The interaction of anemones and clownfish is a charismatic example of a mutualistic
partnership in which the anemone protects the clownfish against predators, while the
clownfish provides the anemone’s endosymbiotic zooxanthellae algae with excreted nutrients
like ammonia, sulfur, and phosphorus.
Hi guys and girls, I’m ReefMan, and this time we’re talking about new research on
how clownfish avoid being stung by their host anemones.
There was recently a paper published about this, titled “Microbiomes of clownfish and
their symbiotic host anemone converge before their first physical contact”.
There’s a link down below if you want to check out all the details.
The paper is open access so I’d encourage you to check it out if you’re interested.
There are a few theories out about exactly how clownfish avoid becoming a meal for their
anemones.
Maybe clownfish benefit from some built in protective mechanism in their skin mucus.
Maybe the mucus is just sort of a natural chemical camouflage against the stinging nematocysts
of the anemone like a snake’s pattern might help it blend in amongst leaves on the forest
floor.
Another theory is that clownfish might nestle up against the tentacles of the anemone in
order to spread some of the anemone’s mucus on its own body - again like a chemical camouflage
- only this time maybe the clownfish aren’t born with it.
Really, both theories could be correct, there’s no reason why both couldn’t be taking place.
More research is needed!
Clownfish are known to hover in the water near their new found hosts before making physical
contact.
What’s the reason behind this?
Are they maybe waiting for some change in their skin’s mucus before diving into the
stinging tentacles?
There are some research papers out there on this, but none that go to the lengths this
paper did in testing the effect of being in the same water vs being able to touch the
anemone vs having no anemones in the water at all.
The authors of the paper wanted to test two hypotheses.
First, is the relationship between clownfish and their anemones associated with a large
change in their skin microbiomes during acclimation?
And second, if so, does this skin microbiome restructuring take place even before any physical
contact happens?
The team took 18 Heteractis magnifica anemones along with 18 captive bred Percula Clownfish
for their study.
They immediately swabbed about 50 percent of the clownfish’s skin with a cotton swab
to find out what sort of bacteria lived there.
They did the same with the anemones, swabbing tentacles after lowering the water level in
the tank to expose some of them.
They also sampled the water in the tanks itself, so that they could find out if there was some
change in the planktonic bacteria that might be influencing things.
They set up several aquariums and plumbed them so that some of the clownfish were in
water that never saw anemones - the control fish.
Some fish were in tanks that had no anemones, but in water that flowed through tanks with
anemones, and still other fish were housed in tanks that also housed anemones allowing
the two physical access to each other.
The team took several cotton swab samples over the study - at the initial start of the
experiment, after 15 minutes of interaction between clownfish and anemones, after 1 and
2 weeks of interaction, and then 1 and 2 weeks after they separated the fish and the anemones.
They ran extensive DNA tests on the samples to figure out what sort of bacteria were in
the mucus, and how much of it was present.
The bacteria present in the water from the tanks never changed in a way that made it
seem like a driving factor.
There was no impact on the bacteria floating around in the water by the presence of fish,
anemones, or even just with the passage of time.
On the other hand, after just 15 minutes of exposure the bacteria in the skin mucus of
clownfish with direct contact to their anemones had changed significantly compared to the
control fish.
Even the clownfish who were simply in the same water, but in different aquariums, had
changed.
For the fish that had direct access to the anemones, their mucus continued to change
even after they were removed back to tanks that had no exposure to anemones.
A similar pattern of changes happened in anemones except that they didn’t continue to change
when the clownfish were removed - the anemone mucus microbiome seemed to plateau and become
stable in its altered state before returning to normal within a couple weeks when clownfish
were removed.
One group of bacteria in particular seemed to be driving most of these changes - the
Cellulophaga species.
The DNA present was matched to Cellulophaga tyrosinoxydans - and this bacteria increased
in numbers in both the clownfish and the anemones.
It seems to take a week or so for this bacterial change to stabilize, but once it did it stuck
around in the fish.
There seems to be some sort of chemical signalling happening within the populations of Cellulophaga
living in the mucus of both fish and anemones.
When these animals are in close enough contact but not in direct contact, these chemical
signals trigger a huge population growth of bacteria - aligning the mucus of the anemones
with that of the fish.
Once this happens, the stinging cells in the anemone no longer react to the presence of
the fish.
It’s interesting that this can happen even without any physical contact.
From the study, it’s clear that Percula clownfish need only to be near their anemones
- they don’t need actual physical contact, although close contact like that probably
does speed the process along.
Without physical contact the fish and anemones still align, but not quite as well, and without
such a long lasting change as would have occurred with physical contact.
Given that the protective changes appear to be bacterial, and that both the fish and the
anemones change, it’s no wonder that wild clownfish usually host only a specific species
of anemone.
In reef tanks, they might host all sorts of things - but in the wild usually it’s a
very specific anemone.
That makes sense, now that we know there needs to be bacteria present that can signal through
the ocean’s water to each other in order for this process to work.
More research is needed for sure.
Is the protection purely a function of bacterial density?
What would happen if you used antibacterials on a fish, then reintroduced it to the anemone?
As with most science, the more we know, the more questions we have!
I hope you enjoyed the video.
Check out the links below if you want to read the paper for yourself.
Subscribe if you want to see more videos like this, stay safe, be kind to each other, and
have a fantastic day!
Bye!