Tuesday, June 25, 2013

Starfish with Babies! Brooding Behavior & Pseudocopulation Revealed!

Today: BROODING Juveniles!  Wait, What?  No, NOT like this
Seriously! This is one of the top images that comes up in a Google search for "brooding"
I meant Brooding juveniles like THIS!
Diplasterias brandti
from the Smithsonian NMNH USARP
In other words, these are "baby" starfish that are cared for by the mother until they are ready to head off ont their own. Parental investment resulting in a succesful offspring. 

Sometimes starfish (and indeed most echinoderms) can appear kind of alien. No head. Mouth on the bottom. 5 part radial symmetry. Strange adaptations. All kind of weird sometimes.

So, I suppose its appropriate that the WEIRDEST of ALL echinoderm (and starfish) behavior is that starfish have this almost mammal-like (or at least, vertebrate like) behavior!!   Some starfish species will actually brood and carry little starfish just like the cutest little furry thing you can think of!

Now, most starfish have a fairly straightforward reproductive cycle.

Eggs and sperm are ejected from the males and females-they fertilize and go on to form larvae which swim in the water developing through different stages, eventually eventually settling down onto the bottoms and growing up to become proper "adult" starfish.

But many starfish species stray from that typical cycle, and somewhere between the time the sperm fertilize the eggs and the settled "babies" are established the whole life cycle CHANGES to give you this:

Yes. Tiny baby or small juvenile starfish which are held by the mother around the mouth! (this varies as we'll see). Why do some starfish do this?  And not the more 'typical' behavior?

Scientists have known about brooding behavior in several species of starfish since the 19th Century but only recently has there been the extensive observation and insight to finally piece together the complete story!

The Story of Leptasterias polaris
Information herein is based on a paper by Jean-Francois Hamel and Annie Mercier at Memorial University in Newfoundland. which you can find (here) in Biological Bulletin from 1995 (vol. 188: 32-45)

They studied the large, Arctic/subArctic 6-rayed starfish Leptasterias polaris which occurs in the North Atlantic, Arctic and North Pacific Oceans.
Image by Claude Nozeres  from the Canadian Registry of Marine Species
Hamel and Mercier's paper exhaustively studies L. polaris' complete reproductive cycle, which pretty thoroughly documents the reproductive behavior in this species.  Bear in mind, that this starfish has been known since 1842 and yet our knowledge of its reproduction has only come to us recently (published in 1995)!

Information on brooding remains of interest-but the behavior and its evolution is poorly understood.

Figure 1 from Hamel & Mercier 1995
 As a prelude to the actual spawning there are massive aggregations of these animals. They're involved in an unusual behavior known as pseudocopulation. There's no penetration or combination of sexual organs, nor is there any actual spawning. The animals all just get together into a big pile. Sort of preparation for the main event.

Bear in mind, OTHER than during mating season (November to February), these animals all typically ignore or even avoid one another.

Many echinoderm species practice pseudocopulation which I've written about here. Its not always clear why different species pseudocopulate. But one thing seems clear: It helps the chances of their sperm and eggs get together.

2. Spawning! There were no pics of actual Leptasterias spawning, so here instead is a closely related Asterias. I have discussed this spawning on armtips position here. It is observed widely across cold water and tropical species.
spawning starfish
Image by Tom Ashton
Spawning in Leptasterias polaris males begins as the water gets cold, about 2 degrees C. 

Sperm (male cells) are negatively buoyant, or in other words, they sink to the bottom and form sort of a film. The sperm then go dormant until they come into contact with the female's eggs..

3. The Female Pinwheel formation. Stimulated by the males, and following the deposition of sperm on the bottoms, the females proceed to eject the eggs onto the sperm so that fertilization can proceed.

The deposition of the eggs onto the sperm re-activates the sperm allowing them to combine and fertilize.

During this phase, the females adopt this "pinwheel" formation
From Mercier's L. polaris site
Here (from Figure 5 in Mercier & Hamel) we see a close up of eggs UNDER the female in C. Which then grow up into the cute as the dickens starfish in D.  Growth was after about 5 and half months.
4. After fertilization, development proceeds. Here's a summary panel of the different stages. The top row is the developing embryo. It continues through different stages until it reaches "J." 

At that point the animal is practically ready to move off on its own..
Figure 9 showing development from embryos to small starfish 
Interestingly, Hamel & Mercer found that the development proceeded on its own if the embryos were unbrooded.  They suggest that brooding is behavior which protects the embryos/juvenile starfish from debris and other materials. Animals observed in the field were clear of excess materials.

Protection was also a likely consideration since unprotected embryos/juvenile starfish were rapidly devoured by sea urchins or other grazing animals if they were not protected by the adult. 

 The whole cycle is sumarized in this convenient cartoon!
Figure 4 from Hamel & Mercier 1995
There were MANY more details! If the topic of brooding interests you I urge you to check it out!

BUT That's NOT the end of it!  

5. Brooding is diverse.  SEVERAL different species of sea stars brood. Almost all of them are either cold-water species, living in the deep-sea or at the poles. Sometimes brooding is in temperate water species.. But typically not in the tropics.

Brooding also takes different forms. The oral 'mouth' or gastric brooding mode is but one kind. Here is Diplasterias from the Antarctic!  MANY starfish in the Antarctic brood juvenile starfish!
Diplasterias brandti
from the Smithsonian NMNH USARP
For example, in the suspension feeding brisingids, the Antarctic species Odinella nutrix, broods babies  in special chambers made from the arm spines present between each of the arms.
There is the strange Japanese/Russian/North Paciic Trophodiscus (go here to see more) Juveniles are brooding on the TOP of the animal among the spines (called paxillae) that compose the surface of the disk.
Here is a living specimen. Image by colleague Yoichi Kogure!
Close up
And then there's Tosia neossia, recently discovered in Australia. This species broods but without actually keeping the babies physically on the body. They are kept spread out near the animal... See the orange dots in the picture below?  That's the juveniles...  I wrote about this species here.
Here's the tiny Tosia crawling larvae!
And in the deep-sea, there is the weird "sea daisy" Xyloplax!
And that's not to mention brooding in sea urchins, ophiuroids, crinoids and sea cucumbers! and MANY other invertebrates!  Starfish brooding is just the tip of the iceberg!

Tuesday, June 18, 2013

Feather Star Color Bonanza!

Feather Star
A key lime colored crinoid by Frederique Jaffeux, South Ari Atoll in the Maldives
This week, some brightly, eye-jarring crinoids in mind-blowing COLOR! What are crinoids, aka feather stars?  They are echinoderms that hold their feathery arms up in the water and pick food out of the current as it flows through/past them!  Want to learn MORE about crinoids? Visit this awesome site by Dr. Chuck Messing!

Purple and white feeding fan of a feather star from the Maldives!
Crinoid Fan
Image by Bil Stohler
Here-some brightly colored blue feeding structures called pinnules are seen on the arm...
blue crinoid
Image by mimimoyer
A gorgeous crinoid from Okinawa withdrawn into itself
Feather star - in protection mode!
By Okinawa Nature Photography
A stunning green crinoid from Okinawa.
( Oxycomanthus bennetti ) feather star- okinawa
By Okinawa Nature Photography (Shawn Miller)
Stunning orange..
Feather Star
Image by Henry and Tersia. Borneo.
Black and White on a red sea fan.
Crinoid on Seafan
Image by Randapex
Macro of Blue Oxycomanthus arms. fr. Bali.
Just a crinoid (Oxycomanthus sp.)
Image by Arne Kuilman
Blue crinoid in repose fr. Indonesia.
Koala Crinoid 2033
Image by Courtney Platt
Black & White Crinoid from the Philippines
black 'n white feather star
Image by Mona Dienhart & Chris Lebas

There is a fish in this picture! Can you spot it?
Crinoid clingfish (Discotrema crinophila)
Image by Arne Kuilman
A crinoid in a lovecraftian pose!
Crinoid Flexing
Image by Eddy Wong

Tuesday, June 11, 2013

The Importance of Sea Cucumber Poop!

20111021-143924-Canon PowerShot G12-0720.jpg
Awesome pic by Mevallee
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..

I have written about the importance of the poop of other echinoderms in prior posts-particularly this one about green sea urchins (Strongylocentrotus droebchiensis)

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
2008-11-26 SAPONA WRECK - Sea cucumber poop
Image by scuba.linda
A paper by Kenneth Schneider (Stanford University) et al., including echinoderm researcher Maria Byrne's  was published in the Journal of Geophysical Research (2011. 116: G04032)  received a lot of press, such as this account (in Australian Geographic) and this one (which has an interview with Byrne) about how sea cucumber "poop" is important to geochemical processes on a coral reef.

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!

A recent paper in PLOS one from Thomas MacTavish and colleagues in New Zealand studied a local sea cucumber Australostichopus mollis and how its presence affects the nutrient cycling in its surroundings.

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
Image by Jeremy and Christine
Papers such as the one above, this one focusing on the tropical Stichopus japonicus and this one on Parastichopus californicus in cold-temperate waters all show that many people have picked up on the fact that sea cucumbers are useful animals for breaking up environments that suffer from being choked in nutrients.

Eutrophication-the overabundance of nutrients resulting in undesirable growth of algae and hypoxia-is a common problem in aquacutlure ponds.
Sea Cucumber aquaculture
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!)

The nutrient cycling role of sea cucumbers has been observed as an important part of ecology. One post I put up awhile back shows that the presence of sea cucumbers leads to more productive sea grass!  and thus a more diverse and healthy tropical ecosystem.

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.

Most of their overall morphology seems devoted to processing mud..in one end and out the other...
We add to that another spin!  There are whole microbial faunas that live INSIDE their guts! Go to these past posts to read more about them..

Remember just how abundant these can be in the deep sea. Some occur at a density of 220 individuals per square meter!

How much of this fauna comes out in their poop?  How does it contribute to the local environment?

Tuesday, June 4, 2013

FIRE Urchins! Brilliant Shallow water cousins of the "tam o shanter"/pancake urchins!

Fire Urchin
Image by Aboireoujtulchien
Last week I reviewed deep-sea echinothurioid urchins aka the "tam o shanter urchin" aka the "pancake" urchin, etc., etc.  I spoke of these more generally in an earlier post. But for some reason I've not had a chance to really showcase their shallow water relatives!
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.
Astropyga radiata
(image by Ben Naden)
I've discussed Astropyga on the blog before (here)...

These urchins all belong to the genus Asthenosoma which includes six species spread throughout the Indo-Pacific region.  Here's a neat video that gives you an idea of what they look like..

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.
Asthenosoma varium
Image by Ben Naden
Some video!
Compare to the walking spines on this deep-sea echinothurioid.
Spiny sea urchin
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...
fire sea urchin
Image by JianXu
Some workers have hypothesized that the poisonous spines in deep-water echinothuroids function as hypodermic needles (here by Roland Emson & Craig Young)

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??
fire urchin IMG_6889
Image by Bruce Magun
Fire urchin's spines
Image by Daniel Stassen

Close ups! showing some of the brillaint colors, spine patterns and etc.. I suspect most of these are Asthenosoma varium
Fire urchin!
Image by MerMate
Image by Daphna130
Fire urchin
Image by lupopeye
Magnificant Fire Urchin
Image by maractwin
fire urchin
Image by Nick Hobgood
fire urchin
Image by B. Maither
Fire Urchin Close-Up
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...
Foto-2008-05-08 21.31.25
Image by Key of Life
Here are the spines..still basically the same but different color and slightly different shape..
Asthenosoma marisrubri
Image by Le Congre
Asthenosoma spp. showing many different colors...
Coleman Shrimp and fire urchin
Image by S1mon Mar5h
Image by Clark Chang
IBAb-292 Fire urchin, Asthenosoma varium
Image by Jesse Claggett
Fire urchin
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...
Coleman shrimp
Tiny Shrimp
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....
Ctenophore on a Fire Urchin
Image by Mark Atwell