The more coral we have, the more likely we are to unwittingly introduce a disease.
Large scale coral facilities like our online coral stores are particularly at risk.
Probiotics can help with that though, we just need to figure out exactly which types are
best for our hobbyist corals.
You could be the person who figures it out!
What are probiotics anyway?
Well, coral has a lot of associated bacteria - what we think of as a coral is in fact a
large community of sorts, called a coral holobiont.
What we think of as a coral is really a mix of Coral, fungi, viruses, archaea, algae and
more.
Of all those, the thing you hear most about is Symbiodinacea, the dinoflagellates that
live amongst the coral’s tissues and provide nutrients they get via photosynthesis.
This nutrient source is the reason our coral needs such strong lights, without our reef
tank lighting the symbiotic dinoflagellates can't do their thing.
Little critters like bacteria and algae actually live throughout our corals.
There are a few distinct populations that most corals have - distinct groups are found
in the mucus layer, deeper in the coral's tissue, and still others live their lives
entirely within the coral’s skeleton.
Knowing what sorts of bacteria live where, and what they do, is sort of the cutting edge
of this science right now - and it’s key to being able to design a probiotic mixture
that will help corals survive climate change, or grow faster in our own reef tanks.
That’s not all that probiotics can do though.
Probiotics can help with absorbing nutrition, they can make corals more resilient against
stress, and some types can even mitigate disease.
We’ve seen in labs that various bacterial strains can help corals with increased bleaching
resistance, reducing the impact of diseases, enhancing energy reserves and even increasing
calcification rates.
Some of these effects might in fact be due to the coral eating the probiotic bacteria
when they’re added.
I’ve talked many times about the benefits of feeding your corals, and some people are
even using this idea to try to target slow-release probiotics to corals.
Not all bacteria are good though.
So, how can we test potential probiotic strains of bacteria to find the good ones?
Corals have very unique combinations of bacteria growing within them.
Luckily, these tend to be species specific rather than a unique fingerprint to an individual
colony.
This means that the first step is knowing what you’ve got.
An Acropora millepora may not respond to the same probiotics as an Acropora hyacinthus
because it is colonized and uses different bacteria in the wild.
For some well studied species, you can find this information in papers.
The easiest place to get bacteria from on a coral is it’s mucus.
You can swab it, or even hold the coral out of the water and collect the mucus as it drips.
There are distinct microhabitats in a coral though, so it’d be important to also sample
some of the tissue and skeleton and not focus solely on mucus.
Getting the general bacteria from the coral is only the first step though.
From here, you need to grow the bacteria.
You can use special agar plates that feed certain kinds of bacteria to select some probiotic
candidates - this is an active field of research and there are lots of options popping up for
working with coral holobionts in this way.
For instance, there are plates that target bacteria which can fix nitrogen from the environment,
or bacteria that stimulate immune responses, and these can be used to select for traits
that you want to find in a potential probiotic strain.
Once you’ve grown some bacteria you’d be well advised to screen it for known pathogens
before using it on your coral.
There are databases available where you can screen genomes to identify some of the more
common problematic bacteria.
You may also find that one of the bacteria you’re growing produces antibiotics - great
for the coral - not so great for the other probiotic strains you might want to use alongside
it.
The next step is actually getting your bacteria to your coral.
If you’re targeting the coral’s mucus, you might be able to simply broadcast your
cultures into the tank’s water.
That’s easy, and if it works that’d be ideal.
This works well in aquaculture and in reef tanks, but it’s harder to do in the wild
on a coral reef, so there is a lot of research going on into the best way to get a probiotic
mixture to coral.
Another option is to enrich the coral’s food with bacteria.
You can gut-load rotifers, and several of our corals will gladly eat live rotifers.
Not all though.
An artificial shelf-stable food that can be enriched with probiotics would be ideal, but
such a thing doesn’t exist yet.
Maybe you could help find that for us?
It’s much harder to get probiotic strains into the deep tissues or skeleton of a coral.
It might be possible to do this in an aquaculture farm or frag tank though, as very small corals
might be likely to take up some of these sorts of bacteria as they grow.
More research is needed, including getting to the stage of reproducing coral in the hobby
beyond simply by cutting frags.
I hope this was interesting, and maybe got some wheels spinning for you.
If you’ve got the space, are reasonably inclined in microbiology or know someone who
is, this might be an interesting avenue of research that you could explore with the reef
hobby.
There’s a bunch of papers being published every month on coral probiotics or coral holobionts
- one paper that I’ll link down below is titled “Probiotics for coral aquaculture:
challenges and considerations”.
It was published in Current Opinion in Biotechnology.
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Thanks for watching!
Be kind to each other, stay safe, and have a fantastic day!
Bye!