[34cygni]

Originally Posted by bertoni

Just to avoid possible confusion in the photosynthesis equation you gave, CH2O is formaldehyde, but it's a simple carbohydrate that works for a general explanation, but I am not sure that's what photosynthesis typically generates.

Note that the equation I gave is identical to the one at the beginning of the article you linked to. It's the standard simplified representation of photosynthesis, which is why I said CH2O represents sugar.

This is another way to write the equation for photosynthesis:

6 CO2 + 6 H2O ----> C6H12O6 + 6 O2

The product is glucose, the most common plant sugar. Divide everything by 6 and you get:

CO2 + H2O ----> CH2O + O2

Originally Posted by bertoni

Dinoflagellates generally don't affect the alkalinity appreciably because they don't calcify in most case, as you stated.

Dinos doing weird things to alk is a persistent, albeit minor, theme in this thread. DNA first mentioned it in post #1:

06/24/2013, 01:55 PM #1
DNA

Ca, Alk, Mg, Nitrates.
My tank has both had periods of low alkalinity and low calcium and at that time I though that had something to do with it, but having perfect parameters does not make dinos grow any less.

Photosynthesis normally tends to raise alk because it consumes CO2, which when drawn down will cause HCO3- to dissociate into CO2 and hydroxide. That's why the persistently low alk and Ca levels reported by DNA and others demand an explanation -- like I said, this has been at the back of my mind for a while...

Originally Posted by bertoni

They will consume a bit temporarily if they take up carbonate or bicarbonate as a carbon source, but the alkalinity is released after the carbon is taken.

http://reefkeeping.com/issues/2006-10/rhf/index.php#6

I don't see where that link provides evidence that marine primary producers consume alk when they're CO2 limited and running on bicarb -- in fact, the link you provided lands on a description of how bicarbonate is broken down and hydroxide generated outside the cell so that the resulting CO2 can be consumed... Perhaps you meant to link to Direct Uptake, as those reactions take place inside the cell, though again they indicate that hydroxide is being generated, not consumed. In any event, the reaction diagrams given for the Carbonic Anhydrase and Direct Uptake pathways are essentially identical, and both are consistent with this:

Originally Posted by 34cygni

Trouble is, the H+ required for this normally comes from H2O or HCO3- which leads to surplus OH- and CO3- and rising pH.

Just add water at the beginning to balance the reactions, and tack on photosynthesis at the end...
HCO3- + H2O ----> H2CO3 + OH- ----> CO2 + H2O + OH- ----> CH2O + O2 + OH-

Subtract the OH- common to each step...
HCO3- + H+ ----> H2CO3 ----> CO2 + H2O ----> CH2O + O2

Skip the intermediate steps and you get the simplified equation I originally gave...

Originally Posted by 34cygni

dinos aren't calcifying organisms, which means that they must be escaping CO2 limitation by using bicarbonate for photosynthesis:

H+ + HCO3- ----> CH2O + O2

But this was interesting:

Originally Posted by Randy Holmes-Farley in 'Photosynthesis and the Reef Aquarium'

Three marine bloom-forming (red tide) dinoflagellates, Prorocentrum minimum, Heterocapsa triquetra and Ceratium lineatum, have been shown to take up bicarbonate directly. They show little carbonic anhydrase activity, yet bicarbonate accounts for approximately 80% of the carbon dioxide they use in photosynthesis. It is believed that these dinoflagellates are not carbon limited in photosynthesis due to their efficient direct bicarbonate uptake mechanisms.

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Originally Posted by taricha

file this under theories that connect dots.

You rock. I missed this completely.

Originally Posted by taricha

on a separate note -
I turned off my skimmer 3 days ago, and I've looked through the microscope for hours and taken samples from all over my system: water column, deep dino territory, on the margins, healthy sand, all varieties of skimmer mixes etc.
I have not seen any microscopic dino grazers - or any evidence of them. I see live dinos and dead dinos, but no microlife eating dinos.
(I am aware that the presence of some bacteria can make dinos stop functioning, and I wouldn't be able to see that.)
I was really hoping to find an oxyrrhis or gyrodinium munching on some amphidinium. nothin.

That kind of predation can often go in either direction in dinoflagellate food webs... In all likelihood, the amphidiniums so outnumber the heterotrophic dinos and other potential predators/grazers that they're eating them faster than they're being eaten. And just because you don't have toxic dinos, that doesn't mean that your dinos aren't producing toxins -- maybe they're better targeted at the microfauna and hostile bacteria that are actual threats to the dinos, so we don't register them as "toxic dinos" in our heads because they're not killing animals we care about.

Skimmers collect and concentrate coral mucus and other detritus, so maybe they support a micro-ecosystem dominated by secondary producers that's biologically distinct from the dino holobiont. Like a wildlife refuge surrounded by farmland -- take it away, and the creatures that were living there don't have anywhere to go.

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Originally Posted by DNA

I introduced the Coccolithophores to the readers of this thread a couple of years ago, but nobody seemed to be interested.

I am. That's why I quoted your introduction and put some information about cocos in the megapost on page 101.

I recently stumbled across a hint that the heterotrophic species oxyrrhis marina prefer eating armored E. huxleyi cocos to naked E. hux. Weird, eh? Maybe naked cocos have more effective chemical defenses. Unfortunately, it's just a reference to a paper that doesn't seem to be online anywhere, so I don't know that it's true or why it might be so.