Tuesday, September 28, 2010

Stichaster australis-A Pisaster-like parallel species!!

This week's blog is a strange collision of starfish and comic-book/science fiction geekery!

So, one of my favorite sci-fi notions is that of the multiverse or parallel earth-essentially that you can have a universe that is JUST LIKE the one you live in but differs in minor to substantial ways.

So, for example, one of my favorite graphic novels by famous comic book writer Grant Morrison
Which is basically about DC's famous Justice League (Superman, Batman, Wonder Woman) meeting their evil parallel counterparts!!

Batman vs. Owlman! Superman vs. Ultraman! Wonder Woman vs. Power Woman! As the image above suggests, each are parallel versions of each other!

Each is a parallel version of the respective character. In other words, you kinda recognize the ROLE of the character but the character itself is fundamentally different and seems out of place, compared to what you are familiar with...

And I realized..this is kind of a cool way to think about the parallel niches that you can see in starfish that live a WHOLE world away from one another. VERY similar. But VERY different!


So, let's take the example of the New Zealand Stichaster australis...

Stichaster australis
is a shallw-water species that occurs along the rocky intertidal throughout the temperate regions in New Zealand.

Their main food is the abundant New Zealand green mussel, Perna canaliculus.

Apparently, S. australis is one of the mussel's primary predators in the rocky intertidal! Hmmm...where have we heard that before??

A 1971 paper (click here to see ref) that was studying the ecology of Stichaster australis by the famous ecologist R.T. Paine showed that this was similar to the North Pacific Pisaster ochraceus, in that S. australis played an important role in regulating mussel populations!
Paine experimentally removed S. australis from a rocky intertidal region for 9 months, resulting in the mussel expanding its vertical distribution by 40% of the space it had to grow into!!

Species richness of the area where Perna had "overgrown" decreased from 20 to 14 species

And when they removed Stichaster in conjunction with the other dominant organism-the kelp Durvillea antarctica, they found that the mussels had occupied 68 to 78% of the available space in the area!!

So, without the "control", of the predator or the space occupied by the kelp, the mussels would just spread out into the area and go as FAR as they could take it.

Okay.. So what?
I've mentioned the ecological role of the North Pacific Pisaster ochraceus as the typical example of what's called a keystone species aka a species whose presence has a "disproportionate effect on its environment"
Basically, removing Pisaster results in a similar cascade of mussels going amok! Diversity takes a nose dive, etc.

And what I've just described for Stichaster australis is pretty much the same thing! Except that they live at opposite ends of the Earth!

The intertidal habitat in New Zealand has a lot of close parallels to those in California or anywhere on the west coast of North America...

You've got mussels..except that in North America they are Mytilus spp.
and in New Zealand (Southern Hemisphere)..you instead have Perna canaliculus

In the North American system you have Macrocystis pyrifera
but in the southern hemisphere you have Durvillea antarctica

and finally, you have the asteriid Pisaster ochraceus in the Northern Hemisphere... with its distinctive intertidal skeletal morphology
And here's the stichasterid, Stichaster australis in the Southern Hemisphere.. with a curiously, SIMILAR appearance!
Here we have Stichaster in a big cluster. Various hypotheses on why they do this I've read have focused mainly on how these big cluster maximize reproduction...
...and here we have the rocky-intertidal Pisaster in a curiously similar cluster. Reasons I've heard offered why-have extended to resisting dessication...but I suppose maximizing reproduction is also possible....Thus, the ecological roles these two species appear the SAME but the players are different.

This actually extends beyond being different in a lot of cases. Several of these taxa are not even closely related!

australis is found ONLY in New Zealand and Pisaster ochraceus is found ONLY on the west coast of North America, and belong to two completely separate families!
(although admittedly, the families are related).

and yet, they have a similar convergent appearance, live in the same settting, feed on the same kind of food, and maybe even practice similar kinds of behaviors.
There are MANY more intertidal invertebrate species, including various snails and barnacles, that have similar parallels...

and course, New Zealand has MANY more starfish species intertidally-and relative to say, those in North America, their ecological roles are pretty poorly understood..

but in this instance, same role-but different players!! Not parallel earth-but parallel starfish!!

Tuesday, September 21, 2010

Videos of Sea Cucumbers doin' Sexy' Swimmin' Crawly STUFF' !

I have some good stuff coming up, but this week got away from me.. So in the meantime, here's some neat sea cucumber videos that I've been meaning to share....

A giant holothurian doin some kinda sexy thing! There is some gamete emission towards the end and is kind of understated, so keep your eyes open...

Here is a nice compilation of deep-sea marine invertebrates from off Kona, HI shot by the NOAA Okeanos Explorer... Some fantastic hi-def video of the swimming sea cucumber Paelopatides from 0:28 to 0:45 into the video.. The rest of it is mostly not echinoderms, but also interesting...

And finally, if you want to see some MORE neat deep-sea sea cucumber goodness! Go HERE for footage from the Indonesian deep-sea INDEX 2010 expedition video...

A giant synaptid sea cucumber (identified as Synapta maculata) on the move!

Not sure where this video was shot, but possibly the Indo-Pacific..

...and video of another sea cucumber feeding. You can see the tentacles moving food into the mouth.. From Lembeh Straits in Indonesia.

And of course, where would we be without watching sea cucumbers POOP!?

Monday, September 13, 2010

Pteraster & Kin- Starfish that FIGHT BACK with MUCUS!

Everybody LOVES mucus! Yes! Don't deny it!

What would our lives be without it? Dry, boring and unlubricated.

I thought I would kick off the Fall with one of my favoritest and weirdest of echinoderms.. Pteraster and its kin aka the Slime (or Mucus) Stars!!


Pteraster is one genus in the family Pterasteridae.

This is group of starfishes that includes 8 genera that mostly live in cold-water habitats, but are most diverse in the deep-sea. The genus Pteraster alone includes about 45 species that occur worldwide, from the Arctic to the Antarctic and all the deep, dark places in between... Many of them eat sponges. So, on the surface, fairly harmless..

We'll be focusing on one particularly well-studied species, Pteraster tesselatus that occurs on the west coast of North America between California and Alaska.

This is a sort of thick, pudgy looking beast that can have a diversity of color patterns...
What makes Pteraster and all of the Pterasteridae so unusual?

The surface of the animal is actually concealed below a tent-like covering [called a SUPRADORSAL MEMBRANE (SD in the figure below)] that extends OVER the animal's proper surface!!

That proper surface below the supradorsal membrane is where you would find the typical features on a sea star's surface, such as the gills and etc.. Here is a cross-section through the arm. Tube feet on the bottom.
Why is this important? Well, its through the supradorsal membrane that the SLIME comes out!!

2. The SLIME Star!!
So, let's cut to the chase-Pteraster tesselatus earns its common name "the Slime Star" owing to its ability to defensively SPEW MUCUS when annoyed by unwanted contact (and who wouldn't want to do that??) !! GOBS and GOBS of it.

Note to you grammar types... MUCUS= noun. MUCOUS=adjective!

(this photo from the Stony Brook mar bio page)

This picture illustrates a typical encounter with Pteraster. Pick it up, and the next thing you know...you've got a bucket full of mucus!

Much of the info presented herein was based on studies by James Nance (Texas A& M University) and Lee Braithwaite (Brigham Young University) from some neat papers in 1979 and 1981 in the Journal of Experimental Marine Biology & Ecology.

How It works!
Within the supradorsal membrane are a VAST number of mucus producing cells both on the surface and throughout pores present all throughout.

When Pteraster feels threatened, water enters the animal via the bottom tube foot grooves and flows throw the body cavity and up into the cavity between the animals' surface and the supradorsal membrane.

Mucus is produced by cells in the supradorsal membrane.
An opening in the supradorsal membrane, called the osculum, which is normally open

suddenly CLOSES

....and all of the little pores in the supradorsal membrane OPENS!!

So, water pressure EXPELS the Mucous-Water mixture out of the supradorsal membrane!!
So..imagine suddenly stopping up the pipes in your bathroom....and watching it all go somewhere else...
ShABLURRRUUUUUBBBBPTTTHHHHHHHH!!!!!! (noise is simulated-Pteraster does not actually make this noise unless you REALLY want it to. Then, go ahead-knock yourself out!)and you get THIS!
But WHY does it do that? Would could POSSIBLY offend such an innocuous creature? That just wants to sit around eating sponges all day?

On the west coast of North America, starfish ecology usually involves one of these two predatory "bad boys"...

Solaster..usually Solaster dawsoni, which feeds mostly on other starfish.
(One species of Solaster shown here eating a sea cucumber.. pic from the SIMON/NOAA/MBARI)

Solaster (diameter=24 cm) can apparently take up to FOUR DAYS to devour an undefended Pteraster (about 14 cm across)! And that's basically Pteraster being devoured alive!

OR the fearsome Sunflower Star..Pycnopodia helianthoides which usually just SWALLOWS their prey whole! This takes about 2 days to digest...
(photo by Allison Gong, UCSC)

Tests using mucus applied directly to food being eaten by either of these two species almost instantly resulted in the predator moving away VERY quickly.

Lab tests applying mucus to fish and other invertebrates, such as snails and etc. also results in avoidance or outright fatality following extended exposure.

The mucus probably contains saponins or something similar. I've talked about how 0ther starfish species use saponins as a means of discouraging predators here..

What about other Pterasterids?
So, I've mentioned other deep-sea starfish related to Pteraster..such as this Hymenaster from
the deep sea North Pacific, which is practically MADE from clear gelatinous goo!
...and here...(about a foot across)
And if you pick them up? You get the mucous love!
or to say it another way.. "It slimed me!"

But this simple behavior begs a lot of interesting questions.
If the slime is defensive then WHAT PREYS on the other species around the world in the deep sea?
What about the tropical Pacific Euretaster?
Is the slime more or less toxic where specific predators are around?
How has this affected the long term evolution of the Pterasterids?

All questions for another day. Pteraster is interesting for MANY reasons that I haven't even begun to address...

Tuesday, September 7, 2010

Echinoblog Sneak Peek of the Hyperbolic Crochet Reef!

One of the great things about being "the starfish guy" is that people come to you with starfish questions that they don't think anyone else can answer. For the last two weeks, I've been getting some really NEW kinds of questions!

"Can you Identify this?"

Not a hard question... I do this for a living, after all... But then they dropped THIS in front of me!
A crocheted tropical reef starfish!

What could it be?? And why was it made?

It turns out that in October, the NMNH will be hosting a satellite "reef" of the Hyperbolic Crochet Coral Reef Project!!!

I have demonstrated my love of knit and crocheted echinoderms before (go here to see)! And am looking forward to seeing this! Especially since I'm seeing what kinds of things are going into it.

Here is the NMNH Crochet Coral Reef Flickr photostream!

There's a detailed background of the whole basis and etc. of the project here but basically, its an international exhibition of crocheted coral reef faunas...the corals themselves as well as affiliated organisms-mostly invertebrates using hyperbolic crochet.

The Project/Exhibition is WORLDWIDE and "satellite" Hyperbolic reefs are on exhibit in Australia, Europe, Africa and eight major cities in the United States!!

The Hyperbolic Crochet Reef will be here in DC at the Smithsonian's National Museum of Natural History from October 16th to April 24th. Click here to see more!
One of my enthusiastic colleagues allowed me to see some crocheted reef corals and echinoderms she had made....

An assemblage of different types..

The aforementioned green sea star...I "identified" as the big tropical Pacific-Atlantic
Linckia guildingi

(this image from the awesome Guam Reef Life website!)

Here is a crocheted Ophiothrix spp. These are ubiquitous throughout the tropical Indo-Pacific and Atlantic and are readily recognizable by the large number of sharp, needle-like spines that adorn the arms. They frequently are observed living among reefs and other colonial cnidarians.
(this is the Indo-Pacific Ophiothrix foveolata, from Wikimedia Commons)

Here is a diadematid, but probably the long-spined black sea urchin Diadema. One of many urchins which are important herbivores feeding on algae while protected by its long-sharp spines.

This next one is near and dear to my heart and has become a beloved echinoblog feature! The Giant Green Fish-eating ophiuroid-Ophiarachna incrassata!!! Which you can go here to see the full story!

Some fun, fuzzy crocheted Fire Urchins (Asthenosoma spp.)!!

A brittle star whose name escapes me...

and here to round out the hyperbolic reef sneak peek are some actual CORAL type things!

...with hopefully more to come!