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Old 08/15/2015, 09:27 PM   #1537
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Originally Posted by 34cygni View Post

I read the entire thread. It's an epic. I totally feel DNA's pain.

Maybe I can help you guys make sense of what you're seeing...

The thing about mixotrophic dinos is that they're predators that acquired the ability to photosynthesize, not autotrophs that evolved into predators. That's why if you treat O. ovata like algae, you lose.

The big mystery is where are dinos getting their nutrients from? Especially in a ULN system?!? Even scientists seem perplexed...

The reason nobody can correlate nutrient levels with dino blooms is that the dinos aren't operating in autotrophic mode. Ostreopsis ovata can do that if there are enough nutrients in the water...

...but obviously that's not what's happening in our reef tanks. When O. ovata (or any dino) is nutrient-limited, it solves the problem the same way we do: by eating something. That's what's happening in our reef tanks.

Think about it. What do you guys know about dinos?

Remember the evolutionary history of the enemy: mixotrophic dinos are predators that acquired the ability to photosynthesize. These bacteria, the cyano... They're food. Dinos are no more symbiotic with them than people are symbiotic with cows. I mean, yes, we protect cows and we feed cows and we want cows to be fruitful and multiply, but that's because we eat cows. On paper, domestication is a big win for cattle -- there are lot more cows in the world than there would be if cows were free to gambol and frolic in a natural landscape filled with predators and diseases -- but the only benefit an individual cow derives from its relationship with humans is in the abstract philosophical sense that existence is better than nonexistence. We're the ones who benefit from that relationship, as dinos do from theirs.

Heterotrophic bacteria are rich in phosphorous; diazotrophic cyanobacteria can fix nitrogen and are rich in iron. That's the hat trick -- the big three limiting nutrients in aquatic ecosystems, right there.

This isn't my idea. It popped up in a scientific paper on red tides from 2010 and so obviously applied to O. ovata in a ULNS reef that my jaw dropped open when I read it.

Red tide dinos aren't benthic, of course, but O. lenticularis is...

In other words, not only are the dinos eating heterotrophic bacteria, they're farming their preferred food species of heterotrophic bacteria!

>The total bacterial cell/dinoflagellate cell ratio remained
>essentially constant through the initial 28 days of culture
>growth. Following this period, there was a steady,
>significant increase in the total bacterial cell/
>dinoflagellate cell ratio through 49 days of culture growth.

That means that the dinos were running the show for the first month or so, but then they lost control and the system shifted to a state in which bacteria were ecologically dominant. What happened?

>The percent total bacteria directly associated with the
>dinoflagellate cells was high (above 70%) in the inocula
>used to initiate the dinoflagellate cultures in this study.
>This percentage decreased significantly (to values below 10%)
>during the first 7 days, followed by sharp increases (60 to
>80%) at 21 to 35 days of culture growth. ...
>Peak dinoflagellate culture growth rates (first 4 to 7 days
>of culture, Fig. 1) were associated with reduced numbers of
>bacteria directly associated with the dinoflagellate cells
>while peak relative dinoflagellate cell toxicity was
>associated with a significantly increased fraction of closely
>associated bacteria.

The dinos start off with plenty of food (over 70% of the bacteria in the flask) and eat their way through it in the first week, reproducing rapidly while their food bacteria drop to 10% of the bacterial population. The dinos respond to this crisis by producing poison to suppress competing bacteria and encourage the growth of their food bacteria. They're like farmers spraying weed killer to prevent competition for nutrients in the soil and maximize the growth of their crops, and the population of the dinos' bacterial "symbionts" rapidly recovers over the next two weeks to over 60% of the total bacterial population, preventing a crash in the dino population.

Maximum measured toxicity comes at week 4, corresponding to a decline in the population of the dinos' associated bacteria to about 50% of the total population. The dinos have hit a point of diminishing returns. Metabolic waste products and the physical remains of dead dinos and bacteria are piling up in the mucilage -- all the stuff the dinos' bacteria can't eat -- and more and more poison is needed to keep unwanted bacteria away from that growing food resource, but now it looks like that strategy is failing and their food supply is threatened.

>Later stages of culture growth (35 to 49 days) were marked
>by reductions in dinoflagellate cell toxicity and relatively
>uncontrolled increases in the total bacterial cell/
>dinoflagellate cell ratio. ...declines in dinoflagellate
>culture density and toxicity corresponded to uncontrolled
>increases in the total bacterial cell/dinoflagellate cell
>ratio and decreasing proportions of bacteria directly
>associated with Ostreopsis cells.

At week 5, the dino population is declining. Interestingly, the population of dino-associated bacteria rebounds to over 80% of the total bacterial population -- in all likelihood by eating dead dinos. Even more interestingly, the dino population doesn't rebound along with their food supply, but instead continues to dwindle in weeks 6 and 7... Obviously, something has changed.

The shift from a system dominated by dinos to a system dominated by bacteria resulted from eutrophication. In a weird way, it looks like ostis are in the same boat as we are -- they're battling eutrophy, too -- and I suspect this explains why "the dirty method" of dino control works. Getting a little sloppy with the housekeeping just helps nature take its course, moving up the eutrophic tipping point where opportunistic bacteria and protists can invade the mucilage and overrun the ostis' bacteria farm.

And speaking of opportunistic bacteria...

Turning skimmate into probiotic tea?!?!?!? Pure genius. Thanks, Montireef!

But DNA provides us with counterexamples...

I'm so sorry, DNA. I thought you had a chance.

It looks to me like heterotrophic bacteria are the foundation on which ostis build. These bacteria are rich in phosphorous. Dinos are P-rich organisms, as well, but less so than the bacteria, so there's excess phosphorous in their diet. This waste phosphorous is used to recruit cyano, which is also P-rich, but less so than the dinos. And now the dinos have access to P from the bacteria and N and Fe from the cyano. Sky's the limit.

I thought Montireef outcompeted the ostis' bacteria by triggering a minicycle when he added LR. A cycling bacterial biofilter is basically a series of overlapping bacteria blooms, during which nutrient demand is very high. Montireef's experience suggests that slowing the reproduction of the food bacteria by giving them some competition can cause an established dino population to eat itself out of house and home in a matter of days. The addition of a massive dose of heterotrophic bacteria and protists -- Montireef's probiotic zoom juice -- to the system thus seems like the perfect follow-up: the dinos, stressed and perhaps turning on each other because of the sudden scarcity of food, couldn't fight off the invasion. A combination of starvation, hungry protists and microfauna, and "algal degradation by bacteria" apparently overwhelmed the dinos. In essence, Montireef artificially tipped his system into a state where it was dominated by heterotrophs... It's the dirty method without the dirt.

But DNA couldn't repeat the experiment. I wonder... Montireef reported snails pooping black for almost a week. Did your snails do that, too, DNA? I'm wondering if Montireef's skimmer was off when he dosed, and if you left yours on just that one time you checked the skimmate cup less than an hour after dosing, or if it was on every time...?

The example of O. lenticularis suggests that benthic dinos secrete poison at least in part to control the population of bacteria around them to favor their preferred food species. If O. ovata is doing the same thing, then parachuting in a zillion tiny globs of colloidal organic carbon infested with heterotrophic bacteria and protists seems like it would be absolutely the last thing it wants.

Ecology of a bloom of Ostreopsis cf. ovata in the northern Adriatic Sea in the summer of 2009

Cell Growth and Toxins' Content of Ostreopsis cf. Ovata in Presence and Absence of Associated Bacteria

Growth, Feeding and Ecological Roles of the Mixotrophic and Heterotrophic Dinoflagellates in Marine Planktonic Food Webs

Associated Bacterial Flora, Growth, and Toxicity of Cultured Benthic Dinoflagellates Ostreopsis lenticularis and Gambierdiscus toxicus
Mind blown![emoji33] [emoji100]

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