Biophysics Meets Old School Taxonomy! Ochre Star Pisaster ochraceus can adapt body shape to wave action!

Image by RJadams55

One of the things I love about biology is when you have an animal which has been studied down to the wire and become so familiar that people take it for granted, and then you discover something completely new about it!!!

And that in turn gives you insight into past events and other things around you. Cryptic? Yes..but I will explain.

This week's post is from Kurtis Hayne and A. Richard Palmer, University of Alberta in Edmonton
who have written a swell, new paper in the Journal of Experimental Biology 216: 1717-1725 (here)
(my thanks to Kurtis for an offprint of the paper).

It studies the reaction of the classic workhorse starfish Pisaster ochraceus as it reacts to one of the harshest of environmental stresses:  the ocean itself! WAVES!!      SPLOOSH!

Image by Lance and Erin Willett

Details....
Hayne and Palmer collected numerous individuals in and around Barkley Sound near the Bamfield Marine Sciences Center on Vancouver Island.  Individuals were collected and measured to assess values for drag and lift. Some were tagged and returned to the field for various field transplant experiments (look below).

Specimens were also surveyed in the field and correlated with the power of various wave forces.

Their findings!

1.  Sea stars in wave-exposed sites had narrower arms and were lighter per unit arm length than those from sheltered sites. On average, animals from the most exposed sites were 12% narrower at the base compared to the most sheltered!

2. Body form was tightly correlated with the maximum velocity of breaking waves across four different localities and over time.

3. Sea stars were transplanted between sheltered sites to more wave-exposed sites revealing that they became LIGHTER per unit arm length, developing narrower arms after 3 months! There was a tight correlation between water flow and the body shape which strongly supported the idea that wave force was affecting the body shape.

This figure 7 very nicely summarizes their findings. The animal on your left ("A") is an example of an animal from "most sheltered" going right to the one on the lower right from "most wave exposed".

 and the small box "D" even shows the extent that the abactinal spine/granules show density and a heavier degree of calcification between a sheltered (orange on the left) vs. an exposed (purple on the right) individual.  

The exposed form below is overall smaller in size, weigh less, and with a higher aspect ratio (arms narrower, etc.) and with a more dense skeleton.   
Dynamics 
1. This is thought to aid the individuals in a wave-exposed environment from being washed away. Not as much lift and not as much drag.
2. The heavier granules offer more protection against the crashing forces of the waves.
3. BUT, having a higher aspect ratio comes with some costs:
          a. such as being more prone to overheating. Sheltered are much more effective at resisting
              overheating and water loss. Although heating may be offset by cooling temperatures from
               waves and such..
          b. having smaller areas available for gonads. This results in lower overall production of
               reproductive material and so on..

Image by jkenning


Image by Shannon Robalino

The protected body form
These make more sense in protected areas away from the harsh, crashing wave-swept regions:
Some dynamics...

1. Larger animals are more likely to be caught and washed out to shore. (greater drag and lift at play)
2. BUT the larger, thicker size involves more water retention and thus better thermoregulation and better cooling.
3. Greater volume for gonads! More potential offspring!

from Scenic Beach State Park in Washington

From Samantha Russell


Bear in mind-that in order to test these interpretations, animals were actually transplanted between protected vs. wave-swept areas. Transplanted animals (from protected to the exposed wave-swept areas) decreased in mass and increased in aspect ratio over time. 

Environemntal factors directly affected the body shape of ochre stars!

Biophysics Meets old fashioned Taxonomy!

Probably the neatest footnote to all of this was that these differences in different forms of Pisaster was observed by several naturalists in California, early in the 20th Century.

The great Stanford starfish biologist and Director of the Hopkins Marine lab, Walter K. Fisher identified several "forma" or distinct morphological variants of Pisaster ochraceus in his giant 3 volume monograph documenting and describing the asteroids of the Pacific Northwest from 1930.(sadly the Asteriidae is not in the volume linked).

Fisher even observed that the differences in three of these forma seemed to be based on the degree of calcified skeleton, i.e., how built up the spines were...

It is difficult to escape the inference that the characteristic small spinelets of the abactinal area are correlated with queit water, but that this is ot the only factor is evidenced by the presence, along with confertus, of forma ochraceus and nodiferus, the latter found on open coasts and also in deep water (Monterey Bay).

The variant nodiferus is Hayne and Palmer's "exposed coast" morphological form. Fisher's comments about the inconsistency of abactinal spinelet shape/size suggest there remains even more variation and other factors to consider in future studies..

Sometimes, these "forma" turn out to be distinct taxa-perhaps subspecies or species. But sometimes its just some variation in body form in reaction to the environment.

Just as if we took a flabby, couch potato from his comfy TV room with silk bedsheets and put that person into an underground mine to dig minerals for a living. We would perhaps see changes in musculature, bone structure, and maybe even hair/eye color.

So there you have it! A cool convergence between a modern biophysics story with a fun footnote from classical taxonomy/natural history!
Are these considerations we might apply to other intertidal asteroids in similar settings? (Stichaster australis from New Zealand). Image by Jon Mollivan


Want to know more about the Ochre Star: Pisaster ochraceus?
 Here's my post about Pisaster ochraceus ecology and role in climate change. 

and what explains all the color variation in Ochre Stars?? (here)

Want to see a sea urchin that lives in a high-energy wave swept environment? See Colobocentrotus! The Shingle Urchin.

Tales from the Intertidal! Algae+Snail=Protection from Big Mean Starfish!

California's rocky intertidal (and subtidal) zone is a wonderous place!

A countless host of invertebrates and other organisms co-exist here-a rich ecosystem that is one of the most distinctive and well-studied marine ecosystems in the world.

(From CSU Fullerton's website)

Much of that richness comes from understanding the complex interaction between the species which live here.

The various "stories" or natural history that have resulted from the feeding, defense, behavior, and reproduction of MANY species has laid the foundation for well-grounded ecological understanding of the many organisms that live here. Few places in the world have such a well-understood and rich fauna.

Here is ONE of those stories!

Today's blog is based on research by Carol Thornber at the University of Rhode Island
in a 2007 issue of Marine Ecology 28: 480-486-Associational resistance mediates predator-prey interactions in a marine subtidal system.

Thornber began with an interest in the ecological effect of epibionts on ecological interactions.

Epibionts are organisms that live on the surface of another living organism, so a kind of commensalism. Examples might be barnacles on whales or perhaps the worms and other encrusters on these cidaroid sea urchins.
It turns out that there's a pretty neat little example of how epibionts affect an important interaction between the Brown Turban Snail and its sea star predators!

The Players
Thornber focused on the Brown Turban Snail: Chlorostoma (cited in the paper as Tegula which is a synonym) brunnea.

(from the very helpful Walla Walla Washington site)

The Brown Turban snail is often covered with different types of crusty or coralline algae that give it a rougher "covered over appearance".

This isn't a brown turban snail...but it gives you the general idea.. A full "leaf" of coral is off to the right side..

(from the Stanford site, phoyto taken by J. Watanabe)

The image below isn't the Brown Turban snail-but it gives you the general idea. Note the red/pink crustose algae at the top!

(Calliostoma montereyi from the Stanford site, photo taken by J. Watanabe)

Questions:
#1-How common is it to find Brown Turban Snail (i.e., C. brunnea) shells covered by algae? and how does this relate to the abundance? Or in other words does more starfish correlate with MORE or LESS coraline algae on shells ??
#2-Does the presence/absence of algae covering the shell influence feeding preferences of two predatory starfish??

Specifically..the intertidal Pisaster ochraceus
and the shallow-water subtidal sunflower star Pycnopodia helianthoides!
In Answer to the first question ...
-Apparently >60% of of snails were at least 75% covered with one or more species of crustose algae. A minority of snails (35%) wer completely covered. So covering of shells with the red/pink algae is pretty common.
Fig. 2 from Thornber's paper shows the correlation of density of Brown Turban snails relative to the density of Pisaster and Pycnopodia.

She found that the density of the snails was driven by the abundance of predatory sea stars-specifically Pisaster !!

Lab Experiments (2nd question)! How will Pisaster and Pycnopodia feed on algal covered shells??

Based on her Fig. 3, it turns out that shells that LACK any kind of the algae included (coralline and crustose) are the MOST preferred by the two predatory stars tested!

The bar graph below shows the greatest % of C. brunnea was fed upon when the shells were bare.
Pisaster ochraceus was nearly THREE times as likely to consume BARE C. brunnea than those covered by algae.
Pycnopodia ate FOUR times as many BARE snails as those covered with crustose coralline algae.
The results support an interesting idea-the crusty/red algae that is present as an epibiont on the shells seems to discourage predatory starfish from feeding on the snails!

Thornber discusses some dynamics...

1. The algae may provide camoflage against visual predators, such as crabs, octopus, fish, etc.

2. It is unclear if the distribution of the algae is somehow influenced by the snail or some other non-random factor.

3. What makes the algae so "discouraging" to starfish? Possibly the production of chemical defenses..

Or it could also be that the rough surface itself creates an unpleasant or irritating sensation to Pisaster and/or Pycnopodia.

The "mollusk escapes starfish predator" theme is an old one. Its an important ecological interaction that has been at the center of many ecological surveys.

From a purely behavioral escape point of view though, it joins the ranks of such noteworthy strategies such as this...

clam escapes from sunflower star!

and this! Scallops escape!

Why is Pisaster ochraceus (aka ochre star) so many colors? AKA they are what they eat!

(image by Nancy Sefton, NOAA Olympic Coast page)

So, early in my career during my various internships and volunteer time, I spent a fair bit of time at the educational tidepools exhibits at the California Academy of Sciences and Monterey Bay Aquarium.

One of the most common questions I would get about the commonly encountered "Ochre Stars" (Pisaster ochraceus) that live on the west coast of North America.

"Is there any significance to the color?" (or some variant thereof)

Well, its taken nearly 15 years but FINALLY...I can answer this question! I thank a neat paper by Harley et al. 2006 in the Biological Bulletin, which is available via Open Access!

So, here's the story!

This species lives along the coast from Alaska to California, including British Columbia, Washington, and Oregon.

These animals have a brilliant and very distinctive suite of colors that stand out. These include

PURPLE...

(image from Wikipedia commons)

BROWN (or RED)

and... ORANGE...and in fact, the species epithet, "ochraceus" in "Pisaster ochraceus" or the common name "Ochre Star" refers to the yellow-brown color, which was probably the living color of the the first specimens that were described of this species.

It turns out that the colors DO indeed VARY with region. Different places along the west coast have variable colors. Of populations they surveyed from 31 sites in California (North & South), Oregon, Washington, British Columbia, and Alaska. (diagram below is NOT proportional)

Across the surveyed sites, they found that on the whole MOST of them were brown-reddish with a relative minority of orange colored members as part of the population.

Curiously, those in certain isolated channels..in Georgia Strait (British Columbia) and Puget Sound (Washington) were 95% PURPLE!!

(image from Wikipedia commons)

In addition to color, they further examined other factors: food, size, and injury. And ran them together with a cluster analysis.

And they got a diagram that showed overall similarity between members from each of the different sampled study sites.

(Fig. 3 from Harley et al., 2006)

There was a close association between all of the populations in California, Washington, and Oregon (seems like Alaska was omitted).

The Georgia Strait and Puget Sound populations (the purple ones) clusters together AGAIN.

COULD these purple populations be something new or different???

A logical question to ask at this point. Did this separate purple population or ANY population of this species have enough separation or structure to warrant consideration of a new species??

So, The study looked at population genetics of P. ochraceus.

That is, the amount of genetic structure was present in the various populations within the species across its distributed range.

(image by Nancy Sefton, NOAA Olympic Coast page)

Essentially, there was NO structure of populations across the range.

That is to say, that an individual from San Diego (southern range) and an individual from Alaska (northern range) were really NOT all that different. Gene flow between populations remained high (that is, no subset of the gene pool had been significantly isolated)

They found NO "obvious" relationship between color and each population.

So, to put it in much simpler terms- There is no color (or other) subset of this species that has become isolated enough that its about to become a separate species or even a genetically separated population.

WHAT's going ON with the PURPLE ones then????

One of the coolest conclusions of this paper was that COLOR in P. ochraceus is probably related to what individuals of this species ATE.

So, it turns out that individuals from California, Oregon, and Washington?

They enjoy eating The mussel Mytilus californianus

(image from Wikipedia commons)

...and now we get to the PURPLE ones from the isolated inlets in Georgia Strait and Puget Sound. What's different about these isolated areas that's different from the open ocean populations?

THEY AIN'T GOT NO MUSSELS!!!

Instead, they have ACORN BARNACLES!! (Balanus spp.)

(image from wallawalla.edu)

The immediate correlation seemed to be that this ecological/external effect (i.e., food type) was the reason why you get purple Pisaster ochraceus. It turns out that the mussel Mytilus contians carotenoid pigments, which are the same KIND of pigment that are responsible for the orange color in carrots!!
Harley et al. hypothesize that the mussels provide the pigment that yields the light orange/red color

(from MarineBio.net!)

and that those ochre stars deprived of mussels REVERT back to the bright PURPLE color!!! (note that mussels are absent in the pic below!)

They point out that the color still varies among individuals-some orange, some red/brown, and some in between. So, there might yet be an underlying genetic component to the variation in color.

They add anecdotal accounts that some orange adults turn purple when held for long periods under laboratory conditions and that small individuals of Pisaster are actually not fixed on a color. So SIZE and maturity may also be important factors.

But the authors save the best for last. They also speculate that those factors that affect color are apparently stable over relatively long ecological time scales.
In some places, such as the famous Pacific Grove, California (home to Ed "Doc" Ricketts and Cannery Row), they were able to determine that Pisaster size, color frequency and diet have not significantly changed in over HALF a Century!!!

So, this famous population of sea stars has not undergone any real changes in prey abundance for the last 60 years or so!

The Pisaster Post! Posterchild or Portent ??

(from MarineBio.net!)

This week, we're talking about the Pacific Northwest Intertidal!!

And what animal is more iconic to this area then Pisaster ochraceus (family Asteriidae)-the familiar intertidal Ochre Star found on rocky, mussel-laden substrates on from Alaska to California to Mexico. Some more basic information is here.Interest on this species has shifted over the years and seems to change based on some of the "big science" of the day. Yet another sign of how the humble starfish has incorporated itself into the fabric of the BIG scientific picture!

So, today some highlights of the importance of the ever-humble intertidal Pisaster ochraceus and how its study has varied over the years....

1. The Keystone Species Concept-Ecology's Posterchild. Probably one of the most lasting ideas from the 1960s and 1970s was the hypothesis developed by ecologist Robert T. Paine who identified Pisaster ochraceus as a keystone species (keystone shown below in grey).To quote Wikipedia:

A keystone species is a species that plays a critical role in maintaining the structure of an ecological community and whose impact on the community is greater than would be expected based on its relative abundance or total biomass

This keystone is a crucial block in an arch that keeps it from collapsing. This is analogous for Pisaster's influence on the mussels and the other invertebrates that exist in a rocky intertidal ecosystem.
The loss of the "keystone species" results in a drastic shift among these species....The idea has endured and while not embraced by everyone- remains a mainstay in basic ecology books. More details on this notion can be found here.

Pisaster along with its prey, the mussel Mytilus are almost ALWAYS the featured example... the POSTER child for the keysone concept-and for this reason, is probably even better known then the Atlantic Asterias!
This was (and continues to be) an important ecological notion during a time when the ecosystem and ecologists were in ascendance and ecology was a huge primary mainstay of biological research!

2. Pisaster as a Portent of Change?? The Canary in the Cage of Climate Change??
Probably one of the biggest, new research directions these days?

Understanding Climate Change and in turn...increased ocean temperature, which has a HUGE impact!

It affects ocean water chemistry. Water chemistry in turn can change everything from mineral absorption, feeding behavior, physiological systems to larval settlement. These in turn can have influence on MILLIONS of tiny larvae in the water. As well as the MANY adults those starfish grow into.

This translates into many people interested in the effects of increased temperature and heat relative to the ability of common species to adjust. Will Pisaster ochraceus take on a new status as a possible indicator species (i.e., canary in a coal mine) for climate change effects in marine systems?

Here is a survey of three recent studies (2008-2009) that have looked at how Pisaster holds up!

Elevated water temperature and carbon dioxide concentration increase P. ochraceus growth!

(Diagrammatic graph by Echinoblog Art Department!)

Rebecca Gooding, Christopher Harley and Emily Tang at the University of British Columbia published this study in the Proceedings of the National Academy of Sciences wherein they found that increases in temperature from 5 to 21 degrees C led to increases in feeding AND overall growth.

This bucked the predictions that the decreased carbon dioxide resulting from increased temperature would prevent animals that use calcium carbonate to form their skeletons (such as coral)!!

Solar radiation plays a role in P. ochraceus habitat selection

(Diagrammatic graph by Echinoblog Art Department!)

A 2008 paper by Jennifer Burnaford and Melissa Vasquez at the University of Puget Sound studied where P. ochraceus occupied habitat and their tolerance of Ultraviolet radiation.
The short version of this-the authors found that in artificial lab experimetns, P. ochraceus avoided ultraviolet and "photosynethetically active radiation" and observations of Pisaster in the intertidal found that 85% of them occurred in shaded habitat underwater where they were shown to preferentially avoid direct exposure to sunlight (see diagrammatic graph above!).

P. ochraceus avoids extreme body temperature by pumping its body full with cold sea water!!

(Diagrammatic graph by Echinoblog Art Department!)

Sylvain Pincebourde, Eric Sanford, and Brian Helmuth recently published this paper (2009). A popular account can be found here (and for shame to Live Science for misspelling "ocher").

Their paper details how Pisaster ochraceus was observed to increase the amount of colder water in their body cavity lowering their body temperature during the subsequent low tide in response to the temperature.

Sense it getting warm? don't like it? Just PUMP IT UP! with cold water! (see diagram above)

But climate change has a huge potential impact on animals that do this...to quote in their words:

When placed in a global change context, these results suggest that a continued increase in ocean temperature may compromise the ability of sea stars to avoid thermal stress during aerial exposure at low tide.

Has the humble Pisaster ochraceus gone from ecological poster child to a possible portent of climate change to come??? Time will tell....

Meet...The Farallons: ROCKY Intertidal Wilderness of San Francisco!!!!

So, one of my esteemed colleagues at the California Academy of Sciences-Dr. Rebecca Johnson Rodgers, who has worked with the Echinoblog while teaching at San Francisco State,is currently out on the Farallon Islands with the Rocky Shore Partnership monitoring various intertidal invertebrate critters. So, I wanted to give them some bloggy love:
Click here for their blog...
For those who are not familiar, the Farallon Islands are some remote islands, about 27 miles outside the Golden Gate Bridge (outside of San Francisco Bay).. Here is the Wikipedia page for the Farallons for more..

But the short version is, that they are remote islands that are protected as a wildlife refuge. The Farallons are great for birdwatching and have lots of great (hopefully still...) pristine intertidal reef habitat.

Plus, as a bunch of rocky islands out on the outskirts of San Francisco Bay, you get lots of this...



Along with many of the classic California invertebrate fauna..

Leptasterias "hexactis", shown here with brooding eggs!! This is part of the Leptasterias species complex which I have written about here and here
and, of course, the good ol' workhorse starfish Pisaster ochraceus, which I will be writing up in the blog later THIS WEEK!!!

and just because they're so dang beautiful...these mollusks too!!! This used to be called Tonicella lineata, but I think the name's been changed recently...
....and back in the Paleozoic when I took Intertidal Ecology, this thing was called Calliostoma, but I gots no idea what the kids are calling it these days!
GO check out the Rocky Shore Partnership BLOG and I'll be back in a few days with some PISASTEROUS starfishy goodness for all o' y'all!