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!
So, because of the Memorial Day Weekend, the two blogs last week and busy preparations from upcoming travel, here are some "Best of..." links to prep you for NEXT week!
Via the Ocean Portal Question Poll! The WINNER with 26 votes was....
Can sea stars see?
Yes! But perhaps not in the way that you would imagine. Sea stars and other adult echinoderms have what's called pentameral symmetry (although they are bilateral as larvae-that's another story though). This means that they have bodies that project outward from a central point analogous to the form a jellyfish or sea anemone might have.
They lack a head and a centralized nervous center, such as a brain or a head with optic nerves, and much of their sensory apparatus is more spread out along their body.
Sea stars don't have lens-based "vision" the way, mammals or even octopus or insects do, but they can "see" using two main sensory means:
1. There are cells located throughout the skin (i.e., the epithelium or epidermis) on the surface of most asteroids. The full range of function remains to be determined but from what is known they can detect light, physical contact and chemical/chemosensory stimuli from the environment around them.
A range of sensory cells are also strongly present on the tube feet and on the margins of the tube foot groove. Some 70,000 sensory cells per square millimeter have been reported in these areas!!!
2. There is an "eye spot" at the tip of each arm that is located below the end tube foot (aka terminal tentacle) at the animal's arm tip. There are about 80 to 200 pigment cells there that form an optic cushion which can be used to detect light. As a generality, asteroids are thought to be positively phototactic, or i.e., they move towards light although species show huge variation.
From Facebook...
Tammy P. T. Dr. Mah - Have other echinoderm "outbreaks" been observed other than the one involving the Crown-of-Thorns Sea Star in Japan and Australia? Is this very common? Thank you!
In most cases, human influences contributed to the changes in abundance/population density changes. These influences include increased nutrition/primary productivity (as in Acanthaster), species introductions, diseases (some population changes go into decline), or overfishing resulting in an absence of predators.
Certain species may have characteristics that make them more predisposed to undergo population "explosions". So, even though the story and environmental conditions may differ it is possibly an intrinsic quality of differing species that may make it more likely to undergo an "outbreak".
Another example of a huge population boom is in the introduced Pacific starfish, Asterias amurensis from Alaska/North Pacific to the temperate South Australian region.
Basically its story is tied to the huge reproductive output combined with the fact that it has no natural predators...
Here are my blogs on Asterias amurensis.. Part 1. and Part 2.(click and go!)
.... And via Twitter
@oceanelements@OceanPortal Q on CoT: If on a particular dive site n 45 min bottom time you see > 10 CoTs, is that considered too many?
First-one should bear in mind that numbers are relative depending on where you are and an outbreak is related to how many are perceived as occuring "normally." Based on numbers summarized by C. Birkeland and J.S. Lucas's fine book "Acanthaster planci: Major Management Problem of Coral Reefs" seeing 10 CoTS would be closer to a "normal" range.
It should be noted that A. planci do have a behavioral tendency to aggregate when enough of them are around. 25 to 30 A. planci per 10 minute swim might simply be "patchy aggregation". If you are seeing 10 in 45 minutes- I'm guessing that's closer to normal.
One account I read suggested that an outbreak density would be 1150 individuals(!) in 20 minutes of swim or 57 animals per minute! In contrast another suggested that an average of 0.22 starfish per 2 minute tow (presumably pulled by a boat) (=.11 starfish per minute) would be an outbreak. This latter would place your value into the outbreak range but is based on a fairly specific set of conditions that you might not be replicating.
So, estimates vary.
From Neptune Canada:
So this video was sent to me via Neptune Canada with regards to the question of these brittle stars (ophiuroids) fighting over this shrimp for food! Go see this blog I wrote awhile back for something similar
Do they have eyes between their tentacles? How do they charge at each other with such accuracy? Can you offer any insight on sensory capabilities of these brittlestars? (answer is below)
Brittle stars are somewhat similar to sea stars in that they have sensory cells in the skin (i.e., the epithelium) which covers their entire body.
Although some brittle stars can detect light, this species occurs in the deep-sea and its unlikely that light or vision plays an important role in how these brittle stars capture prey. So what does that leave??
Basically smell and touch. Bear in mind that ALL echinoderms are basically big open, porous boxes that that have the outside environment (i.e, sea water) slushing around inside them. And skin covers the inside of their bodies as well!
That means they can sense even the slightest change in the surrounding environment and can follow/detect molecules of attractive or offensive substances much more so than you would expect.
This translates to the fact that these brittle stars can detect that big piece of shrimp "meat" very easily, even though they may not physically "see" it the way that you or I might.
And once they've actually gotten their arms around it-evidence suggests that their sense of physical contact is equally sensitive. Several of them know its there because they can "smell" and "feel" it.
Whew! That's it for questions to the Echinoblog this time around!
Do you have more?
Let me know! and we'll have another Q & A session in the future!!
I write about one of the world's most well-known sea star species, the Crown of Thorns aka Acanthaster planci! So, here on the Echinoblog-I thought I would give you a little something extra about this dazzling and spiny beast!!
An epic skirmish between this huge monstrous toxic, spine-covered monster VS. a crazy colored shrimp and a pugnacious polychaete worm!!
They occur on coral reefs throughout the tropical Indian and Pacific Oceans and occur from the west coast of Mexico and central America, north up to Japan, south to New Caledonia and westward to the east coast of Africa. They are abundant but are also ecologically quite important. Because, not only are they big predators of coral but they are themselves FOOD (and prey!) for other invertebrates in the tropical reef ecosystem!
There are actually a surprising number of animals that feed on the Crown of Thorns Starfish (including giant snails and fish), but today we deal with two tiny but very important predators and the potential impact they may display!
Data for the below comes from work by Peter W. Glynn on populations of Crown of Thorns in Panama (Pacific side) from the Bull. Mar. Sci (1984) and a paper from the Proc. of the 4th International Coral Reef Symposium in Manila in 1981 Vol. 2: 607-6712.
1. The Shrimp!Meet: Hymenocera picta.
H. picta is known commonly as the Harlequin or Painted Shrimp owing to their very eye-pleasing designs and colors..
But this hides their TRUE murderous nature! This species and several of its relatives are predators on starfish and other echinoderms..Here is a video of one in action feeding on a hapless ophidiasterid... As you can see, they are pretty vicious little crustaceans!
It was estimated by Glynn that the attack frequency on average varied between 3.2% to 7.7% relative to the number of sea stars present. (this could be as low as 0 but as high as 20%!)
(Fig, 2 from Glynn, 1981)
2. The Worm!Meet Pherecardia striata- an amphinomid polychaete worm....with a vicious streak!
Pherecardia striata is an opportunistic omnivore/predator, feeding mostly on algae and detritus-but is also heavily into grabbing and eating crustaceans, mollusks and echinoderms (including other species of starfish) as they become available..
Worms such as these can be quite abundant. Although Glynn did not sample the whole population, sampling recovered many individuals. Based on Glynn's sample, there were from 90 to 380 individuals per square meter of reef!!
Similarly, Glynn estimated that the mean attack frequency was about 6.5 % (ranging from 0 up to 25%! of the population studied).
(Fig. 3 from Glynn, 1981)
3. The Action! What happens is this:
FIRST-the shrimp (H. picta) attacks the starfish-tears apart the sea star's surface or dismembering one of the arms. Basically creating some prominent tear in the body wall..
THEN-the worm picks up on the opening and DIVES INTO THE wound/open body wall!!
Pherecardia then proceeds to attack the starfish from the INSIDE!! They enter into the body cavity and begin devouring its various guts! In other words- the pyloric caeca, gonads, water vascular system and so forth..
Sometimes, there can be anywhere from 10 to 18 worms INSIDE a single Crown of Thorns!
4. The Impact!
The relative frequency of COTS that are attacked by both shrimp and worm was pretty low (about 0.6%) but very effective. Based on their observations of wounded Crown of Thorns taken to aquaria, individuals attacked by both shrimp and worms died within a week..
Glynn actually found that the correlation between COTS abundance (i.e., the number of individuals) and shrimp attacks showed an INVERSE relationship (i.e., number of starfish goes down when shrimp attacks are up)!
So, shrimp attacks were MOST frequent when Acanthaster was LEAST abundant.
(there is alternatively the possibility that there was an explanation for the relationship owing to statistical bias of having too few sea stars)
Glynn points out that BOTH Hymenocera and the worm Pherecardia are VERY abundant on the coral reefs in which they live.
So, even if the attacks frequency was not very high-these predators would be very effective and potentially affecting COTS populations (at least in localized regions..)
Glynn goes so far as to imply that populations of East Pacific (i.e., Panama) Acanthaster planci might well be kept "in check" by the constant attacks (and feeding) on the COTS created by being constantly under attack by these tiny but abundant little predators working in tandem!
and if by chance you can only understand tropical Pacific ecology using Star Wars analogs, then you are in luck! Think of it this way...
Millenium Falcon = the Harlequin shrimp Hymenocera picta
X-wings = the worm Pherecardia striata
Death Star= Crown of Thorns Starfish Acanthaster planci
Marc is pictured here holding the calyx of a specimen...
The Where
The specimens were collected from the Admiralty and Scott seamounts north of the Ross Sea, which is on the Australia/New Zealand "side" of Antarctica.
Stalked crinoids are usually pretty deep-and these are no exception. Specimens were collected from 450 to 1680 meters.
Note that this species has a stalk that cements itself to the bottom. So, they ain't goin' nowhere....
(From Fig. 2 of Eleaume et al., 2011)
The Species Name (i.e., the Who!)
This handsome animal was named Ptilocrinus amezianeae for Dr. Nadia Ameziane, the Senior Curator of Echinoderms at the Museum national d'Histoire naturelle in Paris.
(image courtesy of Dave Bowden at NIWA)
Nadia is a VERY busy person. So much so, that even my attempt to photograph her was only partially able to capture her as a high-speed blur!
The What
So, as I've mentioned before, new species are described by a special kind of scientist known as a taxonomist.
These are people who have become extremely well-versed in the scientific "legalese" used to describe a specific species using the very unique language that encapsulates all of the characteristics which make that organism distinct.
I'm not going to try and introduce you-my patient audience! to the finer points of crinoid taxonomy.. but I can say a little bit about the features used..
In addition to some of the general features listed above there are a host of more complicated structures used to tell different species apart.
Crinoid taxonomy is based largely on the combinations and fusions of different kinds of plates as they are arranged on the animal. Like all echinoderms-working on crinoids is like working on a complex 3 dimensional puzzle...
(from Fig. 2 of Eleaume et al., 2011)
For example, the stalk is made up of individual round life-saver like bits... These are present on living animals but are also on Paleozoic fossils and are used to identify fragmentary remains on animals millions of years old..
(from Fig. 6 of Eleaume et al., 2011)
The How Long! (Ecology & Population comments) So, as mentioned in my earlier blog, the time these crinoids have on Earth may be numbered....
First-because of predation- They were observed being fed upon by several other echinoderms...
That includes the relatively common Antarctic species, Porania antarctica, a species that seems to be eating the feeding tentacles and the cup (where the soft guts and so forth are found)..
(image courtesy of Dave Bowden at NIWA)
Another predator is the sea urchin Sterechinus antarcticus
(image courtesy of Dave Bowden at NIWA)
...and are probably fed upon by fish as well...
Second-This species was unusual in that they were able to make specimen AND video observations.
They found that a lot of the observed individuals were all similar-sized adults with few small sized individuals which suggests that there isn't a lot of recruitment (i.e., juveniles replacing adults).
Plus-a survey of organisms living on the stalks (i.e., commensal epibionts), suggests that these animals are pretty old.
(image courtesy of Dave Bowden at NIWA)
Genetics of the sampled individuals in addition to observation of the many broken bases left on the rocks (below) suggests that there were many more that are now gone...
(image courtesy of Dave Bowden at NIWA)
These are all indications that populations of this species are in decline....
Have we discovered this species only to see it fade away like the Titans of old? Or are further populations of this species remaining to be discovered?
This week-thanks to questions from some of YOU-the Echinoblog pubic! I dug up some information on Linckia laevigata-aka the Blue Linckia.
For such a well-known species, I was surprised at how little was known about it..
And so here is the Echinoblog's "Three things you might not have known about Linckia laevigata!"
1. Linckia laevigata's reproductive strategy is NOT well- suited to a heavy fishery.
Linckia laevigata aka the Blue Linckia aka "finger starfish" occurs widely throughout the tropical Pacific and Indian Oceans in shallow-water reef type settings.
Sadly, most people have likely become familiar with this species because its collected and dried in the thousands and made into garishly-colored ornaments, such as the ones below...
Linckia laevigata is heavily trafficked in the aquarium trade and can be seen in many tropical fish tank videos...
Their survey indicates that Linckia laevigata accounts for 3% of the TOTAL global trade in marine invertebrates!!
Most specimens are taken from the wild throughout its Indo-Pacific range. It can be commonly encountered and easy to collect. Few if any are the result of captive breeding programs.
So, even though this species is not eaten-it is harvested and given the sheer numbers of individuals that are taken (even for a common species)-ya' gotta ask the question- "How Long Can that last???"
Yamaguchi both surveyed individuals in the field and also grew out juveniles and inferred growth rates based on the overall changes in size of those lab-grown specimens.
So, it turns out that from the time that a larvae is spawned the average juvenile (larvae) may take up to TWO YEARS for it to actually settle out and transform into an (small) adult!
Plus-smaller individuals were often absent from population surveys-suggesting that the number that reach breeding age (i.e., are "adults") is relatively low.
A large sized animal (and these approach about 1.5 feet in diameter) could easily be several years old...
So-bottom line is that these guys grow slowly and have a low turnover rate with few juveniles ascending into "adulthood" at a given time..
It seems likely that the reason for the abundance of these animals is largely due to long-term accumulation of those adults over time. And when those guys are wiped out-they're gone.
Yamaguchi noted that days after releasing marked individuals for his study-several of the tagged animals had vanished-likely taken by "reef-gleaners"....
2. Feeding & Ecology.
Probably one of the most widespread and incorrect assumptions (like this one) about tropical sea stars, such as Linckia laevigata is that it eats clams and meat in a manner similar to cold-water starfish species such as Asterias forbesi or Pisaster ochraceus. I have complained about this misunderstanding in other blogs..
So, here's the thing-L. laevigata feeds on bacterial biofilm, algae and/or whatever nutritious goo it can get its stomach on. They are considered herbivorous.
This is an intrinsic part of their biology. Some papers such as this one by Laxton (1974-I told you information was few and far between!) determined that L. laevigata's ecological significance may lie in its relationship to become more widespread following algal growth on coral following a big predatory binge by the coral eating Crown-of-Thorns Starfish (Acanthaster planci).
Yes, some of the more experienced aquarists are probably saying "But I have seen and fed this species clam meat (or fish or whatever) before..." And yes-that may be true-but honestly, how long do those animals live after that???
My guess is that feeding L. laevigata clams without any of their primary food-would be like feeding any human pork rinds for a whole year. It might be "food" but it would be a slow death...
3. Linckia laevigata plays host to a multitude of other animals (both parasitic & commensal)
There are actually quite a few OTHER invertebrates that live either as commensals or as outright parasites on L. laevigata.
I've reactions by people that this is some kind of bad thing. Truth is, these critters would only be found on a healthy animal. Discovering one of these is basically like an extra bonus-so, best to leave em' be...
Probably one of the most noticeable is Thyca crystallina-a parastic snail that lives attached to the (usuallly oral) surface of an individual starfish. Data on this relationship can be found here in a paper by Hugh Elder (1979). The snails are attached to the coelom via a proboscis.
Most of these attached shells are apparently female and the degree of infection of Thyca tends to be correlated with the degree of water movement with more active water associated with fewer Thyca per individual Linckia..
Today some cool commensal crustaceans living among feather stars! (aka comatulid crinoids). Crinoids are filter feeding echinoderms that live in the tropics of the Indo-Pacific (and the Atlantic). Some live in the deeps...
Not sure about the comments of the narrator regarding the unpalatabity of the crinoid-but certainly those shrimp get some food out of it... and dang! Look at that camoflage!
Today, I will answer YOUR questions that were asked regarding my recent Ocean Portal Blog via the NMNH Ocean Portal Poll on Facebook as well as questions sent to me via Twitter! 
They are abundant but are also ecologically quite important. Because, not only are they big predators of coral but they are themselves FOOD (and prey!) for other invertebrates in the tropical reef ecosystem! 
Here is a video of one in action feeding on a hapless ophidiasterid... As you can see, they are pretty vicious little crustaceans!
(photo by Terry Gosliner)
(photo by Terry Gosliner)
