[Coral-List] From a Keys farmer
kleypas at ucar.edu
Thu Apr 5 12:43:38 EDT 2007
I think your observations and questions about CCA growth rates are very
insightful and worth further research. Mark made the point that
carbonate saturation state is [partially] controlled by temperature and
pCO2, which is correct, but these are not the only variables that
control saturation state. Nor are temperature and saturation state the
only variables that control calcification rate.
First, from what I know, there is little information on what controls
coralline algal growth and calcification, and it would be great to
supplement your long-term observations with good environmental data from
your culture site. I can imagine that there are several possible
environmental changes associated with your autumn "bloom" of CCA, such
as a decrease in temperature, a change in light regime, a change in
calcium carbonate saturation state (which is seasonally affected by
several factors such as alkalinity and temperature), nutrient levels, or
simply a combination of variables that triggers the algae to grow.
While there is good evidence that future changes in carbonate chemistry
will increasingly be a factor in calcification rates (and dissolution
rates!), given the complexity of these systems, I would hesitate to
point solely to carbonate chemistry as the trigger for your bloom.
For example, as temperature drops (and all other variables stay the
same), the saturation state would actually decrease. But if there is a
macroalgal bloom going on at the same time, then it is possible that the
photosynthetic CO2 drawdown would lead to an increase in saturation state.
Second, the few data on how saturation state might control coralline
algae calcification rates are confusing. There is some evidence that
saturation state controls calcification rate (e.g. Chris Langdon's work
in the Biosphere 2 mesocosm, which was dominated by coralline algae).
There is other evidence that coralline algae recruitment declines with
decreasing saturation state. But ongoing experiments (presentation by
Sophie Martin and JP Gattuso at the ASLO meeting) seem to paint a more
complicated picture, in which as you suggest, there is an interaction
between both saturation state AND temperature.
You make a great point: "It would be interesting to see some large
scale/long term field research on this topic as we struggle with the
questions surrounding globally rising temperatures and CO2." Perhaps
your CCA site is a good candidate for this kind of monitoring! To shed
light on which factors are stimulating the CCA blooms, this would
require long-term monitoring of at least temperature, salinity, light,
saturation state and nutrients. It would also be great if you could
measure *true* calcification rates rather than extension rates.
Unfortunately, both carbonate chemistry and calcification rates are
challenging measurements, and the "Impacts of Ocean Acidification on Coral
Reefs and Other Marine Calcifiers - Guide for Future Research" that Mark
and Chuck mentioned provides a summary of those challenges.
apologies for the lengthy message,
terrasubaqua at peoplepc.com wrote:
> I would add a personal observation to the global warming discussion based on ten years (~4 one week visits /yr) at the same spot off Plantation Key.
> There is a fundamental chemistry link between the solubility of calcium salts and water temperature, and we can see the local biochemical link to crustose coralline algae (CCA) growth rate at work each Fall. During this seasonal change, our aquaculture substrate coquina rock gathers a nice coating of CCA over a period of several weeks, commencing just as the water temperature drops. The CCA appears to cover substrate much more rapidly in the Fall months than at any other time of year, it's a very colorful phenomenon and one we watch closely because CCA means added value to our live rock products. We see that, with other variables held to a (roughly) narrow range, the rate of CCA coverage growth seems largely related to the degree of saturation of the calcium salts in the seawater.
> This may have global ramifications, with global water temperatures rising and considering the significance of calcium carbonate deposition to the global sequestration of carbon dioxide. I wonder how rising water temperatures affect the global deposition of calcium carbonate? Though we might assume from controlled experiments it would be detrimental, some biological factors such as faster overall growth, reproduction rate, and/or coverage of CCA in warmer water, or over water temperature changes spanning particular ranges, might control natural feedback mechanism(s) assisting CCA (and possibly other calcium carbonate 'bio-consumers'?) in global- scale sequestration. Even though CCA seems to grow much more slowly (if at all) in mid-winter at our site, the warmer global water temperatures we encounter may also enhance reproduction or otherwise benefit overall growth over the span of a year. It would be interesting to see some large scale/long term field research on this topic as
> we struggle with the questions surrounding globally rising temperatures and CO2.
> Tim Birthisel
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> Coral-List at coral.aoml.noaa.gov
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kleypas at ucar.edu
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