- What do you know about ammonium?
No, I'm not talking about ammonia,
I'm talking about the mostly non-toxic version of it,
ammonium, NH4; the toxic version is ammonia, NH3.
Either way, they should be undetectable
on a reef tank, right?
What if I told you that your corals might grow better
with just a little bit of ammonium in your water?
Am I lying?
Well, it's true, at least for Stylophora species,
but the science probably holds for Acropora
and other stony corals as well.
It's really a tiny bit that we're talking about here,
parts per billion.
And I bet that your feeding regime
is already providing this level as uneaten food
and fish poop breaks down in your tank.
Hi guys and girls, I'm ReefMan,
and this time we're talking about a neat paper titled
"Coral Productivity is Co-Limited
by Bicarbonate and Ammonium Availability",
and it was published in Microorganisms in April of 2020.
The article is open access,
so if you're interested, it's down below.
There's a link in the description, check it out,
and you can find it there.
In the paper, they're looking at the calcification rate
of Stylophora pistillata,
and the symbiotic dinoflagellates that live in its tissue.
And they're not just looking
at those dinoflagellates in general,
but looking at their rate of photosynthesis
and the quantity of dinoflagellates
that live in the coral's tissue.
As a refresher, many corals get a lot
of their energy from the sunlight, like a plant,
but they're not plants, they don't have chloroplasts.
What they do have instead is these tiny organisms,
dinoflagellates, that are just all throughout their tissue
and they come from the Symbiodinium genus.
And they do have chloroplasts, but again,
even those, they're not really plants,
but also they're not quite animals.
Dinoflagellates are strange creatures, right?
So almost all of our corals have millions, billions, really,
of these dinoflagellates cells throughout their tissue,
and those dinoflagellates provide some of the energy
that they get via photosynthesis back to their host coral.
In the paper, the team is mostly looking
at the photosynthesis
of those single-celled symbiotic organisms,
but they're also concerned with the overall number of them
that are found in the coral.
Would maybe elevating ammonium
and providing a carbon source increase the population
of those dinoflagellates?
Well, to find out, the team cut 264 frags
from six Stylophora pistillata colonies.
They fed them twice a day with freshly hatched Artemia,
Stylophora are one of the genuses known
to eat that live food.
Check out the video above if you wanna know more.
They suspended all these frags
on just nylon line in eight different aquariums.
They maintained the frags, let them grow, acclimate,
get used to it for five weeks,
and then they halted all of the feeding for two weeks
preceding the experiment.
In that way, the brine shrimp couldn't provide a source
of nitrogen or ammonium on their own.
Then they ran the experiment for 21 days.
The team tested four different variations.
You have to have a control
so the control just had ambient ammonium
and bicarbonate levels
that was found in their source seawater.
They also had a group in which they only increased ammonium,
one where they only increased bicarbonate,
and finally, they had a group where both ammonium
and bicarbonate levels.
Now, we're not talking about a big amount of ammonium here,
I mentioned parts per billion.
They increased it only that tiny amount
and total ammonium was only around 72 parts per billion
in the elevated ammonium tanks.
This is an increase of about four times
over the control concentration, give or take a little.
Your test kits at home,
they can't even detect that amount of ammonium
as it's less than 1/10 of one part per million,
and normally, one part per million is the lowest amount
that your kit is going to be able to detect.
For bicarbonate,
they used about 366 parts per million bicarbonate
which is about three times the control concentration.
So, what did they find?
Well, Symbiodinium concentrations
in the coral tissue increased within a week
with only ammonium supplementation.
The dinoflagellates also had more chlorophyll
and carotenoids in their cells as well.
This shows that the Symbiodinium were doing better
with the elevated ammonium.
They should be able to do more photosynthesis
and get more of that energy back to the coral,
and there were just more of them in the tissue.
The coral did better.
It grew about 23% more than the control frags group
in the same time period, measuring just calcification.
The tanks with bicarbonate also improved the overall growth
of the Symbiodinium.
Again, there was a higher density
in the coral's tissue by day seven,
and the dinoflagellates were just doing more photosynthesis.
The corals in this group grew 34% more
than the control frags did on average.
The largest result was in the final group,
where both ammonium and bicarbonate were increased.
Symbiodinium density in the coral's tissue was 40% higher
than the control group by day 7,
and 85% higher than in the control corals by day 21.
The total number of chlorophylls
and carotenoid content was also significantly higher,
leading to the corals in this group
having a much higher rate of photosynthesis.
In fact, it was 1.7 times higher than the control group.
The coral's overall growth rate was comparable
to the other groups where they elevated one or the other,
so even though the dinoflagellates were doing great,
the overall coral wasn't calcifying faster
than the groups only had more ammonium
or only more bicarbonate.
This study suggests that coral,
or rather it's dinoflagellate algae
that's living in its tissue,
is co-limited by both the availability of inorganic carbon
and nitrogen if you wanna optimize for photosynthesis.
The overall rate of photosynthesis seems to be limited
mostly by nitrogen availability,
while the growth and therefore the density
of the symbionts is limited by carbon.
In this study, increasing ammonium
provides an increased nitrogen source,
while bicarbonate gives a carbon source, of course.
Now, before you go out and dose your tanks
to 72 parts per billion ammonium,
it's important to note that really,
simply making the dinoflagellates happier
and denser doesn't always directly translate
to a benefit for the coral that houses them.
At very high density levels,
those organisms can actually turn to parasites,
parasite that keep nutrients for their own needs
rather than feeding it back into the coral's tissue.
This is really common when the coral itself is under stress
or when there's a high level of nutrients in the water.
In those cases, it's not uncommon
for the coral to eject all of its dinoflagellates,
that's called bleaching,
and it seems like the dinoflagellates can kinda sense this.
In order to better prepare themselves for open water life,
'cause they can live outside the coral,
they hoard chemicals just like you might horde things
if you knew you were about to lose your job
or go through some hardship.
I thought this was a pretty neat paper.
I've never heard of ammonia, or even ammonium,
having a beneficial effect on life.
I've always thought, just like you,
that coral reefs are better off
with the lowest possible amount of those compounds
in their water.
It turns out that life isn't that simple,
and even these harmful substances,
think of ammonia cleaners,
they can be useful in very small amounts.
Thanks for watching!
There's a link down below to the paper,
so check it out if you want to.
Don't forget to subscribe if you've made it this far.
Stay safe, have a great day!
I'll see you next time. Bye!