A sea urchin that eats.... WOOD???

(from the MBARI 2001 Mendocino Cruise)

Today there is weird deep-sea sea-urchin fun! This great but kind of tucked away paper by Pierre Becker et al. published in 2009 in Les Cahiers de Biologie Marine (50: 343-352) reporting on Ind0-Pacific sea urchins from deep-sea wood falls!

What is Asterechinus elegans??!!

In my experience, the first indication that you've got an interesting story is when you've got an unusual critter that no one's ever heard of...

Case in point: According to the NHM echinoid site, Asterechinus is a member of the Trigonocidaridae, a family SO frakkin' weird that I had never even heard of it or Asterechinus before!
And since the database picture is based on scanned images from the original description and figures by Theodor Mortensen in 1942, the species is rare enough that pictures were NOT immediatley available! And for the NHM database...that's sayin' something!

So, from the paper's Figure 1A comes what is likely to be the FIRST live picture of this animal since 1942 (over 65 years!). Its a small species with the largest never exceeding 25 mm. And look! It lives on...wood!

(Figure 1A from Becker et al. 2009)

These were specimens collected by the French BOA I and SANTOBOA cruises in 2005 and 2006 respectively to the Vanuatu Archipelago. Apparently, a great deal of woodfall organisms were obtained...One of which is written up here..

Here's a deep-sea log to give you kind of an idea of what deep-sea wood looks like..

(from the MBARI 2001 Mendocino Cruise)

So before we start on the next section just a brief bit of background- "Wood fall ecology" is part of a relatively new part of marine ecology, including the study of whale falls that studies the influx of massive amounts of organic nutrients to the seafloor's bottom. More on whale falls can be had here.

(from the Census of Marine Life ChemoSynethics site)

Because the deep-seafloor lies so far below the sun's immediate influence, it can be relatively poor in nutrients, making ANY kind of potential nutrient deposit, such as a dead whale, unrooted kelp, trees, etc. a BIG event.

A succession of unusual faunas, composed of both fishes and invertebrates, usually springs up around these deep-sea oases when they form. As it turns out, this urchin forms a member of this fauna.
Other wood-related echinoderms include the weird-enigmatic sea daisy Xyloplax!

It Eats Wood!!! (aka Xylophagy!)
So, upon collection and preservation, they opened the specimens up and looked at the guts-and lo and behold! The guts of these critters were FILLED with wood!! To quote the paper

Observations on the gut content of all individuals (n=20) revealed that they were mainly composed of numerous wood fragments of different size, shape and colour. For instance some were small light cubes, while others were large dark twigs of up to 7mm long.(!)

Although most sea urchins are known primarily as herbivores, they-like many other animals- naturally LACK the ability to innately digest cellulose from trees. And so, Becker et al. cultured and analyzed the microbes in the gut and came up with this...

There was FILAMENTOUS BACTERIA in their guts!! And all of it was in contact with the woody food in the urchin's intestine...

(from Fig. 2C from Becker et al. 2009)

Tests of these bacteria revealed them to be composed of a variety of bacterial types, including Proteobacteria, Planctomycete, Firmicutes, Cytophaga-Flexibacter-Bacteroides, and Actinobacteria. These were all compared against other known marine bacteria using DNA phylogenetic analysis. And it turns out that the bacteria had CLOSE relationship to a bunch of veeerrryyy interesting other bacteria including

1. bacteria from the gut of other xylophagous (wood-eating) animals
2. bacteria from sulphide-rich environments (such as big dead whale falls)
3. mangrove soils
4. marine sediments from hydrothermal vents & cold seeps!!

Why is # 4 important? Bacteria function in vent and seep animals to help process toxic substances, such as sulfide, into digestible form in order for the host to process the nutrients. Closely related organisms often share similar qualities...

Although the authors did not have the exact and complete story, the data above, in addition to other elements of the intestinal bacteria flora all STRONGLY suggests that Asterechinus elegans may host a bacterial community in their guts which they use to aid in wood digestion!!

What other animals use a microbial flora in their guts to aid in digestion?

Termites!
Cows!
and People!

(this image from Nature.com)

Finally...if these deep-sea urchins EAT wood..Do they also eat....WITCHES?

Hawaiian Deep Sea-Urchins!!! Below the Surface of a Tropical Paradise!

So, following up on the Hawaiian deep-sea starfish post from a few weeks ago...I thought it would be cool to show some other echinoderm diversity...and who doesn't love sea urchins???
A brief background on where these pictures came from... These were ALL taken by the Hawai'i Undersea Research Laboratory (HURL) at the University of Hawai'i at Manoa and are all species that live in deep-water in and around the Hawaiian Islands. HURL operates two manned submersibles..the Pisces V and the Pisces VI.
I went down and deep-sea stalked my echinoderm loves in the Pisces V back in 2000. The following are not images from that expedition but a mix of pix from past voyages of HURL's Pisces V submersible... Thanks to Chris Kelley at HURL for allowing me to use them!

1. Aspidodiadema hawaiiensis. Here's a neat species that is also observed in the Bahamas. It has these long freaky spines, which they use to MOVE.

These urchins remind me of the giant black spy spider robot from Johnny Quest....


2. Phoromosoma bursarium. What survey of deep-sea echinoderms is complete without some echinothuriids?? I wrote up a blog on these for Deep-Sea News awhile back as one of the 27 BEST Deep-Sea species (it made the top 10!).

Basically, these are weird urchins that walk around on hoof-like spines. Some genera have these big puffy sacs of unknown function.
But one thing I HAVE experienced from firsthand observation-those spines on these critters? They STING. A colleague of mine at MBARI experienced this during the North Pacific Expedition last year.

3. Chaetodiadema pallidum. There's not very much known about this species, but in and around the Hawaiian region between 50 and 402 m on fine sediment.
These can be VERY abundant... and bringing up a bunch of them doesn't do them justice when they are observed on video arranged in these almost unnatural distribution patterns... spooky!
Who needs science fiction when you've got reality?

4. Chondrocidaris gigantea..Speaking of freaky... Here's one of the shallower-water urchins that you see in deeper waters.. Note that the spines are completely covered over by overgrowth..sponges or other encrusting invertebrates, perhaps?

In this species and other cidaroid urchins (you'll be seeing these below) the spines LACK epidermis and you get all kinds of weird things growing on them..

Here's a little bit I wrote up on them last year...(a bit dated by the holiday theme)
5. Prionocidaris hawaiiensis. Another urchin about which we know very little...
Except that we know where they occur in 92-214 meters? They are VERY abundant!
6. Histocidaris variabilis. What's weird with this one? It has BARNACLES that grow on the spines!! Similar in some ways to the way that Chondrocidaris has sponges and etc. on the spines...
7. Acanthocidaris hastigera. Not much known about this one..but dang, its cool-looking ain't it?
8. Caenopedina pulchella These are neat because the coloration on the spines is actually EMBEDDED in the spine calcite. So, even the preserved ones are red and green!
9. Phrissocystis multispina This is one of the weirder ones... This is a spatangoid urchin (i.e., a sea biscuit) and the group is known primarily from the fossil record.

But the living ones are VERY fragile. I've held dry specimens..and the sediment in the gut can literally cause the bottom of these to fall out from under them.
Thanks to Craig Young, Kevin Ecklebarger and J.L. Cameron we also know a little about its very strange-looking sperm and reproductive biology.

Enjoy! Seeya guys next week!

Cloning As Sand Dollar DEFENSE! Why run & hide when you can divide?

Today, a little somethin' somethin' about a familiar animal..but not quite the way, you're used to thinking about it.. Today's post is based on a new, interesting paper by Dawn Vaughn who is one of the many smart people at Friday Harbor Laboratories! This paper was in issue 157 of Marine Biology of this year (click here!).

Our subject is the familiar sea urchin-the Pacific Sand Dollar, Dendraster excentricus! Here is a good intro page. You can see pictures of the animal alive above..but here is how most people are accustomed to discovering it.. Dendraster is a sea urchin-admittedly a very WEIRD sea urchin. and like all sea urchins (and indeed all echinoderms), the adult forms grow from a small larval stage that is so tiny, this asterisk * is probably slightly larger.

A sea urchin larvae is called a pluteus (plural-plutei)..specifically an echinopluteus (for sea urchins).

(Image borrowed from the Cephalopodiatrist!)

This larval stage floats in the sea before settling down and makes up part of the plankton. So, it was discovered some years ago, that these larvae can be in the water column for quite a LONG time. Months, possibly years. This can be important in the development of the adult..as we'll see..

These can often be food for other creatures that live in the ecosystem at about the same time.. Often, the larvae that float become FOOD for other organisms, such as crustaceans and fish.

Recently though, larval life has been thought of as kind of an added "secret" life and are capable of doing much more then simply floating around, waiting to be eaten or becoming adults.

(Image borrowed from the Cephalopodiatrist!)

It turns out that SOME echinoderm larvae, sea stars and sea urchins (probably others) can actually CLONE themselves. That is to say, they can "reproduce" asexually when they are larvae. (Adult sand dollars cannot divide in half and clone themselves in the same way..)

But WHAT would the evolutionary significance of this action/behavior be??? How does it help the animal survive?

In some studies, echinoderm larvae clone themselves when times are good. Food is prime and temperature is ideal.

But what happens we investigate cloning in the context of hostile or high-risk environments???
There are obvious advantages to being able to clone oneself in the face of danger from predators, such as safety in numbers and so on.

To investigate these questions Vaughn set up an interesting experiment.

They cultured the plutei from Dendraster excentricus and cleverly created an experiment that simulated the presence of different, local fish species in the environment!
How did they do that? They isolated and concentrated the fish MUCUS from 2 different species-the stickleback (above) and Dover sole (Microstomus pacificus).

One of the groups was a "control" group-i.e., fish were not encouraged to attack, whereas the other group had mucus introduced as the "hostile" environmental factor.

Vaughn identified the presence of cloned Dendraster based on the the increased density of larvae (these were in a closed area after all) and the presence of larvae showing physical traces of budding. So, indirect and direct ways of determining the presence of "Uncloned" versus "Cloned" Here's what they got...

(Figure 2 from Vaughn, 2010)

Vaughn found that all of the larvae left in the control (without fish mucus to "threaten" them) were much fewer and much LARGER. Mucus-treated larvae INCREASED in numbers and DECREASED in SIZE over the duration of the experiment.

Figure 2 above shows a nice scale comparison of plutei from the Uncloned versus Cloned subjects.

Take-Away Message #1: When threatened, Dendraster larvae are apparently ENCOURAGED to clone themselves more! Cloned Dendraster are smaller.

Vaughn also performed trials where they looked at direct effect that fish attacks would have on the larvae.
On the graph below, the black bars represent UNCLONED larvae eaten whereas the grey bars represent CLONED larvae eaten.

(Figure 5 from Vaughn, 2010)

The UNCLONED (and LARGER) larvae (in black) suffered substantially GREATER losses to attacking fish then those CLONED (and SMALLER) larvae (in grey).

So, the rather strongly suggests that being able to clone oneself (thus creating MORE and SMALLER) individuals is an adaptive defense. (I suppose that's kind of a bummer if you're one of those larger larvae that get eaten though!)

Bear in mind the time scales here also... The asexual cloning doesn't work on an individual-individual instant scale..i.e., fish approaches and larvae splits. But when the fish leaves a mucous presence in the area..it presumably sets all of the larvae on alert to begin cloning themselves.

This can have a potentially important evolutionary and ecological effect. The presence of more larvae suggests that more fish could be present. Is escalation present? What is the effect of having these cloned larvae on the variation and evolution of the adults?