Coral reefs are on the brink of collapse, and carbohydrates might be part of the answer
in how some corals make it through oceanic heat waves.
Water temperature rises as little as half to 2 degrees celsius is enough to cause mass
coral bleaching and causes a whole host of other problems for the coral.
It stands to reason that, in our tanks too, where stability is often the key to a thriving
reef, a heat wave or broken chiller can sometimes spell doom.
Mitochondria are the primary source of energy in most eukaryotic cells - cells like you’d
find in yourself, in your dog, and in corals.
Corals are special though, they host symbiotic dinoflagellates in the genus Symbiodinium
which themselves contain chloroplasts and can photosynthesize.
The combination of mitochondria and those symbionts give coral a lot of adaptability
- in the sunlight they can get food directly from the sun, and at night or when food is
plentiful in the water they can get additional food via their mitochondria, which convert
chemicals from digested food into something called ATP.
ATP, or Adenosine Triphosphate, is the basic molecule of energy for basically all living
cells.
It’s involved in a number of cellular processes, and as its phosphate bonds are broken energy
is released.
Both the photosynthesis of the Symbiodinium and the production of ATP by the mitochondria
are affected negatively by high temperatures.
Worse, because corals usually grow in bright tropical parts of the world, all that energy
coming in from the sun ends up creating things called Reactive Oxygen Species - chemicals
that can cause oxidative damage to the cells.
All those things you eat with antioxidants?
They’re to combat reactive oxygen species.
Reactive oxygen species are a problem for corals, and it’s not because they cause
fine lines and wrinkles.
In corals, free radicals impair carbon fixation, cause issues with protein folding, and cause
problems with the creation of ATP.
That’s to say, they’re bad for corals.
If we can avoid them in our corals, we should.
So, with all that going on when heat waves happen, how do corals survive at all?
How do frags make it through shows where the water temperature is likely less than stable?
What about during shipping?
Well, just like you and me, when corals are unable to get energy from the sun due to bleaching,
they turn to their energy reserves and their ability to eat fine particles of food from
the water.
This is one reason it’s so important to feed our corals regularly - without this additional
energy source you’re just increasing the risk of losing your corals if something goes
wrong.
Corals can store energy in proteins, lipids - that’s things like wax, fat, and oils
- and as carbohydrates.
Many species use lipids as the primary store, because they tend to last a lot longer vs
carbohydrates and proteins.
Coral can only get carbohydrates by eating or breaking down its own tissues.
Proteins ebb and flow with the season, and lipids are created by the coral itself - but
carbs, those must be eaten.
If it sounds like this is all a complex balancing act of building up energy before it’s needed,
you’d be right.
Environmental stress, like a heat wave, throws this balance into disarray.
When a coral is exposed to warmer than normal water, it’s basic energy expenditures - called
it’s basal metabolism - go up.
It takes more energy just to exist.
The coral spends energy on combating that oxidative stress from the reactive oxygen
species.
Corals contain genes that can be turned on to do just this, but it all takes raw materials
and energy that could otherwise be used for something else.
At the same time, heat decreases the coral’s ability to absorb nutrients, and it even damages
the ability to produce ATP.
Push the temperature even higher, and corals can begin partial anaerobic respiration in
addition to their normal aerobic respiration, which leads to significantly depleted energy
reserves and leaves the animal in an unsustainable downward spiral.
If the water doesn’t cool off quickly while maintaining otherwise perfect parameters,
this coral will not survive.
Once the energy is depleted and oxidative damage is no longer controllable, it’s over
for the coral.
Even if the coral can recover, it’s ATP remains depleted for months.
One study looking at the effect of temperature on energy and ATP in corals found that at
7 degrees celsius over normal, or around 91 degrees fahrenheit, the carbohydrate levels
dropped in Stylophora frags by 76%.
That’s a huge loss in energy reserves!
In the same study, lipid and protein levels did not change in the same way.
In this study, half the corals in that +7 degree group died.
As corals bleach they not only lose their symbionts.
They also lose some of their ability to absorb nutrients from the food they are able to eat.
This really highlights the importance of feeding our corals.
You never know when a heater might break, or when a power outage could happen, leading
to a stressful time in your tank.
You might be able to keep the tank livable for your corals, if only slightly, with battery
powered pumps and such, but still the tank will not be ideal.
In order to set our corals up to survive this period, we need to ensure they have substantial
energy reserves.
We feed our corals, or more accurately their symbionts, with our intense reef tank lighting.
But that’s only half of the picture, all corals also get energy via food - zooplankton
in the water.
We should ensure that our home corals are not robbed of this secondary food source,
as it’s increasingly being shown to be more and more important to the overall health and
long term survival of our coral.
If you’d like to learn more about this, I encourage you to check out a paper titled
“The reef building coral Stylophora pistillata uses stored carbohydrates to maintain ATP
levels under thermal stress.”
There’s a link down below in the description, and I think you can also find the PDF from
the author on ResearchGate.
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Till next time, be kind to each other, stay safe, and have a fantastic day!
Bye!