CO2, light, temperature and nutrients...

[jeremai]

Environmental conditions are known to exert a strong control on the rate of coral calcification. Calcification increases with increasing light up to a limit and then saturates. Calcification increases with increasing temperature up to a thermal optimum at or 1-2°C below the normal peak summer temperature and then declines steeply with further increase in temperature. In laboratory studies, nutrient concentration of the experimental incubation water during growth also affects coral calcification. Enrichment of nitrate to levels of 5 to 20 M result in increased zooxanthallae density and photosynthesis, and decreased calcification. High ammonium enrichment produces similar results. The increase in zooxanthallae density and photosynthesis and decrease in calcification has led to the working hypothesis that nitrogen enrichment enhances the net growth of the zooxanthallae, which, in turn, limits the supply of DIC available to the animal host for calcification. The exception to this explanation is the study by Ferrier-Pages et al. [2001] who observed a 23% decrease in calcification in response to nitrate enrichment ( 2 M) but no change in zooxanthallae density or photosynthesis.

Section 1.1 in this article:

 

Effect of elevated pCO2 on photosynthesis and calcification of corals and interactions with seasonal change in temperature/irradiance and nutrient enrichment.

 

Parts of this are pecking at my brain a bit, but I'll wait till I read more of it (it's a doosie) before asking for specific comments from the gallery. Just wanted to get the topic started.

[Mr. Fosi]

Tagging along.

 

It is late and I will not have enough time to read it tonight, but I will get through it tomorrow and post some thoughts (if I have any ).

 

EDIT: I like seeing this kind of stuff (peer reviewed journal articles and relevant discussion) in advanced topics.

[MrAnderson]

Ok I finally read the thing. Thank god half was references.

 

On the one hand the bit about the atmospheric elevated CO2 affecting saturation kinetics of carbonate is kinda scary, but it's unclear if this is balanced by a greater availability of external carbon for fixation in metabolism. It's not clear what the chemical relationship between photosynthesis and calcification is.

 

I understand the idea of nutrient loading for cellular studies, but in this case they dose with ammonia, nitrates and phosphates specifically targeting photosynthesis. This makes for happy zooxanthellae, but what about the heterotrophic portion of coral metabolism? If you're targeting one portion of the symbiosis like this, it might be affecting the other partner negatively. Their control for this question demonstrates this, but they claim the 16% change is not significant. BUT long term effects of this manipulation aren't studied; i.e. the coral cells continually gearing up/spooling down production of metabolic components. They point out this nutrient feeding isn't to simulate natural eutrophic nutrient upwellings, but the manic nutrient loading/ablation seems to stress the corals, by their own data. Constant repeated stressing is begging for artifacts.

 

This is tough work, no doubt, because of so many interconnected variables. The whole thing seems destined for Heisenberg-style artifacts, even in a carefully considered and planned out model system like this.

 

Until they figure out a unified theory of photosynthesis/calcification to test they are flying blind in a way.

[Mr. Fosi]

Well, I finished that paper. Boy, what a bear.

 

They said many times that "the coral took up # of X" compound, but did I miss their control of other photosynthetic organisms? I saw that they scrubbed the thing for filamentous algae, but what about nitrifiers and encrusting algaes?

 

... in this case they dose with ammonia, nitrates and phosphates specifically targeting photosynthesis. This makes for happy zooxanthellae, but what about the heterotrophic portion of coral metabolism? If you're targeting one portion of the symbiosis like this, it might be affecting the other partner negatively.

 

Yeah, this is something that jumped out on me as well.

 

BUT long term effects of this manipulation aren't studied; i.e. the coral cells continually gearing up/spooling down production of metabolic components.

 

Right. Long-term effects seem to be their implied interest. I understand that studies have to be limited in scope or you lose a lot of control and ability to analyze data, but... I'm not sure what I could suggest to make the study better.

 

Their discussion of CO2 dissolution was kind of interesting and scary, but there are pleanty places for carbon to go before it causes Ca precipitation or combination into HCO3. What about the plethora of non-calcifying corals, kelps, macros, encrustings, and phytoplankton?

[MrAnderson]

Right. Long-term effects seem to be their implied interest. I understand that studies have to be limited in scope or you lose a lot of control and ability to analyze data, but... I'm not sure what I could suggest to make the study better.

 

Over the course of a couple weeks they keep dosing and ablating these nutrients to the test subjects, seemingly stressing them over the course of a very long experiment, is what I meant. To their credit they mention that the system is highly unnatural and to be regarded carefully, but they don't really elaborate on the artifacts their methods might introduce, long-term, but still within the time-frame of the experiment.

 

When they loaded nutrients they found photosynthetic carbon fixation went up with a concurrent decrease in calcification. Their conclusion is that it's because of competition over the same limited pool of intracellular DICs, but don't address the problem that stressing out the corals in their experimental system with repeated exposure to ammonia might contribute to lower calcification rates.

 

Their assumption is that both symbiotic partners are happy with ammonia around, and are functioning normally.

 

Maybe corals like ammonia and nitrates?

 

Their discussion of CO2 dissolution was kind of interesting and scary, but there are pleanty places for carbon to go before it causes Ca precipitation or combination into HCO3. What about the plethora of non-calcifying corals, kelps, macros, encrustings, and phytoplankton?

 

That's a good point. The ocean isn't a closed system, and other more efficient photosynthetic organisms might make quicker use of DICs and functionally lower concentrations before zooxanhellae have to deal with them. But if they do that means higher rates of photosynthetic growth... algae blooms, barring other rate-limiting factors (they do exist, though)...

 

But the idea they discuss of a global oceanic pH drop is feasible, theoretically. But the ocean also has a huge supply of carbonate buffer to equilibrate this... Oh well we'll just have to see, won't we!

[MrAnderson]

Another thing which is interesting is the positive differential of CO2 between Kanehoe Bay and the atmosphere; the seawater concentrations are higher than atmospheric concentrations and thus the flow of CO2 is actually from sea to atmosphere, not the other way around, at least in this locale, leading one to infer that it's the sea adding CO2 to the atmosphere, not the other way around!

 

 

 

Also, the experimental setup in Table III looks sketchy to me. When they compared nutrient-loaded with non-nutrient loaded corals and their response to higher CO2, they used different concentrations of CO2:

 

nutrient loaded CO2 (x over ambient): 1.0, 1.4, 1.9, 0.6

non nutrient loaded CO2: 1.0, 1.3, 2.0

 

They mention the response to CO2 is linear, but why mathematically normalize the experimental values based on a curve, instead of just keeping CO2 concentrations the same between experiments? I would think normalizing the [CO2] would be better design.

 

On that note, the raw data is pretty heavily processed. Some of the individual experiments show the opposite, or negative result. Only after a lot of statistics do they get barely significant numbers in some cases.

 

I know that this is extremely difficult work, but it looks like they confound the data more than they should in certain experiments. The CO2 concentrations I noted above are a good example, and I would think that could have been avoided.

[jeremai]

Maybe corals like ammonia and nitrates?

I think that was the thing that stuck out with me. I've heard this before, when I used to spend money on SCUBA gear and not fish tanks. There are a lot of near-shore habitats where ammonia and nitrates are not at zero all the time. It's interesting to think of how this could relate to the hobby in a few more years.

But the idea they discuss of a global oceanic pH drop is feasible, theoretically. But the ocean also has a huge supply of carbonate buffer to equilibrate this... Oh well we'll just have to see, won't we!

Didn't they mention that the pH drop was occuring in the uppermost parts of the ocean? Or was that a different article?

[MrAnderson]

Didn't they mention that the pH drop was occuring in the uppermost parts of the ocean? Or was that a different article?

 

They mentioned it as a theoretical eventuality, no references, last sentence of conclusions. Sorry if I wrote "discussed".

 

BTW sorry for lapsing into journal club mode and picking the paper apart... I'm no marine biologist, but certain experimental design principles are universal. I'm sure they had plenty of practical and logistical limitations to deal with and that probably explains some of it. Part of my intention was to introduce some doubt about their conclusions, particularly the extrapolation in the last figure, which I think is a bit of a non sequitir based on their data alone. In other words: don't worry yet.

 

On the other hand it was an informative read. Please post more stuff like this if you come across it... there's always stuff to learn. Overall, the ideas being examined are very very interesting.

 

Hey tiny, you're pretty up on stuff like this, how come you don't post interesting stuff like this?

[MrAnderson]

Pacific Ocean getting warmer, more acidic

[Mr. Fosi]

Pacific Ocean getting warmer, more acidic

 

That article was bare of methods.

 

I wonder how, when, and where you took their pH readings. What depths, what areas, over what timespan, you know?

[MrAnderson]

That article was bare of methods.

 

I wonder how, when, and where you took their pH readings. What depths, what areas, over what timespan, you know?

 

it was AP not Nature.

 

Just thought it was relevant. If I get around to it I can try to find the primary source..