Echinodermata! Starfish! Sea Urchins! Sea Cucumbers! Stone Lillies! Feather Stars! Blastozoans! Sea Daisies!
Marine invertebrates found throughout the world's oceans with a rich and ancient fossil legacy. Their biology and evolution includes a wide range of crazy and wonderful things. Let me share those things with YOU!
Let's just admit it. Poop is awesome. Its natural, all animals do it and its frakkin' hilarious. PLUS its biologically important to everyone so we can't just stop talking about it..
Recent research has brought a powerful spotlight on not just the ecological, but the overall, importance of sea cucumbers to the environment. Sea cucumbers occur all over the world and at all depths. Often, when present, they are abundant or at least a significant part of the fauna present.
But the key dynamic present to their importance is that they cycle or process what they eat and what they defecate contributes to the health of the habitat they inhabit.
1. Sea Cucumber poop buffers against ocean acidification on coral reefs
I realize that articles about "coral reefs saved by sea cucumber poop" sound kind of silly on the surface, but read and understand below.... (note also the Journal of Geophysical Research? Important stuff gets put in there.)
Coral has to develop or accumulate calcium carbonate, which is the mineral used to compose coral skeletons, at an equal or better than the rate at which the coral loses calcium carbonate via erosion, natural dissolution, etc.
A survey of the sea cucumbers Stichopus herrmanni and Holothuria lecuospilota in One Tree Reef, Australia showed that the sea cucumbers could digest and dissolve so much of the adjoining sediment and rubble (ie the sand) that they actually contributed up to 50% or MORE of the total amount calcium carbonate dissolved over a night time. Presumably this was made available for coral to use for reef development.
Chemically, calcium carbonate is very alkaline or basic. So, sort of like an antacid. What do you do when you have stomach acids that are misbehaving? Drop some of those tablets to "cancel" out the acidity.
So, sea cucumbers contribute calcium carbonate to the coral reef's "chemical budget". They act like a natural antacid to neutralize other acidic environmental sources. Under normal conditions, there's an equilibirum. The abundance or number of sea cucumbers can affect this. Thus, in theory, MORE sea cucumbers might produce so MUCH alkalinity (or "basic" poop to the water) that conceivably they could function as a control or at least a buffer against increases in more acidic sea water. This obviously is important when you consider ocean acidification resulting from global warming. Sea cucumber poop is an important part of helping to keep the geochemical balance of a coral reef in equilibrium.
2. Sea Cucumbers EAT tasty bottom poop and clean it up!
Poop is processed into useful nutrients! Over abundance of nutrients (i.e eutrophication) is broken up by sea cucumber feeding!
MacTavish and his colleagues studied a nutrient-rich environment covered by algae, mussel feces and other nutirent-rich goodies. Under normal circumstances, these would build up bacteria, ammonia and other factors creating conditions that contribute to the growth of algae, which ultimately chokes everything else out (aka eutrophication).
But you put a sea cucumber into these settings? They LOVE it! They eat and all sorts of good things happen:
Bacterial abundance increases
Organic material (i.e., the goo) begins to decompose more quickly
Organic materials are redistributed from the marine sediments into the water
Sea cucumbers help to break down organic material and redistribute the nutrients! The poop is an important part of that process.
This has implications....
3. Eating good poop cleans up aquaculture environments
Eutrophication-the overabundance of nutrients resulting in undesirable growth of algae and hypoxia-is a common problem in aquacutlure ponds.
Image by Smartfish-ioc
But putting a sea cucumber into the mix? A critter that LOVES organic nutrients and gooey stuff like that? It would go to town! Cleaning up the bottom and cycling those bottom nutrients... Seems like a win-win solution for cleaning up the bottom of say a fish or mussel farm where feces from the animals accumulate in huge amounts.
So yes. Sometimes sea cucumbers eat poop. And then poop poop, which is probably "cleaner" than what went in the first place...
4. Sea Cucumber poop is good for plants (mangroves, seagrass, etc.), which are part of a healthy ecosystem
Image by Eunice Khoo- "Mermate"
So, by this I don't just mean ONLY the poop-but the animal digesting and then processing the sediment. This follows everything from the above-they break down organic detritus and make the nutrients available to the water column preventing hypoxia and other bad things going down in the sediment...
(its a great video, but I didn't enter the description!)
Think of them as earthworms! go through the bottom sediments, eat all the organics and leave the sediment.. that's sea cucumber poop!
5. Deep-Sea Cukes have pretty diverse microbial faunas that live in their guts! (and thus their poop!)
Deep-sea sea cucumbers perform very much the same kind of function as the shallow water ones. They live in much finer mud and are often rained upon by nutrients from the surface. Many of these critters, such as Molpadia (shown here) live buried in the mud.
Shallow water echinothurioid urchins are "proper" fire urchins. As opposed to these other "fire colored" spiny urchins, such as Astropyga which are diadematoid urchins. A completely different group!!
"Spiny" urchins are distinguished by the presence of an Anal Cone. See that white bulb on top? THAT is where the poop comes out! You don't see that in "proper" fire urchins as we'll be seeing.. Note also that the spines are much longer.
Yes, the colors are a huge shift in appearance, but similar to their deep-sea cousins, Asthenosoma also has the distinctive "walking" spines...
On this image of Asthenosoma varium the walking spines form a fringe around the lower oral side composed of distinctly yellow spines. My understanding is that most of these prefer soft, muddy bottoms.
Image by Ben Naden
Compare to the walking spines on this deep-sea echinothurioid.
Image by NEPTUNE Canada
From there we start to see more differences as the spines seem to be bunched up in bundles...
But they remain venomous...
And if its not clear by now, YES. They're pretty damn venomous. My understanding is that its very painful.. but typically not lethal.
and they certainly do seem like they do, don't they??
Image by Bruce Magun
Image by Daniel Stassen
Close ups! showing some of the brillaint colors, spine patterns and etc.. I suspect most of these are Asthenosoma varium
Image by MerMate
Image by Daphna130
Image by lupopeye
Image by maractwin
Image by Nick Hobgood
Image by B. Maither
Image by Russell Taylor
Here's some differing species from around the Indo-Pacific
From the Red Sea, Asthenosoma marisrubi with a more mellow look...
Image by Key of Life
Here are the spines..still basically the same but different color and slightly different shape..
Image by Le Congre
Asthenosoma spp. showing many different colors...
Image by S1mon Mar5h
Image by Clark Chang
Image by Jesse Claggett
Image by Richard Barnett
What's even MORE interesting? These urchins have tiny critters which live as commensals(?) among the highly poisonous spines! (this neat vid also shows a LOT of close up details) Urchin Riders from liquidguru on Vimeo.
Some of the little buggers actually "hollow" out a space, clearing out spines where they can live! You can see the bare patch on this one...
Image by Klaus Stiefel
In addition to all the various crustaceans, Amazingly. Here is a benthic ctenophore (which I've written about here) ON A FIRE URCHIN!! (the white blobby bits are the feeding tentacles) Mind. blown!! and incidentally.. a likely first occurrence recorded....
Mostly deep-sea urchins found all over the world (many in greater than 1500 m depths-in NZ they range from 100 to 5000 m!), but with some shallow water relatives (aka the Fire urchins, I'll save these for another day)
They often have very sharp and poisonous spines. And yes, the deep-sea ones too...
They "walk" around on the sea bottom with special spines that have hoof like tips
They were described FIRST as fossils and the living animals were found AFTER...
When the animals are alive they look kind of like this:
An Atlantic species by Hankplank
On this purple species from the Pacific (Tromikosoma maybe? this isn't one of the new ones described by Anderson), you can see the white hoof-like spine tips that the urchins use to "walk" along the bottom..
Image by Neptune Canada
Here is a pic showing the oral surface (ie the bottom). The mouth is at center and as you can see it is surrounded by spines with those white "hoof" like tips. These are what the animals use to "walk" along the bottom of the sea floor.
Also by Neptune Canada
Here's the spine close up showing the "walking tip"
But sadly, when they are brought up on the deck of the ship, the water rapidly drains from their very soft body and they are often left as a shadow of their former self....
As a result of this "deflated" appearance, they are often called a variety of names: "pancake urchin", "leather urchin", "bag urchin", or "beret urchin." However in Anderson's new paper he feels a new common sobriquet would be most accurate-the Tam O Shanter urchin!!!
Even alive, looking down on one, you can sort of see the resemblance..(note however this is not one of Anderson's new species)
Image by Neptune Canada!
Owen's paper (here) describes a whopping SEVEN species in two genera. That's pretty significant given that MOST of these urchins were described in the early part of the 20th Century/late 19th.
These were all discovered and described by looking at a variety of different characteristics. Some as straightforward as body color as well as spine shape and location. But some characteristics are more subtle. These are the individual pieces of pedicellariae-little claw like structures that are present on all sea urchins..which were studied using a Scanning Electron Microscope to yield distinct shapes...
Fig. 28 from Anderson 2013
He also reviewed the many echinothurioid urchins in the New Zealand waters, in addition to the seven known species, Anderson described/reviewed a further nine species (7 were new) culminating in a count of some 16 species of these urchins in the region!, including this beauty... Araeosoma thetidis!! (described by Hubert Lyman Clark in 1909)
