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#126
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Greetings All !
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The evolution of aquarium protein skimmers during the last 20 years has been nothing less than extraordinary. It seems to me that (... if we're willing to plunk down the cash ...) there are more than a few brands which are more than capable of "stripping" as much POM & bacterioplankton from the water column as we might safely generate. Adjusting the hours of skimmer operation presents a reasonable opportunity for "gross" export control. It seems to me that there are more than a few folks playing around with this husbandry tactic for a while. The other opportunity has to do with bacteriplanktonic systems which incorporate some form of culture vessel. For this kind of configuration ... the characteristics & volume of media, the flow rate through the vessel, rate of violent disruption of the media, and on-off cycling of the pump operating the vessel are all indirect opportunities to control export (by influencing "production"). JMO
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Mesocosm Last edited by mesocosm; 08/20/2007 at 11:02 PM. |
#127
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I for one must say that this has to be the best thread I have read on RC in a long time. However, most of it is over my head but I can see the big points. Any opinion on why the alk has to be strictly maintained on some of the bacteriaplankton systems?(6-7.5 dkh)
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"He is your friend, your partner, your defender, your dog. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion" |
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I read one person's opinion on this on the Zeovit forum recently. He said that in the ultra low nutrient environments, zooxanthella in the coral is reduced (this creates the nice colors); but with those reduced and their associated food source, corals can't sustain new growth at the accelerated rates that higher alkalinity promotes. Instead, they tend to burn out/die. That is one person's theory in non-scientific terms but it makes sense to me.
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#129
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Canarygirl, there are a lot of theories... the answer is unknown. jake, the reason is that many experience burnt tips when higher than NSW levels are kept. Unfortunately, it's not the root cause. I've experienced it a few times....
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#130
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Second, increased alkalinity (which will increase the DIC) will reduce carbon limitation of the zoox. (though they probably aren't C-limited in most corals at fastish current speeds) and therefore increased alkalinity would increase the availability of photosynthate to both the corals and zoox., increasing their energy budgets. However, that is only true if the zoox. are C-limited, which they may be in relatively slow water motion, but probably are not on real reefs, or if they get sufficient water flow in reef tanks. Third, calcification and photosynthesis are correlated, but not necessarily coupled (in fact, they are easy to decouple). Increased alkalinity increased the supply of DIC to calcification. Since calcification in most corals is likely C-limited this will increase calcification. If the coral calcification exceeds the rate of growth of the zoox. you'll get lighter colored tissue in the areas of growth. For some corals, this is the typical growth form. For instance, Acropora have zoox.-free axial coralites, yet this is the fastest growing part of the colony. There has to be some good regulation of the population and distribution of zoox. in the corals though, because a similar pattern is maintained even with widely variant rates of calcification. Corals in shallow water and corals in deep water maintain similar populations of zoox. even though they might be growing at very different rates. More than anything though, I think it is worth considering what happens to corals out in nature that we know are living in low-nutrient water and in a relatively healthy setting. As I mention above, increased alkalinity means increased calcification (at least for the corals studied thus far). Chris
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FSM ~ Touched by His noodly appendage ~ |
#131
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Geochemical Perspectives on Coral Mineralization Anne L. Cohen & Ted A. McConnaughey http://www.whoi.edu/science/GG/peopl...ralization.pdf HTH
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"Natural does not imply ideal; only acceptable or tolerable." Photos of my "Blau Arborescent Dschungel Riff" via the red house. |
#132
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Assuming the article is correct (I am not questioning it) there are some real one sentence zingers in there, particularly from page 28 on.
You could take some of those single sentences and spend years following up. |
#133
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Greetings All !
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From the article ... Quote:
... you're not hallucinating ... BTW ... read the section previous to this quote (page 30) and you'll see the potential for an increased electrochemical gradient in the membrane to attract stuff like ... NH4 and Fe. I dug the Cohen & McConnaughey one up because of a post by JWRE (... in another cyberspace far, far away). He reported that a group of German reefkeepers have been introducing CO2 in an effort to lower pH because they believe their corals (presumably SPS, but it was unspecified) demonstrate better nutrient uptake with the pH drop. Those crazy Germans. You've got to love 'em ... Cohen & McConnaughey also wrote this ... Quote:
Photosynthesis and Calcification at Cellular, Organismal and Community Levels in Coral Reefs: A Review on Interactions and Control by Carbonate Chemistry JEAN-PIERRE GATTUSO, DENIS ALLEMAND and MICHEL FRANKIGNOULLE American Zoologist 1999 39(1):160-183; doi:10.1093/icb/39.1.160 Full Article http://intl-icb.oxfordjournals.org/c...t/39/1/160.pdf This article presents stuff like this ... Quote:
And this ... Quote:
JMO
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Mesocosm |
#134
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Greetings All !
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JMO
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Mesocosm |
#135
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#136
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The McConnaughey and Whelan hypothesis (which Cohen and McConnaughey follows up on) of calcification enhancing photosynthesis is contentious, to say the least. It seems pretty likely that calcification (if calcifcation produces protons, which it likely does, although that is a whole set of assumptions...) could aide photosynthesis, but ONLY if photosynthesis is C-limited in corals. At reasonable current speeds, zoox. in corals seem saturated at concentrations somewhat below NSW levels, so calcification likely is not significantly affecting photosynthesis in corals (neither helping nor hindering). This seems especially likely considering that it is easy to decouple the processes. Add nutrients and photosynthesis will go up while calcification will go down AT NSW LEVELS OF C. If you raise the DIC increased nutrients can actually increase both photosynthesis AND calcification.
Also, I think the argument that corals calcify to increase nutrient uptake for their zoox. is incredibly weak. The primary limitation on nutrient uptake by corals and other benthic reef denizons is the rate of mass transfer from the water column. This is controlled primarily by the rate of water flow over/around the organisms, not by electrostatic interactions. If there are German aquarists that are dropping the pH of their tanks in an effort to increase nutrient uptake and calcification...they would be best to read some more of the primary literature on the subjects. A higher pH and another water pump would likely serve them much better (as a side note, I've seen some surprising responses to altered sea water chemistry in some of my work lately...) The best supported model for the effect of nutrients on calcification is C-limitation of calcification due to increased C-fixation by the zoox. While photosynthesis CAN increase calcification, the two can be decoupled easily as well. Calcification likely doesn't impact photosynthesis much. Light-enhanced calcification is well-supported, while calcification-enhanced photosynthesis has been at least partially refuted (all with respect to corals, of course). Quote:
Chris
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FSM ~ Touched by His noodly appendage ~ |
#137
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Greetings All !
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... not by a long shot. Quote:
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Is there really any question about this? JMO
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Mesocosm |
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Greetings All !
Before I post another word ... you're a pleasure to talk with Chris. Many have commented on the quality of this thread, and your contributions are a large part of it. Nicely done, everyone ... many thanks for all the wonderful enrichment opportunities that you have provided. Quote:
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Old belief systems die hard, don't they? ... Quote:
Here's one for you ... do you think that what folks are reporting is a "chemical toxicity" phenomena, or, a "bleaching" phenomena? I come down on the "bleaching" side of the fence ... hence "photoacclimation". From a different angle ... am I reading you wrong when I infer that you think it's a "toxicity" thing ("... it is an indirect and unfortunate side effect using whatever it is those folks are using in their systems")? If so, we have something else to discuss. I view the ease of remediation as a compelling demonstration against "toxicity". Quote:
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JMO
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Mesocosm |
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Greetings All !
Yikes ... I really do get way too excited about this stuff. If it's okay with everyone, let me try this again. Quote:
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Folks who have experienced "issues" report that once their alkalinity is restored to the 6.5-8.0 dKH range ... the "issues" disappear. I view this as more than compelling. I consider this to be definitive. "Photoacclimation" strikes me as a fairly reasonable vocabulary choice to assign to this dynamic, but I'm open to alternative suggestions. Even so, I concede that there is much room for informed perspectives to disagree about this. Quote:
The Physiological Mechanisms of Acclimatization in Tropical Reef Corals RUTH D. GATES and PETER J. EDMUNDS American Zoologist 1999 39(1):30-43; doi:10.1093/icb/39.1.30 Full Article http://intl-icb.oxfordjournals.org/cgi/reprint/39/1/30 Some extracts from the article ... Quote:
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"... there are strong anecdotal observations that corals with high growth rates have the tendency to undergo rapid bleaching (Suharsono and Brown, 1990; Jokiel and Coles, 1990; Glynn, 1993; Hoegh-Guldberg and Salvat, 1995), ..." Sounds a lot like what folks are reporting when they mismanage their alkalinity outside the 6.5-8.0 dKH range ... doesn't it? JMO
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Mesocosm |
#140
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But Why?
(Those of you with, or experienced with, kids will completely understand the context, meaning and inherent humor of those two words and will currently be rolling on the floor laughing. There is nothing like that split second of thinking you have explained life to your child only to have those two words flung back at you. To mesocosm, my apologies for the humor. It is purely a reflection of my ignorance and, well, maybe the headache you just inflicted upon me.) |
#141
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Thank you. |
#142
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Greetings All !
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From another ... are there any intracellular metabolic pathways in the zooxanthellae-host relationship which might be disrupted by HCO3, pCO2, microbial leakage, and/or nutrient uptake shifts (both + and -) ... or ... by changes in either electrochemical gradients, and/or osmoregulation (in general)? My answer to the last question is yes ... hence photoacclimation. For the record, I sit ready to concede to a better explanation. I have no personal investment or entanglement with this topic (... other than the absurd willingness to address it in the first place ...), nor have I asserted any claim of superiority of my perspective over another (... nor will I. Speculations about what's going on with the metabolism of corals are indeed contentious, as was previously pointed out). Everyone should feel free to dismiss my opinion at their leisure. Last bit ... we're not suggesting that what's being reported is a straight-up, single variable bicarbonate water chemistry event, are we? JMO ... your mileage will vary.
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Mesocosm |
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My-oh-my this whole thing is getting a bit thick isn't it....
On the whole McConnaughey hypothesis of calcification enhancing photosynthesis in corals (either by producing protons and increasing availability of CO2/HCO3- or increasing nutrient uptake), I just don't buy it. The experiments that have been done really don't seem to support the hypotheses. Ted McConnaughey is a great scientist and these hypotheses (first proposed some 10 years ago now) are good, solid and testable hypotheses and reasonable based on knowledge at the time, but in the last decade I just have not seen support that these factors are really very important. Sure, I can believe that protons produced by calcification (which assumes corals are using HCO3- or CO2 as the source of C) could aide photosynthesis, but to such a small degree that it probably doesn't matter. But again, if the zoox. are saturated with C at NSW levels (and reasonable water flow) then it really doesn't matter. The physiological data is inconsistent, the stoichiometry data is inconsistent and direct tests of the hypothesis appear inconsistent. It is/was a good idea, but I just don't see support for it. While this hypothesis seems more believable for algae and plants, I still have reservations about it. Terrestrial plants may well calcify accidentally in an effort to get nutrients. Aquatic plants *might* to the same, but it almost seems just a consequence of their physiology, nothing "intended" or mediated. When we start looking at calcifying marine algae I become less convinced that they are calcifying to affect CO2/HCO3- or nutrient availability and think that other reasons to calcify are more likely (e.g., physical defense). Quote:
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Let me take a closer look at the Gates and Edmunds paper... As for Tom Goreau Jr.'s comments: I would take them with a grain of salt--a large grain, actually Chris
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FSM ~ Touched by His noodly appendage ~ |
#144
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Canarygirl ... PMs are waiting for you. BTW, for anyone who was wondering ... Parsimony: In science, parsimony is to prefer least complicated explanation for an observation. This is generally regarded as good when judging hypotheses. Ockham's Razor also states this idea; More logical to accept a hypothesis that depends on a small number of processes rather than based on a large number of independant processes.
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Mesocosm |
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Greetings All !
Not to physically assault a dying equine, but I wanted to make one last comment. There are many competing models for what's going on, and if you want to see one of the better summaries of the competing topics and rersearch data ... read the discussion section of the following article. Imbalanced coral growth between organic tissue and carbonate skeleton caused by nutrient enrichment Tanaka, Miyajima, Koike, Hayashibara & Ogawa Limnol. Oceanogr., 52(3), 2007, 11391146 Full Article http://www.aslo.org/lo/toc/vol_52/issue_3/1139.pdf A few extracts ... Quote:
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JMO ... HTH ... out.
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Mesocosm |
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At the end of the day, or in this case the thread, it seems we really have a good handle on the biology and chemistry. I would like to see a similar thread on debating practical application of what we have discussed. Or maybe, and this would be another novel first for this forum, a thread where a collective practical model is built. It would be interesting to see how political that would get. I have a feeling it would not be as open as this thread was.
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