Hello everyone, and welcome back to Tidal Gardens.
I, like many people who get into the reef keeping hobby, did so because of how peaceful
and serene coral reefs are.
The intense colors… the beautiful fish… tranquility… what’s not to love about
coral reefs right?
Well… this is a factory of lies!
Underneath that veneer of peace and tranquility is a world of aggression and endless warfare
between the corals on the reef.
Fish?
They are total jerks.
Peace and quiet?
Hell no.
If I’m scuba diving, I can tell you blindfolded if I am in a coral reef or not because it
is LOUD.
It sounds like a bowl of rice crispies IN YOUR SKULL.
Sorry about that, got a little carried away there.
This video though is all about coral aggression.
It plays a big role in how we place corals and build up our reef tank.
Let’s get into it.
Everything on a coral reef is trying to battle for more real estate and the organisms on
the reef developed specialized methods to wipe out their neighbors whether that be other
corals, algae, or inverts.
You might be thinking… but wait, not EVERYTHING is trying to kill each other… what about
symbiotic relationships?
That is true to an extent.
Years ago I did a video all about symbiotic relationships showcasing cooperation between
very unlikely partners.
One might get the idea that these sorts of things are common, but a coral reef is not
some beautiful utopia.
It is a landscape of intense competition for resources and these symbiotic relationships
only exist to further the competitive strategy of the partners.
For example, let’s look at the most iconic symbiotic relationship in the hobby, that
between a clownfish and an anemone.
In a vacuum, both the anemone and the clownfish would be better off alone.
The clownfish is getting constantly stung by the anemone, it has just developed some
degree of resistance.
The anemone is being constantly battered by the clownfish and often getting its tips bitten
off.
But… this relationship makes sense because the anemone provides protection to the clownfish
from potential predators and in return the clownfish provides protection to the anemone
from fish such as butterflies that might make a meal out of it.
So, there is a net positive from this relationship.
This shows that even in cases of cooperation it only makes sense in the context of competitive
advantage.
That was a little bit of a tangent but it illustrates the point that every coral or
invert we place in our tank has some mechanism of competition that they are more than willing
to unleash on its neighbors.
As responsible reef keepers we should take that into account when deciding on both acquisition
and placement.
And THAT is what this video is really about.
So let’s start talking a bit about what those mechanisms are.
First of all, corals possess nematocysts, or stinging cells.
Nematocysts are used for both prey capture as well as defense.
These venomous cells are not unique to corals as they are found in anemones and jellyfish
as well.
Some organisms developed adaptations to acquire nematocysts when they cannot produce the cells
themselves.
Zoanthid eating nudibranchs for example eat the polyps and store the nematocysts in these
sacks on their backs.
That is why often times the nudibranchs take on the coloration of the zoanthids they have
been feasting on.
How they work is each nematocyst is a pressurized capsule that features a coiled thread with
harpoon-like spines.
These cells are under a lot of pressure so when they are triggered, this coil fires out
and stabs into the target and injects its venom.
The power of the sting depends on the structure of the nematocyst as well as the toxicity
of the proteins it fires into the target.
Some stings are very mild while others are very intense.
For example, the nematocysts from a Pseudocorynactis mushroom are very sticky and it is able to
grab onto and hold large fish.
In fact, those can easily stick onto your hand and get lifted right out of the water.
Most of the time our skin is thick enough that coral stings aren’t that noticeable,
but sometimes people are more sensitive to a particular coral.
For example, some people are very sensitive to frogspawn and immediately break out after
handling a colony.
In extreme cases, people can get very ill.
Some people are allergic to the venom from carpet anemones and there have been reported
deaths from allergic reactions.
How this relates to coral placement is that some corals are able to create hyper weaponized
forms of tentacles called sweeper tentacles.
A sweeper tentacle is a greatly elongated tentacle with a concentrated mass of nematocysts
at the tip.
These sweeper tentacles are most commonly found in large polyp stony corals such as
euphyllia, certain brain corals, galaxea, the list goes on but they are also found in
some small polyp stony corals such as Pavona.
If you have a coral that is capable of sending out sweeper tentacles, it is important to
give it a lot of room in your tank because they can cause a lot of damage to neighboring
corals.
This is often easier said than done.
Some corals can extend sweeper tentacles up to a foot away.
Next up are two short range weapons, mucus coat and mesenteric filaments.
Mesenterial Filaments are the inside guts of a coral that some species can expel onto
nearby adversaries.
Mesenterial filaments contain nematocysts as well as digestive enzymes and can do significant
harm by coating the target for hours.
Eventually the coral retracts these filaments leaving behind a clearer substrate to grow
upon.
It is thought that mesenterial filaments used in this way are used both for aggressive expansion
as well as nutrition for the coral when they are withdrawn back into the coral.
Often times this behavior happens at night so it is entirely possible to have two corals
situated close to one another be fine but when you wake up the next day one of them
is completely dead... a victim of a mesenterial filament attack.
Almost every type of coral is capable of extending mesenterial filaments but some are more aggressive
than others in this regard.
I see them commonly in favia, favites, pectinia, hydnophora, and many types of chalice corals.
This next or is a bit of speculation on my part but it is an observation of mine for
years.
Mucus coats on various corals can cause serious damage to other corals even after brief contact.
The mechanism for this hostility isn’t well documented but it is pretty clear that whatever
it is it happens quickly.
It is not uncommon for a coral to fall off of the rock scape face down on another and
both corals immediately start showing signs of damage.
If left that way for a few hours both corals could die outright.
There are some studies that indicate the mucus coats of corals provide all kinds of benefits
such as UV protection, microscopic prey capture, and protection from detritus settling on the
coral by periodically shedding the coat away.
On the flip side however there are studies showing this mucus coat is also a dense breeding
ground for bacteria and viruses.
Like I said I am not sure what makes the mucus coat of a coral tick, but in practical terms,
it is important to place corals in such a way that you minimize the likelihood of contact.
Anticipate future growth and make sure to place corals securely so they don’t lean
into or worse yet fall on top of each other.
The last coral aggression adaptation I will discuss in this video is chemical warfare.
Some corals don’t necessarily pack a mean sting or barf up their guts and dissolve their
neighbor.
Corals such as these toadstool leathers can secrete toxic compounds into the water that
slowly poisons everything around it.
How this manifests is that other corals around it especially stony corals simply stop growing.
The secreted toxins are metabolites which may include:
Terpenoids which are a super diverse group of natural compounds that are often associated
with protective oils.
For example some plants have an oily coat that makes them toxic to insects and other
herbivores or termites have terpenoid-based oils that make them unappetizing to potential
predators.
These terpenoids are also precursors of polyhydroxylated steroids that have been detected as well from
certain leather corals.
There are also Acetates and Polyamine compounds that are all potentially bio active.
In fact, several of these compounds are being investigated for therapeutic uses because
some are inhibitors of chemical pathways which are very interesting in drug development circles.
To sum that all up, corals are capable of excreting a cocktail of bio active compounds
in an effort to wipe out neighboring organisms.
The corals associated most with these chemical toxins are leather corals like sarcophyton,
lobophytum, lemnalia, etc.
So what can we as home hobbyists do about corals that engage in chemical warfare?
Some aquarists chose to avoid these corals altogether especially those that are trying
to create an SPS dominated tank.
A tank full of acropora can be challenging enough without adding large corals that can
stunt their growth into the mix.
Having said that, there are plenty of people that keep stony corals with leathers.
It may not be ideal but it can be done.
There have been plenty of times that I have kept leather corals and acropora in the same
tank.
If you decide to try something like this in your reef aquarium, there are three techniques
that can help.
The first technique is to perform more water changes.
By changing out water, this will serve to dilute the concentration of toxins that build
up in the tank.
Second method is running activated carbon.
Activated carbon works by permanently binding up compounds through adsorption which happens
at the surface of the media.
As the media fills up it will have to be replaced, but activated carbon is inexpensive and readily
available.
The third and by far the least commonly used method is to run ozone in the tank.
Ozone is O3 a highly reactive molecule that has powerful oxidizing properties.
In an aquarium application it is generated by an ozone machine, usually by passing oxygen
through an electrical field splitting the O2 molecule and allowing the oxygen atoms
to re form as ozone.
In the aquarium, ozone has a variety of effects such as clearing up the water as the ozone
breaks down tannins that give our aquariums a yellow cast.
It also virtually eliminates any tank odors.
The effect we are interested in for this discussion is how affects the toxins that corals can
emit.
The extreme reactivity of ozone causes these toxins to break down upon contact to less
harmful compounds with little to no bioactivity.
There are severe downsides to ozone, such as safety risks if there is a malfunction.
If you are interested in trying ozone, as I am, be aware of the risks and have security
measures in place to detect possible leakage of ozone into the air.
All right.
That pretty much does it for our discussion on coral aggression.
To sum things up, corals developed all kinds of adaptations to gain a competitive advantage
in the battle for real estate on the reef.
In our home aquariums we have to be conscious of these in order to find the best location
for them long term.
I hope you enjoyed the video and please leave a like on the way out.
Best of luck in your own tank and I hope to see you all next time.
Happy reefing.