Maybe its the HEAT and not the acidity? A study of how Climate Change Affects Echinoderms!

(from SaSpotato on Flickr!)

So, there was big climate change news on the BBC website with a headline of "Sea urchins tolerate acid water" yesterday. An interesting article that showed the effects of carbon dioxide-rich water Atlantic shallow water sea urchin, Psammechinus miliaris to quote:

Whilst the scientists found no adverse effects on larval development or soft tissue production in the present study, they did observe a significant decrease in the amount of calcium carbonate that the organisms produced, resulting in smaller and thinner skeletons.

I should note that I haven't seen or had a chance to read the BBC paper as yet.. but a discussion on this topic with my colleague Dr. Allison Gong of UCSC (and who provided some Pycnopodia pix) reminded me of a paper I had seen awhile back.

Dr. Maria Byrne and her colleagues in Southern Australia published this 2009 paper with a telling title " Temperature, but not PH, comrpomises sea urchin fertilization and early development under near-future climate change scenarios".

I have previously written about how climate change may affect intertidal invertebrates here (effects on Pisaster and such)..

Byrne and colleagues studied the ecologically important sea urchin Heliocidaris erythrogramma which occurs widely throughout temperate-water Australia.

(from SaSpotato on Flickr!)

So, climate change's biggest impacts will most likely be in terms of sea-surface warming and ocean acidification. Good introductory articles on Wikipedia to global warming are here and for ocean acidification, here (short version: increased carbon dioxide creates more acidic ocean water) .

(this image from the BBC)

Echinoderms are composed of an internal calcium carbonate skeleton that is made up of millions of tiny pieces that are all infused with tissue.

As a consequence, echinoderms are one of the organisms likely to be affected by climate change because their skeletons are most likely be affected by the animal's uptake of calcium carbonate. Acidic (or warmer) water can dissolve/change/alter the chemical nature of calcium carbonate (aka chalk, limestone, etc.),

Byrne and her colleagues ran experiments that simulated future conditions of increased sea surface temperature AND an increasingly acidic ocean (i.e., a higher pH).

But rather than focus on adults, their efforts were directed at different life stages of Heliocidaris.
Namely, their larvae and the fertilized eggs.
This is actually one of the MOST important aspects of understanding the biology and evolution of marine animals. Like almost ANY animal, their "baby" stages are influenced and/or changed by the environment.

Larvae are also often WIDESPREAD. The little floating eggs and "babies" are found all throughout the water column and can be changed/affected by environment in ways that the adults can't be...
So, Byrne and her colleagues ran experiments where they changed the temperature and acidity during rearing conditions of fertilized/developing eggs of Heliocidaris.

They compared experiments versus a "control" standard was set at 20 degrees C (which is 68 degrees F) (with a PH of 8.2)

They varied environmental conditions up to 24 degrees C and 26 degrees C.

There were two experimental conditions outlining +4 and +6 degrees over the "control" temperature.

Their results are summarized in their Figure 1 below:
The top graph represents % of eggs that underwent fertilization
The middle graph represents % of normal cleaving embryos as temps increase from left to right.
The bottom represents % of normal gastrulation as temps increase from left to right.
Bar color represents the pH: black-8.2, dark grey-7.9, light grey-7.8, white-7.6 (so becoming MORE acidic from left to right)

What's Happening?
-The % of normal cell cleavage AND gastrulation (these are critical stages of cell development) were significantly LOWER. (dropping from the 65% that developed normally to LESS than 20% that developed normally!) at the warmest temperatures!
Basically, higher temperature created a BIG Developmental FAIL!!! Regardless of the pH (i.e., the acidity). Temperatures may affect various physiological processes that affect the development of the egg resulting in developmental failure!

How does this compare with other urchins?
Byrne et al. compared these results with the temperature and pH tolerances of other species and found that for five other species most of the known tolerances are only affected by a pH of LESS than 7.4 (the lowest they reached in the experiment was a pH of 7.6).

(thanks to Wikipedia for the pH scale!)

Normal seawater has a pH of about 8 (8.2 was measured for the sea urchins), and distilled water is about a pH of 7. Hydrochloric acid, what we use to digest food, is a pH of about 1.

Only the WORST CASE of ocean acidity would begin to seriously and fatally affect fertilization and development of baby sea urchins.

But it turns out that acidity on its own is a mixed bag for sea urchins (and probably other echinoderms)...

-on one hand, many sea urchins are quite tolerant to low pH (i.e., acidic conditions) owing to the relative acidity associated with fertilization. Sea urchin sperm actually has a pH of about 7.6!!

Indeed..some studies (such as this one by Wood et al. ) have shown that some echinoderms, such as brittle stars will actually show increased growth under acidic conditons!

(image from EPOCA Arctic Campaign 2009)

-BUT on the other hand, decreased pH may have a negative effect on larval calcification i.e, the ability to use calcium carbonate to develop their endoskeletons after sea urchins undergo early development. Animals could be weaker or have weaker "bones" as adults.

In the here and now- temperature is an important consideration!
Projections for eastern Australia indicate a surface sea temperature warming of UP TO 2 to 4 degrees C in the summer off the coast of New South Wales. Resulting in water temperatures of UP to and above 26 degrees C-Close to the temps indicated in their experiments!

And all this IN ADDITION to whatever possible stress may be caused by acidification!

So, while reports such as the one reported by the BBC are important, perhaps temperature will be the more important consideration in future studies???

Increased temperature appears to be one of the most important factors impacting many facets of the biology of adult echinoderms (and indeed-many other marine invertebrates) , including distribution, feeding, behavior, reproduction...but most importantly, the development and healthy survival of fertilized eggs and juveniles.

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....

Antarctic Brittle Stars Can't STAND the HEAT! Really. They can't!

(from EOL)

Today, a sobering paper I discovered regarding the thermal tolerance (i.e., how much of a temperature change can be tolerated) of the common Antarctic brittle star Ophionotus victoriae!

This post focuses on a study of the large and commonly encountered Antarctic brittle star Ophionotus victoriae (Family Ophiuridae) by Lloyd S. Peck, Alison Massey, Michael Thorne, and Melody Clark at the British Antarctic Survey, published this year (2009) in Polar Biology 32: 399-402.

The authors tested the ability of Ophionotus to respond to temperature changes over a discrete time period. They tested and compared two test groups, by increasing the temperatures of two test groups of brittle stars in two different tanks, one at a +2 °C and one at a +3°C (over their ambient temperature 0.4 degrees C) to see how long they would survive.

(from the Underwater Field Guide to Ross Island & McMurdo Sound)

Their results?

NONE of the animals were able to acclimate.

Their experiments showed that survival at +2 degrees C was about double that of the +3 degrees C batch. The threshold for this species is REALLY narrow. They can apparently handle ONLY a increase of +0.5 (from 0.4) degree C without any mortalities. To quote the authors:

"This is possibly the poorest acclimation ability of any species on record"

To spell this out: These brittle stars can't stand temperature change. They can tolerate a water temperature change of ONLY about 0.1 degree. If exposed to long-term temperature increase all of their body processes start to fail, the same way you would if you were left in the middle of a 90 degree day in the middle of the desert

How did this compare with other Antarctic megafauna?

Fish were the hands-down winners. They could apparently survive an increase of +4 degrees for periods in excess of 16 WEEKS!!

(Picture from the Alfred Wegener Institut for Polar and Marine Research)

The Antarctic Odontaster validus was able to withstand a heightened temperature of +6 deg. C !!(although time was not listed)

(from the Underwater Field Guide to Ross Island & McMurdo Sound)

So, the implications of this study are obvious (Can you say GLOBAL WARMING?).

Its not clear why or HOW some species are more temperature resistant then others but it seems likely that they are dependent on the individual TAXON (i.e., genus, species, whatever).

And while experiments like this should not be considered the final word, it does give some kind of barometer of capable these different species might be when facing a massive temperature change over a long period.
Some taxa will be able to adapt to temperature changes better then others. Various estimates have placed a rise of +2 deg. C over the next 100 years which is a rate FASTER then anything seen over the past million years or on record over the last glacial cycle.

Brittle stars are a substantial part of the bottom biomass in Antarctica (and in the deep-sea). They live on and in sponges and along the bottoms. They feed on and are likely food for many species.

Gradual temperature change can affect the effectiveness of feeding, reproduction, the ecology and food webs between these species will be substantially affected. You're talking about potentially a huge cascade collapse of the primarily invertebrate ecosystem in this area.

You want delicate Antarctic animals in the balance? Forget the Penguin. Forget the Fish.

Mind the brittle stars.

Will Starfish Benefit from Global Warming???

From Mongabay.com....

Based on studies by Rebecca A. Gooding, Christopher D. G. Harley, and Emily Tang at the University of British Columbia in Vancouver in a study to be published in PNAS next week....
(Rebecca A. Gooding, Christopher D. G. Harley, and Emily Tang. Elevated water temperature and carbon dioxide concentration increase the growth of a keystone echinoderm. PNAS Early Edition May 25, 2009)

To quote directly from their interview on Mongabay:

Climate change is expected to cause widespread disruptions to ecosystems and their resident species. Some creatures will go extinct, others will expand their ranges and thrive.

A new study identifies starfish as one of the possible winners from rising ocean temperatures and carbon dioxide concentrations.

Rearing Pisaster ochraceus , a species of sea star, under varying conditions, Rebecca Gooding, Christopher Harley, and Emily Tang of the University of British Columbia in Vancouver found that increased temperature and acidity will significantly boost the echinoderm's growth rate, more than offsetting the negative effects of reduced availability of calcium carbonate, an important structural building block for many marine invertebrates. The results contrast with other research which has shown a negative correlation between increased ocean acidity and growth rates of calcifying species.

"Our findings demonstrate that increased [CO2] will not have direct negative effects on all marine invertebrates, suggesting that predictions of biotic responses to climate change should consider how different types of organisms will respond to changing climatic variables," the authors write. "Some ecologically important species... may directly benefit from acidification."

Go to Mangabay for the full story....

(Wow....I wonder if this makes my job prospects any better?)