp (and really everything else!)  to the extent that they effectively clear the bottom.
Urchin Barren
Image by Santa Monica Bay Restoration Foundation
Purple Urchins
Image by Annie Crawley
In Stewart & Konar's paper, individuals from these population explosion urchins were compared against "healthy" urchins which occurred naturally in kelp forest habitats.  Some dynamics:
  • Urchin densities were SEVEN times greater than those elsewhere
  • Kelp forest (vs. 'barren') urchins were larger and more robust
  • "Barren' urchins were smaller with less tissue
  • "Barren urchins had little to no reproductive tissue compared to kelp forest urchins
Different species of Strongylocentrotus (as well as other urchin species!) live in different places and have different predators!

On the North Atlantic coast, there is a similar population explosion of the Green Urchin, Strongylocentrotus droebachiensis, which from the look of it, is pretty severe

Here's a video that shows just WOW... a lot of them..

I have briefly written about the impact of this many Green Sea Urchins. They all POOP! This actually has a pretty serious ecological impact. 

Some, such as this paper, have proposed that these population increases have been caused by the loss of lobsters (Homarus americanus) which feed on green sea urchins. But in all liklihood, as the system is better understood the more complicated the explanation.
Northern Lobster, Gulf of Maine
Image by AJmart
Other predators, such as wolf eels and starfish, also feed on green sea urchins and well.. it can get messier...

Now, in the Southern Hemisphere we have a similar, parallel situation with a completely different family and species of sea urchin: Centrostephanus rodgersii (Diadematidae).
Sea Life: Long Spined Sea Urchin
Image byEdward Vella
Climate Change Enters the Picture! 
A paper by Ling et al. 2009, in the distinguished Proceedings of the National Academy details  a scenario with some important dynamics
  1. The range of the urchin is dramatically expanded because of increasingly warm waters in/around the eastern Tasmanian region.
  2. The lobster Jasus edwardsii is one of the primary predators of Centrostephanus and has been heavily overfished. The BIG lobsters that would feed on urchins are taken for food leaving the urchins to run amok!
Its important to note how significant the human factor has played into these dynamics. Climate change and overfishing are thought to be the primary agents responsible for urchin "barrens" in these circumstances.

This issue has been conveniently summarized in this video...


The takeaway lesson: Predator loss seems pretty strongly associated with urchin "barrens" aka population explosions. But all sorts of environmental factors, including warmer waters, and multiple predator interactions can be important..

So we have a LOT of sea urchins. Couldn't we uh..just eat them? 

Yes. 

BUT, you can after all, only fish so much. After you've taken the lobsters, the urchins and the kelp what else have you got left? A good answer seems to lie with good sustainable fisheries management..but we shall see how this works out...

Tuesday, January 29, 2013

Echinoderm Tube Feet Don't Suck! They Stick!

Side B
Image taken by Barry Fackler

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???
20040128_4 Podia of starfish, Asterias rubens (Sweden)
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
Common Starfish,Filey Brigg,North Yorkshire.
Image by Juncea
and the European urchin Paracentrotus lividus...
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!

Wednesday, July 9, 2008