Too many people envision the reefs of the world to be some aquatic equivalent of "Bambi crossing a meadow" with some sort of miraculous "balance" amongst the life that occurs there. This is a dangerous precept for aquarists, as these areas are veritable battle zones with the life competing for space, food, mates... at a "tooth and claw" level. Most all benthic life we keep continues with this behavior in captivity. Overgrowing, shading, poisoning, stinging, eating its neighbors... Sometimes at great distances. Herein will be my statements re approaches to alleviate the major thrusts of this issue with stinging-celled life... All out competition is an omnipresent situation in captive reefs. Proper set-up... Starting with smaller specimens, rinsing them, quarantine, placing the less noxious to more in order, careful maintenance... and observation are all useful tools here.
Looking at most television and other media presentations re the worlds reefs, one gets the notion that these are places of pastoral perfection With static stands of dominant inplaced/attached life and shoals of colorful fishes passing by. This is a far cry from the truth, as most reef aquarists can attest. In fact, just thinking about what one sees on tropical shallows should cause a thinking person to wonder Just why is there so much polypoid life here? Does it make sense that predators wouldnt consume such ready fare? Looking a bit closer, one can clearly make out demilitarized zones between various specimens and with a bit more cursory examination, that there are definite patterns in the abundance, distribution and proximity of one organism type and its relation to others.
These facts are of use, importance to home hobbyists, as obviously all Cnidarian life has mechanisms for extending itself in space and time to the detriment of others near it. Various tools are used as we will see to outcompete neighbours for space, light and food and to prevent them in turn from outright being killed.
Various Competitive Means:
There are a few ways to classify the mechanisms used by Cnidarians to attain and retain their piece of paradise on reefs. Here is mine.
n Growth Means
n Physical Means
More Distal & Specialized: Acrorhagi
Most Distal: Sweeper Tentacles
n Chemical Allelopathy
Toxins produced that are deleterious to cnidarians, other
invertebrates, often fishes and even algae.
Competitive Means Details:
Growth Means: Overshadowing/Shading:
This is a principal strategy of the more fast-growing, reef-building families of stony corals, the Acroporids, Pocilloporids and some Poritids. Simply growing faster, taller, overhanging and crowding out other life forms below and aside their colonies to deprive them of light and settling foods.
Growth Means: Overgrowing:
Faster growing, more dominant by way of being more noxious or better stinging species can overcome and even possibly derive nutrition from slower growing, less noxious, less stinging ones that lose to them. This phenomenon is especially common among stoloniferans (polyps to hobbyists) and gorgonians (sea fans).
Though the contestants may not be chemically challenging to each other, simple proximal exclusion can deprive other life of light, current, foods, waste-dilution
Physical Means: Digestive Dominance:
Some Cnidarian groups can use their tentacles and extend other feeding structures through their body wall (mesenterial filaments) whose cnidocytes contain digestive elements. Some stinging-celled organisms can egest (throw up) buccal pellets, digesting near competitors.
Stinging Means: Proximal:
Nematocysts/Cnidocysts are cellularly derived structures that are
everted (turned inside out) given chemical (smell) and physical
(pressure) clues with either barbed ends of various sorts or
agglutinant (sticky) processes. These can be shot out with extreme
speed and pressure penetrating even a thickened skin Some are VERY
sticky, others are EXTREMELY toxic. And theyre the gift that keeps on
giving; can continue to sting, agglutinate off-animal, at much later
times as part of released mucus that can sting, poison other life.
Theyre especially prevalent in hard and soft corals and
Distal Stinging Mechanisms: Acrorhagi:
structural defense is widespread amongst coldwater Anemones, and found
in some hard and soft coral groups. The actual stinging structures are
called holotrichs, mastigophores.
More Distal Stinging Mechanisms: Sweeper
is the most common occurrence and source of trouble with stony coral
keepers but sweeper tentacles also occur in soft corals, other Classes.
Their mode of action appears as burning of adjoining species,
different genotypes of the same species. Occur in response and in the
direction of strangers. And sweepers can break off keep stinging,
The size of species, polyps is no indication of
the length of sweepers, nor most importantly, the number of cnidocysts
For example, even one inch Oculinds (Galaxeas) have sweepers of up to
12 length. Caryophylliids/Euphylliids very common as well. hierarchy of
stinginess can be arranged with species of the genera Fungia, Galaxea,
Goniopora being high, Lobophyllia being intermediate and Montiporas
Allelopathy: Poisoning Others:
Mostly gorgonians and soft corals, but about half of cnidarians produce allelopathic compounds in some quantity; some of their effects are profound, especially in aquariums vs. wild settings, where concentrations can be orders of magnitude higher due to a lack of dilution. Can be lethal to other livestock, including fishes and algae; however, the effects, degrees of toxicity are species to species specific and variable.
Allelopathogens are used for more than
offense/defense. They also serve to shed/avoid space and metabolic
parasites. Chemically, theyre mainly 'terpenoid' and
'sarcophine' <a class of Terpenes> compounds, but there
are many others. Higher reduction-oxidation potential (e.g. the
use of Ozone) is useful in destruction of these materials.
Some of the greatest volume producers:
Matters: What Aquarists Can and Should Do (or at least be aware
Signs/Symptoms of Overt Aggression/Poisoning
Treatment for Effects
Recognize the Signs/Symptoms of Overt
For stinging-celled life:
Rapid or slowed breathing and movement
Bleached appearance, especially in direction of
cnidarians. Slimy dissolution.
Means of Prevention: Selection, Acclimation
best methods of treating these issues of negative interaction is
obviously to avoid them altogether. Though not entirely possible, nor
even practical, the following are valuable to prevent extreme
Selection: Look for the best in
apparently healthy specimens; these are less likely to over-react in
the presence of established Cnidarian life in your syste
Acclimation of New Specimens: Is
best done in a plastic tray best, rinsing specimen/s individually, with
clean, system water, and discarding mixed water.
Quarantining: For a week or two allows you time to examine for new specimens for health, possible undesirable hitchhikers, and allows them to rest, shed slime, stinging cells, wastes...
Space: For dilution and spacing specimens, providing varied habitats: The bigger the system/volume the better. The larger the system, the more stable and the more hodge-podge and even crowded an assortment can be. Wastes are diluted and specimens can be more widely spaced initially, giving them more time/space to grow, time to undergo classical habituation (to ignore each other).
Careful stocking plan: Species selection,
placement, order: STUDY! Only through careful studying, reading,
conferring with other reefers assemble a working assortment.
Buy/Procure captive-produced stocks they do get along better. Provide
adequate initial, stinging, expansion and growth space between
specimens. Go slowly often cnidarians get used to each other over time.
Keep your system in dynamic equilibrium through regular monitoring and
Securing, sequestering of individuals,
colonies: Falling of specimens into each other or not must be
avoided by strapping, gluing, wedging, isolating in place ON/IN a
stable setting. Place rock, other structure on bottom of tank; larger,
flatter pieces first. Drill, tie, anchor structure together if
Adequate feeding, lighting/regimens,
All cnidarians need to be fed even principally
photosynthetic species/groups. Nutrition can be provided purposely or
indirectly via refugium culture, ancillary feeding of other stocks, or
For most set-ups, mixes of livestock, lighting
should be consistent. Light systems should be on timers, cycled on/off
Circulation should be vigorous and non-laminar. On
the plus side of poor water movement is the lack of chemical
communication and distribution of chemical and physical materials. On
the plus side of high water movement are export of same, distribution
of foods, oxygen, elimination of wastes, carbon dioxide, provision of
steady pH, RedOx, Biominerals
Biological, Physical and Chemical filtration,
augmentation, efficient skimming
The more complex the make-up of the system,
incorporating live elements, ozone/high/er ReDox, mud, reasonable
levels of biominerals and alkalinity on a steady basis the better. This
is accomplished with the use of refugium/s, macroalgae culture, DSBs, a
regular routine of established
Not Cnidarians Alone: Other Phyla: A Bit More
Fuel on the Fire
Cnidarians arent (by far) the only organisms with competitive mechanisms on/in reefs All animal, algal, plant and micro-organism groups have varied means of avoiding predation, securing space, other resources Some are much more potent than stinging-celled animals e.g. Sponges, BGA About the best one can do is again set up a good-sized system properly, stock it appropriately, maintain it adequately and remember the oxymoron dynamic equilibrium in keeping it so.
n At times Extreme Competition in the wild is mirrored in various fashions and degrees in captive systems.
n Much overt aggression and poisoning amongst cnidarians and their tankmates can be prevented, ameliorated by:
n Evidence of
Negative Interaction, Suggested Reactions
Ates, R. 1989. "Aggressive behavior in
corals". Freshwater and Marine Aquarium 12(8):104-105, 107, 110,
Calfo, Anthony. 2007. Book of Coral Propagation, 2d ed. Reading Trees, Pittsburg PA.
Delbeek, Charles. 2005. Reef Aquariums: Coral
Dubinsky, Z. [Ed.] 1990. Coral reefs. Ecosystems of the world. V. 25. Elsevier Sci. Publ., Amsterdam. 550 p.
Hauter, Stan & Debbie, undated. Coral Competition;Turf Wars in Coral Reef Tanks. About.com. Saltwater Aquariums http://saltaquarium.about.com/library/blank/bl_CoralCompetition.htm
Hidaka, Michio. 1985. Nematocyst Discharge, Histoincompatibility, and the Formation of Sweeper Tentacles in the Coral Galaxea fascicularis. Biological Bulletin, Vol. 168, No. 3 (Jun., 1985), pp. 350-358
J. B. C. Jackson and Leo Buss. 1975. Allelopathy and Spatial Competition among Coral Reef Invertebrates. PNAS | December 1, 1975 | vol. 72 | no. 12 | 5160-5163
O. Langmeada and C. Sheppard. 2004. Coral reef
community dynamics and disturbance: a simulation model. Ecological
Volume 175, Issue 3, 15 July 2004, Pages 271-290
Sammarco, P.W., J.C. Coll, S. La Barre and B. Willis. 1983. "Competitive strategies of soft corals (Coelenterata: Octocorallia): allelopathic effects on selected scleractinian corals." Coral Reefs 2:173-178.
Sebens, Kenneth P. & Julia S. Miles. 1988. Sweeper Tentacles in a Gorgonian Octocoral: Morphological Modifications for Interference Competition. Biological Bulletin, Vol. 175, No. 3 (Dec., 1988), pp. 378-387
Shimek, Ron. 2007. Coral crowding and combat. AFI 12/07.