Corals W/ Attitude: Aggression & Toxicity

water_baby83

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Corals With Attitude
Understanding Classifications of Aggression & Toxicity

So, for anyone who's ever entertained the idea of owning corals, or for those who have in the past and/or currently house them, it’s no secret that there are general classifications appointed to different species, dependant on their natural behaviors and compatibility in mixed community tanks. These classifications are meant to make the potential owner aware of the level of risk they may pose in a tank, and sometimes, even to the owner. Problem is however, that for the most part, people don’t generally understand the differences, rather, they accept what they’re told, and try to combine corals which fare well together. While this is always encouraged, I feel any aquarist would benefit from a firm understanding in just why these corals get the ratings they are given, and what those ratings themselves, mean. Even still, there are those who ignore these “warnings”, and determine that if they simply place them far enough apart, or keep the tank in good standing, that it doesn’t matter which corals they house together. This misunderstanding comes mainly from the ABSENCE of understanding the characteristics which earn these animals the classifications they have.
A good thing to remember, is that just because corals aren’t the "snappy", "Fast moving" and "territorial" little beasties you'd expect to see in noted aggressive fish and inverts, don’t fool yourself into thinking that they are defenseless pretty little ocean flowers you can bouquet together without incident. Do that, and you could find yourself with chaos in your tank.

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So now we cover the most common classifications any hobbyist is sure to see when coral shopping. Those include;
  • Peaceful
  • Semi-Aggressive
  • Aggressive
  • Toxic
And the most common questions one might have regarding the above mentioned classifications. Questions such as;

  • What do those vague terms even mean?
  • When is it “ok” to mix corals of differing classifications?
  • What risks are posed to other members of the tank?
  • Are any corals actually dangerous, or can they be harmful to me?
  • What types of aggression can/do corals display?
  • How would I be able to recognize an aggressive coral, even if not labeled as such?
  • How would I work to avoid - or resolve coral aggression & conflict?
Those questions, and more, are what this sticky will hopefully prove to answer!

Let’s start with the classifications themselves. . . .

PEACEFUL – When a coral is labeled “Peaceful”, one can rest assured that this coral isn’t one to pose a risk of chemical warfare in your tank, generally lacks any stinging nematocysts, doesn't dispatch sweeper tentacles, and isn’t one of which might prey on, suffocate, or otherwise declare war against another member of your coral community. Additionally, these corals present no risk to the aquarist either. This isn’t to say however, that they withstand any of the above, as these corals, though many are hearty in their own right, lack the ability to adequately defend themselves from more aggressive species, and because of that, they aren’t ones you’d generally want to mix with more aggressive ones. Think of it this way – you wouldn’t expect a Piranha and a Blue-Gill to be buddies. However, other Piranhas together, could do just fine. Same goes for corals – if you’re going to mix them at all, you need to be cognizant of not only their defense mechanisms, but their offensive maneuvers too. Peaceful corals lack much of either, and tend to fare much greater when kept with other, less “combative” corals. A perfect example of common peaceful corals would be those within the Zoanthid class.

SEMI-AGGRESSIVE – "Semi-aggressive" corals, though not particularly hazardous in a community reef system, are ones which, if proper caution is not taken with placement, tank mates and adequate living space, there can be trouble. Though corals falling within this classification have been known to get into battles with other tank mates, they generally are not ones which will initiate the fight, so to speak, and typically will recoil when a more aggressive coral is the irritant. Semi-aggressive corals commonly posses sweeper tentacles and/or stinging nematocysts. In some semi-aggressive corals, the stinging nematocysts are present in the sweeper tentacles themselves, which are deployed as a sort of "patrol force" to sweep the coral's proximity. A good example of two corals commonly considered semi-aggressive would be the Frogspawn and Hammer corals. If another coral were to approach, and encroach upon the semi-aggressive coral's immediate space, and sweeper tentacles were to make contact, the tiny barbed nematocysts would fire involuntarily, potentially wounding the invasive animal. But corals aren't the only who could be affected by another's semi-aggressive nature. Fish coming into contact with sweeping tentacles can also feel the "sting", which is why it is important to place these particular corals in areas which accomodate their reach, affording co-habitants room to skirt around them. Though semi-aggressive corals can hold their own fairly well in a battle, and can be a bit territorial and defensive, they generally can coincide rather peacefully if kept at a distance from lesser equipped corals, and afforded ample room to "claim". These corals pose little threat to humans as our skin is generally too thick to feel, much less be afflicted by their defenses without repetitive and prolonged exposure, or hyper sensitivity / allergy.

AGGRESSIVE – Corals which fall under the category of "Aggressive", have in most cases, well over earned their right to be labeled as such. Corals within this classification are highly temperamental and can really pack a damaging punch to any who dare get in their way. Possessing not only sweeper tentacles and stinging nematocysts, these corals - with select species - can not only defend themselves heroically against assailants, but can also, and will, get up and bring on the fight to another who has come too close. Corals of the Cynarina genera are a perfect example of aggressive corals which have no issue in confronting anyone or anything which gets in it's way. (Have you ever been messing around in your tank and found your wrist or fingers being wrapped in the tentacles of an anemone? - They aren't shaking your hand, lol) Additionally so, many aggressive corals are also considered such, not for their blatant attacks, but rather, for their sense of superiority, and ability to out-grow, and effectively grow over other nearby corals. Further still, there are corals within this classification which posses the ability to induce chemical warfare inside your tank, severely damage tissues - mainly by burning (even of the aquarist in some cases!), dwarf the growth of and even kill nearby corals with a rather medial effort. Though not impossible to keep with other corals, these are ones which require a significantly greater knowledge base from the hobyist, and a considerably well thought-out environment, where they are provided with more than enough room to thrive, and are kept separate from less combative corals as best as possible. Do note however, that when taking known aggressive corals, and placing them into a mixed community tank, you're never Guaranteed a peaceful neighborhood, and daily monitoring of the tank is sometimes necessary to avoid unexpected disaster, and unless you have a rather large tank (Over 100gal), aggressive species are ill-advised for the vast majority.

TOXIC – There are corals still, which can be considered the "Terminators", viciously earning their place within the classification of "Toxic". Corals labeled as toxic are nothing short of a game of Russian roulette to the aquarist, as these corals not only posses the temperaments of aggressive species, but also, have superior weaponry, which allows them to declare war on, and damage, if not kill, all who are unfortunate enough to be within close proximity. These corals accomplish such assassinations by means of mesenterial filaments and terpenoid compounds. What the heck are those? - I'll tell you below in detail. These weapons not only knock out opponents like it's cool when in close quarters, but also provide long-range attacks as lethal chemicals are ejected into the main water column and as simularly as "tear gas" can clear a room and drop a crowd - so can these toxic compounds, which if not diluted rapidly and more delicate species removed, can cause massive destruction. Being in the wild is all about survival of the fittest, and evolutionary demands as direct results of competition.
[SIZE=-1]With all of these corals emitting all of these toxins, how can there be any corals left alive in the ocean? Simple: Dilution. The ocean is so big that the emitted toxins are spread over a very large area, diminishing their effectiveness. The corals' defense mechanisms and ability to heal, grow and reproduce are also essential for survival.
[SIZE=-1]Unfortunately, due to their size, most aquariums do not have the ability to dilute the toxins as well as the oceans. Whatever toxins that are emitted in an aquarium circulate in the water currents until they land and stick to something (i.e. another coral, a fish). The smaller the aquarium, the more concentrated the toxins will become. Because of this, to avoid a toxic-soup created by some rather pissy corals, be aware of which corals have the greatest potential for emitting toxins::




Ichthyotoxicity of Some Soft Corals

Group
Toxic Species
Nontoxic Species


Alcyoniida
58
20
Loboohytum ssp.*
9
1
Sarcpphyton spp.*
13
2
Cladiella ssp.
8
1
Sinularia ssp.*
28
15
Alcyonium ssp.
0
1
Nephtheidae



Lemnalia ssp.*
9
1
Nepththea ssp.
12
7
Dendronephthya ssp.
4
11
Capnella ssp.
0
9
Xeniidae


Xenia ssp.
6
1
Cespitularia ssp.*
3
4
Efflatounaria ssp.
4
6
Anthelia ssp.
1
1


[/SIZE]
Mechanisms of aggression

Corals have developed several specialized mechanisms for protection and competition with other corals. These include sweeper tentacles, mesenterial filaments, and terpenoid compounds (Ates, 1989). The picture at the left depicts incompatabilities between several coral species. Incompatabilities may be indicated by a color change, such as the white discoloration of part of the finger leather coral on the left. In reaction to nearby corals, the large tan mushroom coral in the middle has concentrated its poison in the white ends of its tentacles.


Coral Warfare
[/SIZE]Explanations of Types of Coral Aggression

Sweeper tentacles



Sweeper tentacles are the most common defense mechanisms in the hard corals. These mouthless elongated tentacles form the outermost portion of the coral colony. When a sweeper tentacle encounters a competing coral, it may attack the competing coral and literally "burn" the offending coral to the point of either killing it or severely damaging it. This "burning" is the result of specialized stinging cells called 'nematocysts' that are present in these tentacles (Talbott, 1984). The chemical present in these nematocysts is an alkali toxin similar to bee venom. A possible explanation as to why they are said to "sting one another." The relative toxicity of these tentacles differs among various species of corals, as does the length to which these tentacles can elongate (Sheppard, 1982). This degree of toxicity is important because:
  • If two corals fall into each other, the relative toxicity of their nematocysts will determine how long they can be in contact before serious injury results. It is possible for corals to be killed after falling into another coral after just fifteen minutes of contact.
  • When two corals have relatively equal toxicity in their nematocysts, it is possible for them to kill each other when they fall together. This is why it is important to take precautions to prevent corals from falling into one another.
The length of sweeper tentacles is not correlated to the length of the normal coral polyp and may, in fact, be many times longer. One of the most dramatic illustrations of this is in the sweeper tentacles present on Pavona cactus, a SPS (small polyp stony) coral that has branches which are only millimeters thick, and resemble potato chips. Despite the fact that the branches of this coral are only several millimeters thick, the sweeper tentacles that come out may be four or five centimeters long. Another example of dramatic elongation of sweeper tentacles is seen in the Crystal coral (Galaxea fascicularis). In this coral, normal polyps are only one to two centimeters long, while sweeper tentacles have been seen that are 30 cm long and contain a very potent nematocyst. Therefore, when selecting this coral, care should be taken to provide abnormally wide spacing between it and other corals.
Sweeper tentacles may appear when one coral is placed in close proximity to another or it senses the presence of another aggressive coral.

"I have observed this phenomenon first hand with my Crystal coral. When first placed in my tank, no sweeper tentacles appeared during the first three months. However, when I placed a Hammer coral (Euphyllia sp.) in this same tank, the sweeper tentacles appeared within three days. These tentacles also appear to be able to sense where the competitor is located in that, regardless of where I placed the Crystal coral relative to the Hammer coral, the sweeper tentacles always developed toward the Hammer coral. Interestingly, the Hammer coral also developed sweeper tentacles, but they were present all over the outer perimeter of the colony." - Michael Paletta

Mesenterial filaments
In addition to sweeper tentacles, several hard coral species can produce mesenterial filaments (also termed mesenteric filaments) from their stomachs. Corals of the genera Favia, Favites, Scolymia, Pavona, and Cynarina all have this capacity (Chadwich, 1987). These filaments can kill or devour other coral polyps through a process similar to digestion. Some corals even have the capacity to produce both sweeper tentacles and mesenterial filaments, enabling them to fight a battle on several fronts (Wallace, 1984).

Terpenoid compounds
The soft corals generally compete with the hard corals by releasing 'terpenoid' or 'sarcophine' compounds into the water to injure or impede the growth of neighboring corals, and then overgrow these impeded individuals in a process called "allelopathy" (Delbeek and Sprung, 1994). Like their name implies, these compounds are similar to turpentine in chemical structure and in most instances, are just as toxic. By releasing these compounds, the soft coral injures these neighboring stony corals and can thus grow above them, eventually blocking out the light that they are both dependent upon and thereby killing the underlying hard coral.



PREVENTING & CORRECTING A CORAL-WAR:
Understanding the Basics of Aggression Prevention & Necessary Intervention


Controlling aggression
While a miniature reef does not contain the great diversity of life that an actual reef does, provisions should still be made to try and minimize the aggression among corals. This can be accomplished by providing adequate spacing, reducing tip over potential, and taking action if aggression does occur.

**Provide adequate space
As noted previously, the relative aggressiveness among coral species varies. Consequently, when setting up a tank, adequate space, which is invertebrate free, should be given around each coral head.
Hard Corals: For LPS (large polyp stony) corals, this zone should be at least 15 cm in all directions, as sweeper tentacles have been reported to be at least this long (Sheppard, 1982). The distance between SPS corals does not need to be as great; a distance of 5-8 cm is usually sufficient. However, it should be noted that these are the fastest growing of all corals, so extra space should be allowed for this. For this reason, I suggest that a buffer zone of 30% of the coral colony's size be used when originally placing the corals in order to allow for growth. This may seem extreme and may initially make the tank look sparsely decorated. However, in a well-designed and maintained reef tank, this space will be almost completely filled within the first year simply from growth. If growth space is not provided, there will be a constant need to prune corals lest they burn and kill one another.






Soft Corals: For the most part, the space between soft corals does not need to be as great initially, since soft corals do not burn each other to the same degree as the hard corals do. Consideration in placing soft corals needs to take into account:
  • A faster growing coral will overshadow a slower growing coral and eventually starve it out for light.
  • These corals should be positioned so that their mucous and terpenoids do not come into direct contact with their neighbors. That is, these corals will do the least harm to other corals if the water movement in the tank is such that after the water moves across them it flows down an overflow and into a sump where the harmful compounds can be removed with either skimming or carbon filters.
Minimize tip over potential
Tip over potential is the likelihood that one coral will tip over and land on another coral, and as a result, burn or be burned by the other coral. This may seem trivial, but I have lost whole colonies of coral due to a small part of the colony being burnt as a result of it falling into another colony. The burned area became infected and consequently, the whole colony died. Tip over is particularly troublesome for SPS corals, which usually arrive unattached to anything. Therefore, when placing these corals on my live rock structure, I often use a dab of waterproof epoxy to hold them in place until they encrust over the area themselves. An alternative is to use rubber bands or plastic cable ties to anchor the colonies in a less permanent manner. If colonies do fall into one another they should be separated as quickly as possible, and any damage washed off in the current to try and rid the animal of nematocysts.

Reduce harmful effects of aggression
In a miniature reef aquarium, aggressiveness can have severe and dire consequences in that, if allowed to progress to its conclusion, a large and expensive coral head could die. If these sweeper tentacles or mesenteric filaments are observed, the reef keeper should make sure to move all invertebrates in their proximity out of the way. However, if these tentacles have reached their target, they should immediately be removed, allowing no touching with other organisms. If a portion of tentacle remains attached to another invertebrate, it should be physically removed immediately. If not, the toxin that the tentacle secretes will continue to work and will kill the colony to which it has become attached. Fortunately, if the reef tank is well maintained and no microalgae are allowed to grow on the skeleton, the coral colony may recover and grow back over the damaged area.




Information & Images From: Myself, Noted Texts, Marine Biotechnology Consultant Michael Paletta, Foster & Smith, colleagues, jstor.com, saltaquarium.about.com
 

David R

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Good info!

Only beef is the white and yellow font is unreadable for those of us using the MFKlight skin, any chance of changing it to a 'normal' colour?
 

J.Lake

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Feb 4, 2011
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wow a really great read! I knew lil about corals. Now I know a lil more!
 
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