[sci.aquaria] coral reefs, C02, food, and farming.

rosentha@sierra.Stanford.EDU (Peter A. Rosenthal) (12/01/90)

rosentha@sierra.Stanford.EDU (Peter A. Rosenthal) writes:
>>
>>	It is well known that healthy coral reefs are quite
>>effective at fixing carbon dioxide into calcium carbonate skelatons.
>>They are also remarkably productive ecosystems that support enormous 
>>diversity in an astoundingly nutrient poor environment.  I would
>>like to start some discussion on the possible importance 
>>of coral in fixing C02 from the atmosphere.

Ben Chase says:

>As for Peter's question, IMO I don't think reef-building corals can be
>effectively used to abate atmospheric CO2.  I think their ability to
>fix CO2 will be limited by calcium and other nutrients.  Also,
>reef-building corals are restricted to warm waters.  

>the simplest solution to reducing atmospheric CO2 is of course to stop
>putting CO2 into the atmosphere.  One quarter of all the CO2 generated
>by humans is generated within the USA.  Note that this is far larger
>than the percentage of humans that live in the USA.

I would like to follow up on this.
	I agree with Ben that reducing sources of C02 into the atmosphere
is the most important and simplest way to reduce any greenhouse effect related
climate changes.  I think there are some other imaginative things to
consider too.  I don't think Calcium limits reef growth in nature, though
it may deplete quickly in a closed aquarim.

	Coral reefs get most of their calcium  directly from disolved
calcium bicarbonate in the sea water.  There is a virtually inexhuastible
supply of calcium in the ocean in this context.  The whole reason I
started this thread was that I was struck by how little actually goes
into a coral reef other than solar energy, and calcium carbonate.  Sure
there must be some nitrogen and minor elements for building biomass,
but mainly the coral reefs get everything they need from the seawater, the
sun and the atmosphere.  Aquarists bend over backwards trying to remove
nutrients from their aquaria to help their corals grow.  The wet dry
filters, ozonizers, protein skimmers that occupy so much attention among
mini-reef keepers attests to this point.

	Coral reefs, including all the concomittant lifeforms such as 
fish, molluscs, worms, sponges, etc. could probably grow in any clean,
well illuminated tropical sea if they had a suitable substrate at the
right depth and were seeded with a wide enough diversity of life.

	Open deep tropical ocean is a relatively unproductive place.
There are not enough nutrients to grow much algae or zooplankton, so the
main inhabitants are relatively large pelagic creatures that feed off of
each other and ultimately from more productive areas such as coral reefs
or nutrient rich upwellings such as are found in the northern seas.

	If one could float large substrates out in the open ocean several
meters below the surface, and properly seed them, I would bet that
reefs would grow very well on them provided they were located in a
stable, well lit, clean place.  Coral occupies only a small area on
the planet presently;  I wonder how many square miles?  How difficult
would it be to double the area artificially? 

	Coral reef farms of this sort would also be a great sustainable
food source for humanity as well as the rest of the world.

eesnyder@boulder.Colorado.EDU (Eric E. Snyder) (12/03/90)

>rosentha@sierra.Stanford.EDU (Peter A. Rosenthal) writes:
>>>	It is well known that healthy coral reefs are quite
>>>effective at fixing carbon dioxide into calcium carbonate skelatons.

I am not sure that this is any better an idea than simply seeding the
ocean with iron to permit proliferation of photosynthetic algae.  I have
seen it written (maybe even in sci.bio!) that only a few super-tankers
full of iron salts (Fe(II) abd Fe(III) being the major growth limiting
ions in sea water (which is to say that the main reason the oceans aren't
full of algae is that there is insufficient iron)) would suffice to 
allow enough algae to grow to off-set the current increased CO2 flux.

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TTGATTGCTAAACACTGGGCGGCGAATCAGGGTTGGGATCTGAACAAAGACGGTCAGATTCAGTTCGTACTGCTG
Eric E. Snyder                            
Department of MCD Biology           What do I care; I'm wasting fingers
University of Colorado, Boulder     like I had them to spare.
Boulder, Colorado 80309-0347                                           --BE
LeuIleAlaLysHisTrpAlaAlaAsnGlnGlyTrpAspLeuAsnLysAspGlyGlnIleGlnPheValLeuLeu
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JAHAYES@MIAMIU.BITNET (Josh Hayes) (12/04/90)

Corals grow quite slowly in most cases (though members of two families,
the Acroporidae and the Pocilloporidae, tend to be ramose or branching
in colony structure and can sustain rapid rates of extension, like in
the neighborhood of 15 cm/year), usually 1 cm/yr or less. The amount of
CO2 taken up and then immobilized in skeleton is probably, therefore,
rather small, by comparison with the CO2 taken up by the zooxanthellae
(symbiotic algae), converted to energy-bearing compounds, and trans-
located to the coral tissues then used in respiration and re-released
to the water as CO2. The zooxanthellae might be really cranking along,
contributing as much as 70% of the daily requirement toward animal
respiration (Muscatine et al. 1981). Plants are MUCH better at taking
up CO2, but again, it is not immobilized for long at all. Still,
an increase in the size of even a temporary CO2 sink would be helpful.
 
I am a little concerned about the blithe assertion that calcium is
not limiting here; releasing Ca from CaHCO3 leaves free bicarbonate
ions floating about, which as you recall from your human physiology
class associates with free hydrogen ions to form carbonic acid, which
dissociates to water and CO2....thus regenerating CO2. I dunno how
seriously this process would bollix up the sinking of CO2 on the whole,
but it needs examining.
 
We now return you to your regular broadcast....
 
Muscatine, L., L.R. McCloskey and R.E. Marian. 1981. Estimating the
  daily contribution of carbon from zooxanthellae to coral animal
  respiration. _Limnol._ _Oceanogr._ 26(4): 601-611.
 
-------------------------------------------------
Josh Hayes, Zoology Department, Miami University, Oxford OH 45056
voice: 513-529-1679      fax: 513-529-6900
jahayes@miamiu.bitnet, or jahayes@miamiu.acs.muohio.edu
"I am the Supreme Being, you know; I'm not completely dim."

rosentha@sierra.STANFORD.EDU (rosentha) (12/04/90)

J Hayes had a point that calcium might be the limiting factor in
C02 fixation, and that C02 is released when Calcium carbonate is
precipitated.  This is true but a little misleading.  Calcium 
Bicarbonate has two bicarbonate ions.  When a reaction removes
a C02 from the disolved HC03- then usually a molecule of CaC03
precipitates out.  This is probably the reaction that coral
uses to build its skeleton.  I would like to know how much
of the corals photosynthesis goes into reef building and how
much goes into respiration.  This reef building activity
seems quite similar to what the freshwater gardeners
call biogenic decalcification, where plants absorb bicarbonates
from the water rather than dissolved C02, and precipitate calcium
carbonate all over the place.  This is not usually a good situatin
in a plant tank, and indicates too much light for the available C02.

	How slowly do reefs really grow?  If a one square kilometer
area grew a 1 cm layer of Calcium carbonate per year, then we would
be fixing 10^10 cc's of carbonate each year.  This probably weighs
on the order of 10^7 kilograms or 20 million pounds.  This is not
that small a number is it?  


		PEter Rosenthal

jackson@ttidca.TTI.COM (Dick Jackson) (12/05/90)

In article <18@sierra.STANFORD.EDU> rosentha@sierra.STANFORD.EDU (rosentha) writes:
>J Hayes had a point that calcium might be the limiting factor in
>C02 fixation, and that C02 is released when Calcium carbonate is

I think it was meant as a joke, but with an element of sense, where a
letter to the New Scientist magazine suggested that the best way to lock
up excess CO2 would be to breed some very large (somewhere around
10^10 -- I can't remember exactly) oysters.  Probably the letter writing
chappie rather fancied the idea of contributing to the disposal of the
oysters' insides.

Is it not true that when the earth was young and had a lot of CO2 and
all was happy because humans had not appeared, biomass used up a lot
of it (oil) and shellfish also (limestone).  Since we are undoing the one
mechanism (trees ->oil) it makes sense to fix it by helping the other one
along. But is there enough calcium?

Dick Jackson

jeff@grce.UUCP (Jeff Frank) (12/11/90)

In article <90337.112001JAHAYES@MIAMIU.BITNET> JAHAYES@MIAMIU.BITNET (Josh Hayes) writes:
> 
>I am a little concerned about the blithe assertion that calcium is
>not limiting here; releasing Ca from CaHCO3 leaves free bicarbonate
>ions floating about, which as you recall from your human physiology
>class associates with free hydrogen ions to form carbonic acid, which
>dissociates to water and CO2....thus regenerating CO2. I dunno how
>seriously this process would bollix up the sinking of CO2 on the whole,
>but it needs examining.

Your concern is well placed but you should take into account the effect
of pH.  This "regeneration" you refer to is a function of protons 
(hydrogen ions) present in solution.  At pH 8.3 (I think I remember
reading somewhere recently this is the average pH of oceans) there
are relatively few protons to "liberate" CO2 from HCO3-.

I have in front of me a graph entitled "The Relationship of Hydrogen
Ion Concentration to the Percentage of Total Carbon Dioxide in Each of
Its Forms in Water" (adapted from Emerson, R. and Green, L., 1938.)

It depicts pH from 4-12 along X-axis and per cent of total CO2 along
Y-axis.  There are 2 bell shaped curves.  One begining at pH 4,
percentage zero rising in sigmoid fashon to its asymptote at pH 8,
falling in sigmoid path to zero at pH 12.  This is the HC03- 
percentage of total CO2.  The other curve depicts the free CO2 and
CO3-- percentage of total CO2.  It of course begins at 100 per cent
CO2 at pH 4 and drops conversely to HCO3- curve.  At pH 6.5 there
is half CO2 anf half HCO3-.  At pH 8 we have 100% HCO3- so, there is
zero CO2.  Since free CO2 is no longer viable at higher pH, the
"CO2 or CO3--" curve now depicts percent CO3--.  At pH 10 there is
half HCO3- and half CO3--.  At pH 12 there is 0% HCO3- and 100%
CO3--.

This means that at typical ocean pH, any CO2 introduced will be
immediately converted to HC03-.  As pH would lower (as would happen
with tremendously high CO2 additions) the buffering effect would get
weaker and weaker, but it would take an awful lot of CO2 to do
the job.

cmccaff@urbana.mcd.mot.com (Chuck McCaffrey) (12/03/98)

In article <720@sierra.stanford.edu> rosentha@sierra.Stanford.EDU 
(Peter A. Rosenthal) writes:

<<Interesting speculations about coral reefs as a natural sink for
over-abundant CO2 deleted.>>

	   If one could float large substrates out in the open ocean several
   meters below the surface, and properly seed them, I would bet that
   reefs would grow very well on them provided they were located in a
   stable, well lit, clean place.  Coral occupies only a small area on
   the planet presently;  I wonder how many square miles?  How difficult
   would it be to double the area artificially? 

	   Coral reef farms of this sort would also be a great sustainable
   food source for humanity as well as the rest of the world.

____

Very interesting idea, one that had not occurred to me.  My questions are:

1) How large are the "large substrates"?

2) How do we make the "large substrates"?  What do we make them of?
Will their manufacture cause, in and of itself, a large release of 
CO2 or pollutants?

3) Will the installation disrupt anything that should not be disrupted?

Still, an idea worth considering, along with, naturally, decreasing
the amount of CO2 we cavalierly dump into the ecosphere.
--
  \Chuck McCaffrey cmccaff@urbana.mcd.mot.com 1101 E University Urbana IL 61801
   \    Flashing for the warriors whose strength is not to fight,    [my words]
    \   Flashing for the refugees on the unarmed road of flight,  [my opinions]
   / \   And for each and every underdog soldier in the night,
  /   \    And we gazed upon the chimes of freedom flashing.