SEA STAR DEFENSE! How do starfish protect themselves??

Today's topic: STARFISH Defense!!
Its curious how often this question comes up. People see starfish and other echinoderms that are just sitting there. Echinoderms don't work in our time scale-and to our perception, they just kind of sit there.

Even other echinoderms seem to have the defense thing worked out!

Sea urchins got spines. Like these.

Sea cucumbers got that evisceration/gut spewing thing (uh...I'll describe this later but its just gross!).

Crinoids can get all swimmy and do all sorts of things to escape. Click here to see some.

Ophiuroids got arms they can drop.

But starfish? How are these seemingly innocuous creatures able to protect themselves?
How do they get away? When things come after them? What comes after them?

Today...a survey of what sea stars use to defend themselves against their various predators and adversaries.

What are starfish usually worried about? Usually fish...but also crabs, and sometimes other echinoderms...

1. Chemical Defenses. So, this is the one most people seem to miss, but its probably one of the most important. Most starfish have specific type of organic chemical called SAPONINS in their body wall.
Among animals (saponins are also found in plants), saponins are only present in sea cucumbers and starfish. Saponins are very unpleasant tasting and based on studies, such as this one and this one, are found in the larvae as well as the adults.

So, fishes and other predators basically learn that starfish are just AWFUL. In vertebrates, such as cats and/or dogs eating starfish and being poisoned by sapoinins can cause vomiting, nausea, and other unpleasant effects. Humans should take this hint and go with it...

Some species, such as this Astropecten polyacanthus have kicked their defenses up a notch and instead of (or possibly in addition to?) saponins, their body walls contain the deadly TETRODOTOXIN.

(photograph by Cory Pittman)

Tetrodotoxins have this chemical structure and function as nerve-blockers that can result in a variety of unpleasant outocmes including death. Pure Tetrodotoxin is 100 times MORE poisonous then potassium cyanide.
Tetrodotoxin gets its name because it is naturally occuring in puffer fish (order Tetrodontiformes). Wikipedia has an interesting article on it here.

Chemical defense also include the production of SERIOUS amounts of toxic materials such as MUCUS (grammar factoid! Mucus=noun. Mucous=adjective!) in the "slime star" Pteraster tessellatus (and probably all of its relatives in the Pterasteridae.)
This picture is no exaggeration. I've seen these animals produce BUCKETS of mucus in response to being annoyed. Early studies of Pteraster in the lab showed that other animals clogged by the mucus eventually die, suggesting that its not a substance that likely predators are fond of....

2. Armor & Spines. One of the more obvious features one sees in starfish, especially in tropical species is the presence of heavily developed armor and armament, such as the spines in this Protoreaster nodosus.
To be honest, armor and spines as defensive are usually interpretations of how the body forms function in the wild. Tropical starfish in the family Oreasteridae, such as Pentaster and Pentaceraster (below) almost all have these heavily developed bodies.
One major group of starfishes, the Valvataceans, which includes the Oreasteridae and other starfish groups with heavily calcified bodies, are highly diverse and considered evolutionarily successful in tropical regions, especially in the tropical Indo-Pacific.

Its thought that these armored bodies are part of why these starfish are so successful.

For example, here's the underside of the starfish Tosia. The tube foot groove is flanked by thick blunt spines.

These spines close up over the tube foot groove and clasp together. This is thought to protect the animal's tube feet and soft tissue from small predators, such as little shrimps, worms and fish.

In the New Zealand Pentagonaster, there are big, thick armor plates that cover over the armtips.
These are thought to similarly protect the armtips from fish, crabs, and/or other predators that attack the armtips.

If predation pressure is that much higher in the tropics-that may drive the evolution and diversification of tropical starfish species..

The crown of thorns starfish, Acanthaster planci is a big ol' starfish bad-ass. Its got the morphological defenses...the sharp spines AND it has saponins in its body wall.
Even if you look at something familiar like the intertidal Pisaster live in harsh wave-swept regions and have heavily calcified armor that I would say protects them the elements and other predators.

(this pic from Wikipedia)

3. Regeneration. Finally...most people are pretty aware of how starfish regenerate...


There's a LOT more I can write about regeneration but the video covers the basics...

One interesting point, however, is also brought up by this paper by Marrs et al. 2000 on arm damage in the North Atlantic Asterias rubens.

They hypothesize that larger individuals have "increased mechancial toughness" and that this replaces the shedding of arms (i.e., autotomy) as an antipredator strategy. There may be a size-related decline in the efficiency of the autotomy mechanism through the relaxation of selection pressure (i.e., the influence of predators).
This was an idea applied to individuals within this species..but if true, then large size itself could be another defense!! One possible explanation for why oreasterids are so big?? Or possibly other species?

Starfish "Bones"! Understanding evolution & adaptation from starfish ossicles! (aka "bones")

(what is this thing? see below for the answer!)

So, during a tour I gave the other day, I was explaining just how it was that something as offbeat as studying starfish evolution IS actually pretty similar to anthropology and human forensics.

Or, to put it more simply...what I and some of my colleagues do is really NOT that much different then what they do on the TV show "Bones"...
The premise of the show is that the namesake "Bones" (=Dr. Temperance Brennan) can reconstruct a history of what happened to an individual by looking at and analyzing their bone structure and INFER the history (and thus, the criminal events) of what happened to that individual.
Believe it or not, a starfish (or even a brittle star) is NOT all that much different. Let's take for example, this goniasterid starfish, Ceramaster.
Asteroids (and other echinoderms) are made up hundreds of thousands to millions of small calcium carbonate bits infused with tissue that are made into a living 3-dimensional box aka the BODY of the starfish.
Kind of like those 3-D puzzles that you see around...
These individual pieces, called OSSICLES or sometimes more informally-PLATES compose the body of not only starfish but all echinoderms. It is the arrangement of these plates that allow us to identify and classify them.
Ossicle architecture and arrangement are analogous to the way bones are understood in humans (and other vertebrates). And by knowing where these "bones" (=ossicles) are located, we can use them to reconstruct an animal...and (within limits) its history.
This comes in quite handy for paleontologists who study fossil starfish!

Fossil starfish remains are often broken apart and disarticulated (i.e., they are discovered as individually separated pieces). Trying to put them back together to resemble the formerly living animal can be quite a challenge.

(this chart from Humberside Geologist #12)

There is a HUGE literature of European starfish paleontology that focuses exclusively on individual ossicles like this. One great website with images of individual ossicles and animals can be found here.

In some places, you can literally find bucketloads of individual ossicles! Sometimes they are so abundant, they can actually be used to identify stratigraphic rock layers. Very RARELY are starfish fossils ever found intact.

Okay...so ossicles are nice...but how is that ANYTHING like being the starfish version of Temperance "Bones" Brennan ???

What can you tell about a starfish as it lived from dead pieces?
If we observe how the SAME series of ossicles in parallel position on the animals' body, we can see how those ossicles series change across different species. In vertebrates we would look at how those same BONES have changed across different animals

In other words, how have those bones/limbs have EVOLVED or ADAPTED to different environments.
We can do the same thing with starfish!!
What you're seeing below is the above Ceramaster with its surface body wall completely removed.

That's the mouth at center with each of its five arms projecting from what's called the mouth frame.

Each arm series (kind of like an arm or a leg in a vertebrate) is made up of a very distinctive series of ossicles called the ambulacrals. The ambulacrals are often specific to different kinds of starfish species!
Let's take this Pacific Asterias amurensis for example...
If you take the top off..you see that there's a similar but different structure.

The individual ambulacral plate/ossicle series are made of of much thinner, smaller pieces as you can see here...
These suggest that there is much more flexibility and range of movement in the arm, which is what you would expect for Asterias, which feeds on mussels and other shellfish versus Ceramaster which is more of a less active, sit-on-the bottom type deposit/opportunistic bottom feeder.


In contrast, we look at a very opposite feeding type...the brisingid, filter feeder Novodinia antillensis. I've written up how these feed here...

(Novodinia antillensis from Ocean Explorer)

But long story short, they hold their arms up into the water column to pluck tasty crustaceans and other tiny food out of the current as it flows by....

The ambulacral ossicles on Novodinia look like the vertebrae from a backbone!! These permit the arms to be very long and stable but ALSO to FLEX! and curve into the water.

And finally...just to show you another extreme, here's a pic of Culcita novaeguineae, a living tropical Indo-Pacific "cushion star"

And here is what happens when you cut one open!

Much of the inside is filled with water (i.e., empty) but you've got the massive armored body wall and you actually need a "support pillar" inside the body cavity that connects between the body wall and the ambulacrals.
The mouth frame is pretty thick and robust...and the ambulacrals actually have kind of a special cavity for the tube feet to pull up into when the animal doesn't want any of its soft parts exposed!

The weird insides of this cushion star are actually pretty typical for ALL oreasterids.

So, you could infer from the individual ossicles or even a badly damaged specimen that you've NEVER seen alive before, the possible KIND of life mode it had! Not always...but it is one way to do the job!

For MORE starfish forensics goodness! Check this post from Echinoblog 2008!

Sunflower Starfish Video Day! aka Pycnopodia Power!

(image courtesy of Allison Gong!)

Its been awhile since I've had a chance to share some cool starfish videos and there's some awesome new sunflower star video on YouTube!

1. The "mound" of moving Pycnopodia helianthoides ! A video from the Vancouver Aquarium. Research diver Donna Gibbs was out and observed this spectacular spectacle. I dont' think I've ever seen a huge aggregate of sunflower stars like this before! Literally climbing over each other in high densities. The Vancouver Aquarium folks speculate on temperature or red tides as the cause..I wonder if it might be some kind of odd reproductive behavior. Anyway...its weird and spectacular!


2. Sunflower stars battlin it out! Nuff said!


3. Sunflower star TIME LAPSE turn over. If you don't love watching starfish time lapse-then you have become TIRED OF LIFE!!!


4. Sunflower Stars VERSUS the SCALLOPS!! Watch the Godzilla of starfish terrorize a bunch of hapless bivalves! ha! Silly Scallops!! Watch them RUN!


5. Finally... there's always THIS favorite... Sunflower star clears out the hapless brittle stars and sand dollars around it! THAT is who's boss! All to a hip soundtrack of Vivaldi's Four Seasons!